BER Research Highlights

Search Date: October 19, 2017

200 Records match the search term(s):


November 01, 2017

Rapid Characterization of Northern Cold-Region Soil Organic Matter

Infrared spectroscopy discriminated variations in soil properties and extent of organic matter decomposition for Alaskan soils.

The Science  
Multivariate analysis of mid infrared spectra of soils collected from a 2800-km latitudinal transect across Alaska identified spectral bands that can be used to quickly discriminate variations in soil properties, estimate the quantity and chemical composition of soil organic matter, and assess the degradation state of organic matter stored in northern cold-region soils.

The Impact
Soil analysis using traditional laboratory methods are often time consuming and expensive, and require relatively large samples — limiting the availability of information on the spatial variability of soil organic matter composition and other soil properties. Mid infrared spectroscopy of small soil samples proved to be a promising technique for quickly and reliably estimating carbon content and differentiating the degradation state of organic matter stored in northern cold-region soils.

Summary
The amount and vulnerability of soil carbon stocks in northern cold-region soils are major sources of uncertainty in the representation of terrestrial biogeochemical cycles in Earth system models. Researchers led by Argonne National Laboratory investigated the suitability of diffuse reflectance Fourier transform mid infrared (DRIFT) spectroscopy — a non-destructive, cost-effective infrared light analysis method — to discriminate variations in soil physical and chemical properties needed to improve estimates of the spatial variability of carbon stocks and the extent of organic matter decomposition in these soils. Archived soils collected from a 2800-km latitudinal transect across Alaska were analyzed to provide a representative range of climate, vegetation, surficial geology, and soil types for the region. The chemical composition of organic matter, as well as site and soil properties, exerted strong multivariate influences on the DRIFT spectra. Spectral differences indicated that soils with less decomposed organic matter contained greater abundance of relatively fresh materials, such as carbohydrates and aliphatics; whereas clays and silicates were incorporated into more degraded soils. A single spectral band was identified that might be used to quickly estimate soil organic carbon and total nitrogen concentrations. Overall, the study demonstrated that DRIFT spectroscopy can serve as a valuable tool for quickly and reliably assessing variations in the amount and composition of organic matter in northern cold-region soils.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Julie D. Jastrow
Argonne National Laboratory
jdjastrow@anl.gov (630-252-3226)

(Corresponding Author Contact)
Roser Matamala
Argonne National Laboratory
matamala@anl.gov (630-252-9270)

Funding
This study was supported by the US Department of Energy, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Science Division, Terrestrial Ecosystem Science Program under contract DE-AC02-06CH11357 to Argonne National Laboratory.

Publications
Matamala, R., F.J. Calderón, J.D. Jastrow, Z. Fan, S.M. Hofmann, G.J. Michaelson, U. Mishra, C.L. Ping, “Influence of site and soil properties on the DRIFT spectra of northern cold-region soils.” Geoderma 305, 80-91 (2017). [doi:10.1016/j.geoderma.2017.05.014]. (Reference link)

Related Links
Argonne Terrestrial Ecosystem Science SFA

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 06, 2017

Terrestrial Biosphere Models Underestimate Photosynthetic Capacity and CO2 Assimilation in the Arctic

New measurements of photosynthesis in the Arctic demonstrate that current models underestimate key photosynthetic parameters and the potential for CO2 uptake by Arctic vegetation.

The Science
Carbon uptake and loss from the Arctic is highly sensitive to climate change and these processes are poorly represented in terrestrial biosphere models (TBMs). Uncertainty surrounding the Arctic carbon cycle is dominated by uncertainty over CO2 uptake by photosynthesis. However, current TBMs have almost no data on Arctic photosynthesis and currently rely on understanding developed in temperate systems. This study provided the first Arctic dataset of the key photosynthetic parameters maximum carboxylation capacity and maximum electron transport rate (known as Vcmax and Jmax, respectively). We found that current TBM representation of these two parameters was markedly lower than the values we measured on the coastal tundra of northern Alaska, in some case five-fold lower. On average, the capacity for CO2 uptake by Arctic vegetation is double current TBM estimates.

The Impact
This work highlights the poor representation of Arctic photosynthesis in terrestrial biosphere models and provides the critical data necessary to improve our ability to project the response of the Arctic to global environmental change.

Summary
We measured Vcmax and Jmax, in seven species representative of the dominant vegetation found on the coastal tundra near Barrow, Alaska. We made three key discoveries: (1) The temperature response functions of Vcmax and Jmax that are used to determine how the capacity for CO2 uptake changes with temperature were markedly different than the temperature response functions of temperate plants. (2) Vcmax (shown here in the figure) and Jmax were two to five- fold higher than the values used to parameterize current TBMs. (3) Current parameterization of TBMs resulted in a two-fold underestimation of the capacity for leaf level CO2 assimilation in Arctic vegetation. The insight and data set we provide in this study can be used to markedly improve TBM representation of Arctic photosynthesis and improve projections of how Arctic photosynthesis responds to rising temperature and CO2 concentration. The high impact dataset generated during this study has already been used in four additional publications.

Contacts
(BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Alistair Rogers
Brookhaven National Laboratory
arogers@bnl.gov

Funding
This work was funded by the Next-Generation Ecosystem Experiment (NGEE-Arctic) project. The NGEE-Arctic project is supported by the Office of Biological and Environmental Research in the Department of Energy, Office of Science.

Publications
Primary publication
Rogers A, Serbin SP, Ely KS, Sloan VL, Wullschleger SD (2017) Terrestrial biosphere models underestimate photosynthetic capacity and CO2 assimilation in the Arctic. New Phytologist.. Online Early. [doi: 10.1111/nph.14740] (Reference link)

Additional publications that used data from this study
Ghimire B, Riley WJ, Koven CD, Kattge J, Rogers A, Reich PB, Wright IJ (2017) A global trait-based approach to estimate leaf nitrogen functional allocation from observations. Ecological Applications. 27, 1421-1434.

De Kauwe MG, Lin Y-S, Wright IJ, Medlyn BE, Crous KY, Ellsworth DE, Maire V, Prentice IC, Atkin OK, Rogers A, Niinemets U, Serbin S, Meir P, Uddling J, Togashil HF, Tarainen L, Weerasinghe LK, Evans BJ, Ishida FY, Domingues TF (2016) A test of the "one-point method" for estimating carboxylation capacity from field-measured, light-saturated photosynthesis. New Phytologist. 210, 1130-1144.

Ali AA, Xu C, Rogers A, Fisher RA, Wullschleger SD, McDowell NG, Massoud EC, Vrugt JA, Muss JD, Fisher JR, Reich PB, Wilson CJ (2016) A global scale mechanistic model of photosynthetic capacity (LUNA V1.0). Geoscientific Model Development 9, 587-606.

Ali AA, Xu C, Rogers A, McDowell NG, Medlyn BE, Fisher R, Wullschleger SD, Reich PR, Vrugt JA, Bauerle WL, Santiago LS, Wilson CJ (2015) Global scale environmental control of plant photosynthetic capacity. Ecological Applications 25, 2349-2365.

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER





August 07, 2017

A Multi-Species Synthesis of Physiological Mechanisms in Drought-Induced Tree Mortality

The Science  
This is the first paper to synthesize the results on mechanisms of mortality from all known drought manipulation studies, and found that hydraulic failure is a universal component of death while carbon starvation is frequent but not universal.

The Impact
This paper 1) tests a contentious hypothesis regarding hydraulic failure and carbon starvation, for the first time, at a global scale, 2) provides modelers a direct path to improving vegetation dynamics simulations.

Summary
About half of carbon dioxide emissions are absorbed by plants, but this service is threatened by increasing frequency of hot droughts. One of the largest uncertainties in land surface modeling is how vegetation will respond to greater exposure to life-threatening droughts. One of the most contentious theories in ecology today regards the mechanisms of responses e.g., how plants regulate hydraulic failure and carbon starvation (if they even occur at all) during drought. Hydraulic failure is where plants experience partial or complete interruption of the water transporting xylem tissue function from stress induced embolisms that inhibits water transport, leading to desiccation. Carbon starvation is a phenomena where an imbalance between carbohydrate demand and supply leads to an inability to meet osmotic, metabolic and defensive carbon requirements. This study reviewed and synthesized the findings on all known drought studies that killed trees and found the occurrence of hydraulic failure was a universal characteristic proceeding plant death, and co-occurring carbon starvation occurred in approximately 50% of studies. The most advanced land-surface models today simulate mortality via carbon starvation but not via hydraulic failure. Therefore, current model development should incorporate hydraulic failure as a trigger to plant mortality to improve our understanding and predictions of ecosystems and vegetation.

Contacts
(BER PM)

Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Nate McDowell
Pacific Northwest National Lab
nate.mcdowell@pnnl.gov

Funding
Funding was provided by DOE, Office of Science, NGEE-Tropics, via the Los Alamos and the Pacific Northwest National Lab’s LDRD program, and via NSF.

Publications
Adams et al. (61 co-authors). A multi-species synthesis of physiological mechanisms in drought-induced mortality.. Nature Ecology & Evolution 1, 1285-1291 (2017). [doi:10.1038/s41559-017-0248-x] (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 25, 2017

Dual Role of Microorganisms in Soil Organic Matter Dynamics

Soil microbes function as both decomposers and synthesizers of soil organic matter.

The Science 
The concept of a soil “microbial carbon pump” is proposed as a mechanism for integrating how the contrasting breakdown and synthesis activities of microorganisms — coupled with the “entombment” of microbial residues via organo-mineral interactions — influence soil organic matter dynamics and persistence.

The Impact
A conceptual framework was developed to inspire new research aimed at the role of microorganisms in the formation of persistent soil organic matter. New understanding on this topic is essential for model development and for informing national and global discussions on the sustainability and vulnerability of soils, including related impacts on food and biofuel production, ecosystem services, environmental health, and climate.

Summary
The dynamic balance between inputs of organic materials versus losses (via decomposition or transport) regulates soil organic matter cycling. In this context, microbes are widely investigated as major mediators of decomposition, particularly through the effects of their extracellular enzymes. Less studied is the impact of microbial growth and death on the creation of soil organic matter. Because the living biomass of microbes in soil is small, microbial contributions to soil organic matter formation have been underappreciated. But, the rapid life cycle of microbes can produce large amounts of organic residues over time. Even though microbial residues can be intrinsically easy to decompose, recent studies suggest a significant portion can be stabilized in soils by intimate physical and chemical associations with soil minerals. In this perspective article, the contrasting metabolic roles that microbes play in soil organic matter dynamics (i.e., catabolic breakdown and anabolic formation) are reviewed. The concept of a soil “microbial carbon pump” is borrowed from marine literature and coupled with the “entombing effect” (stabilization via organo-mineral interactions) to create a framework for stimulating and guiding new research efforts targeted at the role of microbial synthesis and turnover in the formation of persistent soil organic matter.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(BER-funded PI Contact)
Julie D. Jastrow
Argonne National Laboratory
jdjastrow@anl.gov (630-252-3226)

(Lead PI Contact)
Chao Liang
Chinese Academy of Sciences
cliang823@gmail.com

Funding
This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research.

Publications
Liang, C., J.P. Schimel, & J.D. Jastrow, “The importance of anabolism in microbial control over soil carbon storage.” Nature Microbiology 2, 17105 (2017). [doi:10.1038/nmicrobiol.2017.105]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 24, 2017

FATES Integrations with ACME Model

Next-generation dynamic vegetation model integrated with ACME Land Model.

The Science  
FATES, a dynamic vegetation model that predicts tree size distributions, disturbance dynamics, and plant trait competition, has been integrated into the ACME Land Model, and released as an open source tool to the public.

The Impact
FATES will allow a richer representation of the potential ecosystem responses to weather, land-use, and atmospheric compositional changes, and how these ecosystem changes alter the dynamics of the Earth system. The coupled ACME ESM will benefit from these changes to allow it to be applied to scientific questions about the role of ecosystem change in the context of larger global changes.

Summary
The Functionally Assembled Terrestrial Ecosystem Simulator (FATES) is a demographic vegetation model that includes dynamics that are not included in the current ACME Land Model, such as individual tree growth, death, and competition for light; explicit representation of both natural and anthropogenic disturbance; and competitive dynamics between different plant functional types as a result of their differing plant traits. The FATES model has been designed for modularity to allow scientific isolation of component processes and clean scientific experimental design. Because FATES makes predictions about tree size distributions, disturbance dynamics, and physiological dynamics at the level of individual trees, it can be more robustly tested against field measurements and can therefore serve as an organizing model for DOE field activities, particularly in forested ecosystems, such as NGEE Tropics. Now that FATES has been fully integrated into the ACME Land Model, such activities are directly feeding into ACME science.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Dorothy Koch
SC-23.1
Dorothy.Koch@science.doe.gov (301-903-0105)

(PI Contact)
Charles Koven, Lawrence Berkeley National Laboratory
Phone: 510-486-6724
cdkoven@lbl.gov

Funding
Support for this activity is from the Department of Energy, Office of Science, Biological and Environmental Research, through the Climate and Environmental Sciences Division and the Terrestrial Ecosystem Sciences, Earth System Modeling and Climate Modeling Development and Validation programs as part of the Next-Generation Ecosystem Experiments (NGEE-Tropics) Project.

Related Links
FATES-release github repository

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 20, 2017

A Direct Measure of Basin-Wide Evaporation and Transpiration from the Amazon Rainforest

A water budget approach shows complex seasonal cycle and long-term changes in tropical forest function.

The Science  
The NGEE-Tropics research team combined satellite measurements of rainfall and gravity anomalies with Amazon River flow data to derive a seasonally-resolved estimate of evapotranspiration for the entire Amazon basin. Next the team analyzed the seasonal cycles and long-term variation of this measurement and compared it to process-based land surface model predictions.

The Impact
The study’s results show a more complex and different seasonal cycle than current land surface models predict. The study suggests a long-term decline in evapotranspiration from the forest, due to ecosystem functional change at the scale of the entire basin.

Summary
Evapotranspiration, which comprises the sum of all moisture fluxes from an ecosystem directly to the atmosphere, is a crucial quantity at the center of the terrestrial energy, water, and carbon cycles. Because measurements of evapotranspiration are typically made at local scales, and are sparse over remote locations such as the Amazon, the larger-scale fluxes are not well known. This study combined observations of rainfall, river discharge, and time-varying gravity anomalies to construct a water budget for the Amazon basin, which allows the NGEE-Tropics researchers to solve for evapotranspiration as the missing term in the budget. This water budget-based measurement shows a complex seasonal cycle, with a deeper minimum during the wet season than is estimated by other upscaling estimates or by process-based models, and also shows that models tend to increase their seasonal evapotranspiration fluxes later in the dry season than is observed. Furthermore, a long-term analysis of evapotranspiration suggests a decline in the rate over the period of observation, which could be evidence of a large-scale change in ecosystem function.

Contacts (BER PM)
Daniel Stover, Dorothy Koch, Renu Joseph
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)
dorothy.koch@science.doe.gov (301-903-0105)
Renu.Joseph@science.doe.gov (301-903-9237)

(PI Contact)
Charles Koven
Lawrence Berkeley National Laboratory
cdkoven@lbl.gov, 510.486.6724

Funding
ALSS was supported by National Science Foundation grants AGS-1321745 and AGS-1553715. CDK received support from the Regional and Global Climate Modeling program through the BGC-Feedbacks SFA and the Terrestrial Ecosystem Sciences and Earth System Modeling programs through the Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics) project of the Biological and Environmental Research (BER) Program in the U. S. Dept. of Energy Office of Science.

Publications
Swann, A. L. S., and Koven , C. D. A direct estimate of the seasonal cycle of evapotranspiration over the Amazon. Journal of Hydrometeorology (2017). [doi:10.1175/JHM-D-17-0004.1] (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 04, 2017

Variations of Leaf Longevity in Tropical Moist Forests Predicted by a Trait-driven Carbon Optimality Model

Here we develop a new model to capture large intraspecific variability in leaf longevity of 105 tropical tree species within two tropical moist forests in Panama.

The Science
Leaf longevity (LL), how long a leaf lives, is closely linked to plant resource use, carbon uptake, and growth strategy. In tropical forests, there is remarkable diversity in LL across species, ranging from several weeks to 6 years or more. However, it remains unclear how to capture such large variation using predictive models. Here, we present a meta-analysis of 49 species across temperate and tropical biomes. Our results show that the leaf ageing rate is positively correlated with the mass-based carbon uptake rate of mature leaves. We further developed a LL model to capture leaf aging rate and evaluated it with LL data for 105 species measured in two tropical forests in Panama. Our results show that the new model explains over 40% of the cross-species variation in LL, including those species sampled from both canopy and understory. Collectively, our results reveal how variation in LL is constrained by both leaf structural traits and the growth environment.

The Impact
Leaf longevity has been recognized as critical for understanding tropical seasonality and carbon dynamics. Our proposed leaf longevity model can be used in next generation Earth System Models (ESMs) to improve projections of carbon dynamics and potential climate feedbacks in the tropics.

Summary
We use a trait-based carbon optimality approach to model leaf longevity (LL, in days), and assess the model performance with in-situ LL data for 105 species in two tropical forests in Panama. More specifically, we examine the relative impact of leaf ageing rate (i.e. the rate at which leaf photosynthetic capacity declines with age) and within-canopy variation in light environment on the modeled LL. We first assumed that all species have the same leaf ageing rate (i.e. the community average value) and receive the same light condition (i.e. canopy-level light), and the results are shown in panel a, with a correlation coefficient r=0.08 which is not significant. Then we performed the analysis with species-specific leaf ageing rates, while assuming that all species receive the same light condition (i.e. canopy-level light), and the results are shown in panel b, with r=0.53 and p-value<<0.001. We lastly performed the analysis with species-specific leaf ageing rate and light environment, and the results are shown in panel c, with r=0.66 and p-value <<0.001. Our results thus suggest that both leaf aging rate and within-canopy variation in light environment are essential for modeling LL in the tropics, and the best model can capture over 40% of interspecific variability in LL, including those species from canopy and understory.  

Contacts
(BER PM)

Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Dorothy Koch
SC-23.1
Dorothy.koch@science.doe.gov (301-903-0105)

(PI Contact)
Lead author contact information
Jin Wu
Brookhaven National Laboratory 
jinwu@bnl.gov 

Institutional contact
Alistair Rogers
Brookhaven National Laboratory
arogers@bnl.gov

Funding
J. Wu was supported by the Next-Generation Ecosystem Experiment (NGEE-Tropics) project. The NGEE-Tropics project is supported by the Office of Biological and Environmental Research in the Department of Energy, Office of Science.

Publications
Xu X, Medvigy D, Wright SJ, Kitajima K, Wu J, Albert LP, Martins GA, Saleska SR, Pacala SW. Variations of leaf longevity in tropical moist forests predicted by a trait-driven carbon optimality model. Ecology Letters, 2017.[doi:10.1111/ele.12804] (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


June 23, 2017

Global Photosynthesis Modeling is Stymied by Competing Hypotheses on Scaling of Plant Traits

Uncertainty in how maximum photosynthetic rates scale across the Earth leads to substantial uncertainty predictions of terrestrial carbon uptake.

The Science
A major source of uncertainty in modeling of global photosynthesis and associated carbon cycle dynamics, is the calculation of maximum photosynthetic carboxylation rate, which is one of two plant traits that closely determines photosynthetic rate. Various methods are used in terrestrial biosphere models to calculate these traits; each representing a different theory about how these traits scale but the resultant errors have not yet been quantified.

The Impact
This research highlights the need for robust estimates of global photosynthesis and a better understanding of how maximum photosynthetic rates scale across the Earth’s surface.

Summary
The impact on global patterns of photosynthesis of four trait-scaling hypotheses (plant functional type, nutrient limitation, environmental filtering, and plant plasticity) was investigated by an international team of researchers. Led by a DOE researcher at Oak Ridge National Laboratory, the study finds that global photosynthesis estimates from the different trait-scaling hypotheses ranged between 108 and 128 PgC yr-1, representing around 65% of the uncertainty range found in photosynthesis model intercomparison exercises. The uncertainty propagated through to a 27% variation in net biome productivity, the net amount of carbon removed from the atmosphere by land ecosystems. All hypotheses produced global photosynthesis estimates that were highly correlated with proxies of global photosynthesis. Nevertheless, nutrient limitation appeared to be marginally the best method to simulate the scaling of maximum photosynthetic rates. The comparison of model photosynthesis with ‘observed’ photosynthesis was stymied by the fact that no robust methods exist to measure photosynthesis at the global scale. For this reason, researchers used three proxies of global photosynthesis to compare with the model estimates. Interestingly, photosynthesis in agricultural regions of Earth were much higher in the satellite-based photosynthesis proxies that measure solar induced fluorescence of the photosynthetic machinery in a leaf. Higher photosynthesis in these regions when measured from space suggest that models and other photosynthesis proxies may be missing an important component of global photosynthesis in these managed ecosystems. 

Contacts
(BER PM)

Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289) 

Dorothy Koch
SC_23.1
Dorothy.koch@science.doe.gov (301-903-0105)

(PI Contact)
Anthony P. Walker
Oak Ridge National Laboratory
walkerap@ornl.gov

Funding
DOE Office of Science BER, Next Generation Ecosystem Experiments — Tropics

Publications
Walker, A. P. et al. The impact of alternative trait-scaling hypotheses for the maximum photosynthetic carboxylation rate (Vcmax) on global gross primary production. New Phytol Early View (2017). [doi:10.1111/nph.14623] (Reference link)

Related Links
Next Generation Ecosystem Experiments — Tropics

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


June 22, 2017

A Direct Measure of Basin-Wide Evaporation and Transpiration from the Amazon Rainforest

A water budget approach shows complex seasonal cycle and long-term changes in tropical forest function.

The Science 
The Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics) research team combined satellite measurements of rainfall and gravity anomalies with Amazon river flow data to derive a seasonally-resolved estimate of evapotranspiration for the entire Amazon basin.  The team then analyzed the seasonal cycles and long-term variation of this measurement, and compared it to process-based land surface model predictions.

The Impact
The study’s results show a more complex and different seasonal cycle than current land surface models predict. The study suggests a long-term decline in evapotranspiration from the forest, due to ecosystem functional change at the scale of the entire basin.

Summary
Evapotranspiration, which comprises the sum of all moisture fluxes from an ecosystem directly to the atmosphere, is a crucial quantity at the center of the terrestrial energy, water, and carbon cycles. Because measurements of evapotranspiration are typically made at local scales, and are sparse over remote locations such as the Amazon, the larger-scale fluxes are not well known. This study combined observations of rainfall, river discharge, and time-varying gravity anomalies to construct a water budget for the Amazon basin, which allows NGEE-Tropics researchers to solve for evapotranspiration as the missing term in the budget. This water budget-based measurement shows a complex seasonal cycle, with a deeper minimum during the wet season than is estimated by other upscaling estimates or by process-based models, and also shows that models tend to increase their seasonal evapotranspiration fluxes later in the dry season than is observed. Furthermore, a long-term analysis of evapotranspiration suggests a decline in the rate over the period of observation, which could be evidence of a large-scale change in ecosystem function.

Contacts (BER PM)
Daniel Stover, Dorothy Koch, Renu Joseph
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)
dorothy.koch@science.doe.gov (301-903-0105)
Renu.Joseph@science.doe.gov  (301-903-9237)

(PI Contact)
Charles Koven
Lawrence Berkeley National Lab
cdkoven@lbl.gov, 510.486.6724

Funding
ALSS was supported by National Science Foundation grants AGS-1321745 and AGS-1553715. CDK received support from the Regional and Global Climate Modeling program through the BGC-Feedbacks SFA and the Terrestrial Ecosystem Sciences and Earth System Modeling programs through the Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics) project of the Biological and Environmental Research (BER) Program in the U. S. Dept. of Energy Office of Science.

Publications
Swann, A. L. S., and C. D. Koven. 2017. “A direct estimate of the seasonal cycle of evapotranspiration over the Amazon.” Journal of Hydrometeorology doi:10.1175/JHM-D-17-0004.1 (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


June 22, 2017

International Space Station Observations Offer Insights into Plant Function

New instrumentation will be installed on the International Space Station to provide a unique opportunity to gain important insights into poorly understood ecosystems.

The Science  
Ecosystems, particularly tropical forests, play an important role in determining the rate and extent of changes in the Earth system by absorbing and storing about one-third of the carbon dioxide released when we use fossil fuels. Our current understanding of how ecosystems take up and store carbon dioxide is limited to those areas that can be reached by scientists, yet these study sites represent only a small fraction of the total land area. New instrumentation and technology offer the opportunity to remotely measure many important properties of plants and ecosystems that will help determine how the planet will respond to changing environments and provide critical data for testing models of ecosystem response to a changes in the Earth system. Specifically, remote measurement of tree height, temperature, carbon dioxide uptake and biochemical composition offers exciting new opportunities for science. This work highlights the deployment of new instrumentation on the international space station (ISS), informs the scientific community of the opportunity presented by these measurements, and describes ways to use this unique data. The work is the result of detailed discussions and an ongoing collaboration between ecosystem modelers, experimentalists, and remote sensing scientists.

The Impact
This paper provides a clear vision on the ways in which the experimental, modeling, and remote sensing communities can use simultaneous observations of ecosystem structure, function, composition, and biochemistry from a suite of novel sensors that will be installed on the International Space Station (ISS). Importantly, the collection of these remotely sensed data will improve our understanding of ecosystems as well as our ability to test predictive models.

Summary
To improve prediction of the ability of plants to slow the rate of Earth and environmental change by absorbing and storing carbon dioxide, scientists need more data about the composition, function, and structure of terrestrial ecosystems, particularly in remote regions such as the tropics. Unfortunately, our current ability to measure and understand important ecosystem processes is too sparse, and too spatially biased to make significant progress. Satellite observations are the only source for the required dense, frequent, spatially and temporally extensive records. The unique collection of measurements anticipated from the ISS will yield important new insights into ecosystem structure and function and provide important new observations to evaluate the models we use to understand how important ecosystems, such as tropical forests, will respond to changing conditions.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
BER funded PI
Shawn Serbin  
Brookhaven National Laboratory
sserbin@bnl.gov

Lead PI
Natasha Stavros
NASA JPL
Natasha.Stavros@jpl.nasa.gov

Funding
S.P. Serbin was supported by the Next-Generation Ecosystem Experiment (NGEE-Tropics) project. The NGEE-Tropics project is supported by the Office of Biological and Environmental Research in the Department of Energy, Office of Science.  The Exploring New Multi-Instrument Approaches to Observing Terrestrial Ecosystems and the Carbon Cycle from Space workshop and participant travel costs were supported by the W. M. Keck foundation.

Publications
Stavros, N.E., D. Schimel, R. Pavlick, S.P. Serbin, A. Swann, L. Duncanson, J. B. Fisher, F. Fassnacht, S. Ustin, R. Dubayah, A. Schweiger, and P. Wennberg. 2017. “ISS observations offer insights into plant function.” Nature Ecology and Evolution, (1), 01974. DOI: 10.1038/s41559-017-0194. (Reference link)

Related Links
Keck workshop 
S. Serbin (DOE-TES) workshop talk & video

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


June 20, 2017

A Metadata Reporting Framework (FRAMES) for Synthesis of Ecohydrological Observations

A metadata reporting framework (FRAMES) for synthesis of ecohydrological observations.

The Science 
FRAMES is a set of Excel and on-line templates that standardize reporting of diverse ecohydrological data and the necessary metadata required for data synthesis to study earth systems.

The Impact
Detailed metadata, information that describes when, where, and how data is generated, is required for interpreting, comparing, validating, and synthesizing ecohydrological observations collected with diverse methods in different ecosystems. FRAMES bridges the gap between complex data information models that are needed to organize detailed metadata and specific ecohydrological data reporting protocols that lack enough detail for earth system science research.

Summary
FRAMES templates standardize reporting of diverse ecohydrological data and metadata for data synthesis required for earth system science research. We developed FRAMES iteratively with data providers and consumers who are developing a predictive understanding of carbon cycling in the tropics. Key features include: (1) Best data science practices; (2) Modular design that allows for addition of new measurement types; (3) Data entry formats that enable efficient reporting; (4) Multiscale hierarchy that links observations across spatiotemporal scales; and (5) Collection of metadata for integrating data with earth system models.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Dorothy Koch
SC-23.1
Dorothy.Koch@science.doe.gov (301-903-0105)

(PI Contacts)
Danielle S. Christianson
Lawrence Berkeley National Laboratory
dschristianson@lbl.gov

Charuleka Varadharajan
Lawrence Berkeley National Laboratory
cvaradharajan@lbl.gov

Funding
Research supported by Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics), funded by U. S. Department of Energy, Office of Science, Office of Biological and Environmental Research.

Publications
D.S. Christianson, C. Varadharajan, B. Christoffersen, M. Detto, B. Faybishenko, B.O. Gimenez, V. Hendrix, K. J. Jardine, R. Negron-Juarez, G.Z. Pastorello, T.L. Powell, M. Sandesh, J.M. Warren, B.T. Wolfe, J.Q. Chambers, L.M. Kueppers, N.G. McDowell, D.A. Agarwal, “A metadata reporting framework (FRAMES) for synthesis of ecohydrological observations.” Ecological Informatics (2017). [DOI: 10.1016/j.ecoinf.2017.06.002] (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


June 10, 2017

Do Dynamic Global Vegetation Models Capture the Seasonality of Carbon Fluxes in the Amazon Basin? A Data-Model Intercomparison

Seasonal Carbon Fluxes in Amazon Forests.

The Science  
We compared and contrasted the observed and modeled seasonality of ecosystem photosynthesis (GPP), leaf, and wood production (NPPleaf, NPPwood) at four sites across the Amazon basin spanning dry season lengths of 1 to 6 months. Observations came from a network of eddy covariance towers and associated ground-based measurements; models were IBIS, ED2, JULES, and CLM3.5, many of which are used in coupled climate-carbon cycle simulations.

The Impact
Observations in Amazonian forests consistently show that seasonality in GPP is driven by endogenous biological cycles of leaf flushing and associated age-related trends in leaf-level photosynthetic capacity. This intercomparison makes an important link between model deficiencies in seasonal carbon flux dynamics with the missing biological mechanisms driving photosynthesis and leaf and stem growth in seasonal Amazon forests. It therefore guides model development with these seasonal carbon flux benchmarks, and by highlighting leaf age and carbon sink limitation as key mechanisms underlying these patterns.

Summary
Using dynamic global vegetation models (DGVMs) for prediction requires that they be successfully tested against ecosystem response to short-term variations in environmental drivers, including regular seasonal patterns. In this data-model intercomparison of DGVMs and observations of carbon fluxes at four forests in the Amazon basin, we found that most DGVMs poorly represented the annual cycle of gross primary productivity (GPP), of photosynthetic capacity (Pc), and of leaf and stem growth. Because these mechanisms are absent from models, modeled GPP seasonality usually follows that of soil moisture availability, which only agrees with observations at the driest, southernmost site. Furthermore, observations suggest that seasonality in growth (NPP) arises from lags or other processes limiting the allocation of GPP to leaves and stems, mechanisms also absent from models. Correctly simulating flux seasonality at tropical forests requires a greater understanding and the incorporation of internal biophysical mechanisms in future model developments.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Brad Christoffersen
Los Alamos National Laboratory
bradley@lanl.gov, 505-665-9118 

Funding
This research was funded by the Gordon and Betty Moore Foundation ‘Simulations from the Interactions between Climate, Forests, and Land Use in the Amazon Basin: Modeling and Mitigating Large Scale Savannization’ project and the NASA LBADMIP project (NNX09AL52G). N.R.C. acknowledges the Plant Functional Biology and Climate Change Cluster at the University of Technology Sydney, the National Aeronautics and Space Administration (NASA) LBA investigation CD-32, the National Science Foundation’s Partnerships for International Research and Education (PIRE) (OISE-0730305). B.O.C. and J.W. were funded in part by the US DOE (BER) NGEE-Tropics project to LANL and by the Next-Generation Ecosystem Experiment (NGEE-Tropics) project from the US DOE, Office of Science, Office of Biological and Environmental Research and through contract DESC00112704 to Brookhaven National Laboratory, respectively.

Publications
Restrepo-Coupe, N. et al. Do dynamic global vegetation models capture the seasonality of carbon fluxes in the Amazon basin? A data-model intercomparison. Global Change Biology 23, 191-208, doi:10.1111/gcb.13442 (2017). (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 29, 2017

Ecological Role of Hydraulic Traits of Amazon Rainforest Trees

Differences in xylem and leaf hydraulic traits explain differences in drought tolerance among mature Amazon rainforest trees

The Science 
This study demonstrated that tropical tree species that were tolerant of an experimental drought had hydraulic traits that differed from those that were intolerant.  The hydraulic traits of the measured species were not aligned with their early- versus late-successional life histories, thus revealing an important drought-tolerance control over tropical forest dynamics.

The Impact
The observed differences in plant hydraulic traits enhances our understanding of important controls over tropical forest dynamics, which is critical for informing the parameterization of hydrodynamic formulations used in Earth System Models.

Summary
This study found a characteristic pattern in the measured leaf and xylem traits of several tropical tree species that was consistent with their demographic responses to an experimentally-imposed drought.  This study provides valuable insight into the traits controlling drought tolerance of tropical rainforest trees and provides much needed information for parameterizing more realistic water-stress functions in Earth System Models. Finally, understanding the variability in plant hydraulic traits that exists among tropical tree species is critical for determining the fate of the Amazon rainforest if precipitation patterns change substantially.

Contacts (BER PM)
Daniel Stover and Dorothy Koch
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289); dorothy.koch@science.doe.gov (301-903-0105)

(PI Contact)
Thomas L. Powell
Lawrence Berkeley National Laboratory
tlpowell@lbl.gov

Funding
This research was funded by a National Science Foundation Doctoral Dissertation Improvement Grant (NSF award # DEB-1110540), the National Science Foundation Partnership for International Research and Education in Amazon Climate Interactions grant (NSF award #OISE-0730305), a grant from the Andes-Amazon Initiative of The Gordon and Betty Moore Foundation, graduate research funding from the Department of Organismic and Evolutionary Biology, Harvard University, and the Office of Biological and Environmental Research, US Department of Energy, NGEE-Tropics grant.  Patrick Meir was supported by NERC NE/J011002/1 and ARC FT110100457.

Publications
Powell T.L., Wheeler J.K., de Oliveira  A.A.R., da Costa A.C.L., Saleska S.R., Meir P., Moorcroft P.R. Differences in xylem cavitation resistance and leaf hydraulic traits explain differences in drought tolerance among mature Amazon rainforest trees. Global Change Biology (2017). DOI: 10.1111/gcb.13731 (Reference link)

Powell T., Moorcroft P. Leaf Pressure Volume Data in Caxiuanã and Tapajós National Forest, Para, Brazil (2011). NGEE Tropics Data Collection. Accessed at http://dx.doi.org/10.15486/NGT/1347606

Powell T., Moorcroft P. Xylem vulnerability curves of canopy branches of mature trees from Caxiuanã and Tapajós National Forests, Para, Brazil. NGEE Tropics Data Collection. Accessed at http://dx.doi.org/10.15486/NGT/1347607

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 27, 2017

Long Term Decomposition: The Influence of Litter Type and Soil Horizon on Retention of Plant Carbon and Nitrogen in Soils

Litter type affects initial decomposition rates, but soil horizon affects mechanisms of long-term soil carbon stabilization.

The Science 
In one of the few studies examining litter decay over a decade, Berkeley scientists used stable isotope labels to trace plant litter-derived carbon and nitrogen as litter decomposed and formed soil organic matter. They found that the litter type (needles or roots) and the soil environment (organic or mineral horizon) both affected decomposition, but at different timescales.

The Impact
This research helps bridge the gap between studies of litter decomposition and soil organic matter by tracing how litter becomes soil organic matter over a decade. The results back the recent paradigm shift in our understanding of soil carbon research by demonstrating that the long-term retention of litter-derived carbon and nitrogen soil is an ecosystem property dependent on the soil horizon in which the litter was placed.

Summary
We found that the legacy of the type of plant inputs (root or needle litter) affected total C and N retention over 10 years, but that soil horizon affected how the litter-derived SOM is stabilized in the long term. In the organic (O) horizon, litter was retained in the coarse particulate size fraction (>2 mm) over 10 years, likely due to conditions that limited its physical breakdown. In the mineral (A) horizon, litter-derived C and N were retained in a finer size fraction (<2 mm), likely due to association with minerals that prevent microbes from accessing the C and N. Litter type had no effect on the stabilization of litter-derived C and N in mineral-associated pools. After 10 years, 5% of initial C and 15% of initial N were retained in organo-mineral associations, which form the most persistent organic matter in soils. Very little litter-derived C moved vertically in the soil profile over the decade, but N was significantly more mobile.

Contacts (BER PM)
Dan Stover, TES Program Manager
301-903-0289
daniel.stover@science.doe.gov

PI Contact
Margaret S. Torn
Lawrence Berkeley National Laboratory
mstorn@lbl.gov

Funding
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program under contract number DE-AC02-05CH11231.

Publications
Hicks Pries C, JA Bird, C Castanha, PJ Hatton, and MS Torn. 2017. Long term decomposition: the influence of litter type and soil horizon on retention of plant carbon and nitrogen in soils. Biogeochemistry. doi:10.1007/s10533-017-0345-6 (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 23, 2017

Amazonian Forest Isoprene Emissions Vary with Terrain Elevations

Research identifies a key factor governing the variability of isoprene emissions over the Amazonian forest.

The Science
Isoprene dominates global non-methane volatile organic compound (VOC) emissions and impacts tropospheric chemistry by influencing oxidants and aerosols (small atmospheric particles). This work, performed by a team including Department of Energy (DOE) scientists and DOE’s Atmospheric Radiation Measurement (ARM) Aerial Facility, identifies for the first time a key factor that governs isoprene emission rates within the Amazonian forest. Analyzing aircraft eddy covariance measurements during the GoAmazon 2014-5 field campaign, this research finds that isoprene emissions strongly correlate with terrain elevations, most likely due to varying plant species distributions at different elevations. These findings are consistent with similar correlations derived from analysis of satellite data.

The Impact
This work demonstrates the value of aircraft-derived measurements during the DOE-supported GoAmazon 2014-2015 field campaign and produces new insights on the isoprene emissions rate. The findings provide key clues for improving the representation of isoprene emissions within regional and global Earth system models (ESMs). The study demonstrates that current modeling estimates of isoprene emissions may be too low over the Amazonian forest, especially during the dry season.

Summary
Isoprene is the most abundant short-lived, reactive VOC emitted by terrestrial vegetation and therefore affects the oxidation capacity of the atmosphere, the formation of ozone, and production of secondary organic aerosols (SOAs). Accurate model representation of isoprene emission rates is critical to understand global impacts on regional chemistry and aerosols. The research analyzed eddy covariance measurements based on a proton-transfer reaction mass spectrometry (PTR-MS) instrument onboard the Gulfstream-1 research aircraft, and showed that levels of isoprene emissions strongly correlate with terrain elevation, a finding not presently represented in current ESMs. The study also analyzed results from the regional Weather Research and Forecasting coupled with Chemistry (WRF-Chem) model that uses simple mechanistic algorithms to estimate biogenic emissions fluxes based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN). The research showed that the model underestimates isoprene emissions fluxes by ~35% compared to aircraft-derived estimates. Furthermore, these observations showed that biogenic isoprene emissions are much higher during the dry season compared to the wet season over the Amazonian forest. The study highlights the need for further measurements of leaf and canopy-scale isoprene emissions—at multiple sites along elevation gradients—to determine the cause and generality of these findings in other geographic locations.

Contacts (BER PM)
Ashley Williamson and Shaima Nasiri
Atmospheric System Research Program
Ashley.Williamson@science.doe.gov and Shaima.Nasiri@science.doe.gov

Sally McFarlane
Atmospheric Radiation Measurement Climate Research Facility
Sally.McFarlane@science.doe.gov

(PI Contact)
Jerome Fast
Pacific Northwest National Laboratory
Jerome.Fast@pnnl.gov

Funding
Institutional support was provided by the Central Office of the Large-Scale Biosphere Atmosphere Experiment in Amazonia (LBA), the (Brazilian) National Institute of Amazonian Research and National Institute for Space Research, Amazonas State University, and Brazilian Space Agency. The work was conducted for the Brazilian National Council for Scientific and Technological Development. We acknowledge the Atmospheric Radiation Measurement (ARM) Climate Research Facility, a user facility of the U.S. Department of Energy, Office of Science, sponsored by the Office of Biological and Environmental Research (BER), and support from BER’s Atmospheric System Research (ASR) program. A.B.G. was partially supported by the National Aeronautics and Space Administration’s Atmospheric Composition Campaign Data Analysis and Modeling program.

Publication
Gu, D., et al. 2017. “Airborne Observations Reveal Elevational Gradient in Tropical Forest Isoprene Emissions,” Nature Communications 8(15541), DOI: 10.1038/ncomms15541. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 08, 2017

Tundra Carbon Losses With Rapid Permafrost Thaw

Non-linear CO2 flux response to seven years of experimentally induced permafrost thaw.

The Science 
Frozen in permafrost soil northern latitudes store almost twice as much carbon as is currently in the atmosphere. Rapid Arctic warming is expected to expose previously frozen soil carbon to microbial decomposition and increase CO2 release to the atmosphere. The impact of permafrost thaw on the CO2 balance is however unclear because warmer temperatures and nutrients released from thawing permafrost also increase plant growth and could offset CO2 losses. We used an experimental warming manipulation to distinguish the effect of warmer air temperature from the effect of warmer soil and permafrost thaw on tundra ecosystem CO2 uptake and loss.

The Impact
Models and observations currently disagree over how Arctic warming will affect the CO2 balance of tundra ecosystems and few studies combine warmer air temperatures and permafrost thaw to evaluate ecosystem CO2 balance. This work demonstrates that tundra CO2 uptake and loss responded much more strongly to permafrost thaw than to warmer air temperatures alone. Rapid permafrost thaw did initially stimulate CO2 uptake during the summer, but leveled off with very deep thaw. In all years of the experiment, summer CO2 uptake was insufficient to offset year-round CO2 losses.

Summary
Seven years of experimental air and soil warming in tundra show that soil warming and permafrost thaw had a much stronger effect on carbon balance than air warming. Permafrost thaw initially stimulated greater summer CO2 uptake than CO2 loss, however the initial increases were not sustained. As thaw continued to progress, summer CO2 uptake and CO2 loss leveled off. Leveling off CO2 uptake and release could be explained by slowing of plant growth and greater soil saturation as thaw caused the ground surface to collapse. The complex interactions between permafrost thaw, plant growth, and soil moisture could be captured mathematically by a quadratic relationship showing that the effect of thaw on CO2 uptake and loss changed over time. Models and measurements used to estimate CO2 losses during the winter found that the tundra was losing CO2 on an annual basis, even during those summers when thaw stimulated high plant growth and CO2 uptake.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289) and Jared.DeForest@science.doe.gov (301-903-1678)

(PI Contact)
Ted Schuur
Northern Arizona University, Center for Ecosystem Science and Society (ECOSS)
ted.schuur@nau.edu

Funding
This work was supported by US Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Science Program (DE-SC0006982 and DE-SC0014085); National Science Foundation CAREER program (#0747195); National Science Foundation Bonanza Creek LTER program (#1026415); National Science Foundation Office of Polar Programs (#1203777); National Parks Inventory and Monitoring Program.

Publications
[Mauritz, M. et al. Nonlinear CO2 flux response to 7 years of experimentally induced permafrost thaw. Global Change Biology (2017), doi:10.1111/gcb.13661. (Reference link)

Related Links
Schuur Lab - Ecosystem Dynamics Research
Data Interpretation: Carbon balance in an Arctic Warming Manipulation

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 06, 2017

Flooding Determines Seasonality in Sphagnum Moss Photosynthesis

Identifying causes of seasonality in Sphagnum mosses at the SPRUCE experiment at the Marcell Experimental Forest, Minn.

The Science  
Sphagnum mosses form many of the world’s peat bogs, which store huge reservoirs of submerged carbon. These ecosystems are at risk in a changing climate. DOE researchers investigated how photosynthesis in Sphagnum mosses changes though the seasons at the Marcell Experimental Forest, Minn. Researchers were surprised to find that the peak in Sphagnum photosynthesis was delayed compared with the seasonal peak in sunlight strength and showed that the delayed peak was likely due to flooding of the Sphagnum and submergence by water suppressing photosynthesis.

The Impact
The influence of flooding on the seasonal cycle of Sphagnum photosynthesis is an advance in our understanding of these at risk ecosystems that will help improve model simulations under a changing environment.

Summary
Sphagnum mosses are the keystone species of peatland ecosystems. With rapid rates of climate change occurring in high latitudes, vast reservoirs of carbon accumulated over millennia in peatland ecosystems are potentially vulnerable to rising temperature and changing precipitation. DOE researchers investigated the seasonal drivers of Sphagnum photosynthesis—the entry point of carbon into wetland ecosystems. Continuous measurements of Sphagnum carbon exchange with the atmosphere show a seasonal cycle of Sphagnum photosynthesis that peaked in the late summer, well after the peak in photosynthetically active radiation. Statistical analysis of oscillations in the data showed that water table height was the key driver of weekly variation in Sphagnum photosynthesis in the early summer and that temperature was the primary driver of GPP in the late summer and autumn. A process-based model of Sphagnum photosynthesis was used to show the likelihood of seasonally changing maximum rates of photosynthesis and a previously unreported relationship between the water table and photosynthesising tissue area when the water table was at the Sphagnum surface. The model also suggested that variability in CO2 transport through the Sphagnum tissue to the site of photosynthetic fixation, caused by changing Sphagnum water content, had minimal effect on photosynthesis. Researchers came up with a list of four specific areas to improve the modeling of Sphagnum photosynthesis.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Anthony P. Walker
Oak Ridge National Laboratory
walkerap@ornl.gov

Funding
DOE Office of Science Office of Biological and Environmental Research, supports the Oak Ridge National Laboratory Terrestrial Ecosystem Science Scientific Focus Area.  

Publications
Walker, A. P. et al. Biophysical drivers of seasonal variability in Sphagnum gross primary production in a northern temperate bog. J. Geophys. Res. Biogeosci. 2016JG003711 (2017). [doi:10.1002/2016JG003711] (Reference link)

Related Links
Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) experiment
Data from this study http://mnspruce.ornl.gov/node/648

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 18, 2017

The Phenology of Leaf Quality and Its Variation are Essential for Accurate Modeling of Photosynthesis in Tropical Evergreen Forests

Here we develop a path for the representation of tropical photosynthetic seasonality in terrestrial biosphere models.

The Science  
The annual variation in tropical photosynthetic CO2 assimilation is about half the size of the terrestrial carbon sink and is therefore an important phenomenon to represent in terrestrial biosphere models (TBMs).  Three components of leaf phenology (i.e. quantity, quality, and within-canopy variation) all regulate tropical forest photosynthesis, but are absent or poorly represented in most TBMs. Here, we demonstrate how these three biological components can be integrated in a mechanistic representation of tropical evergreen forest photosynthetic seasonality. We show that the photosynthetic seasonality was not sensitive to leaf quantity, but was highly sensitive to leaf quality and its within-canopy variation, with markedly more sensitivity to upper canopy leaf quality. Our work thus highlights the importance of incorporating more realistic phenological mechanisms in TBMs that seek to improve the projection of future carbon dynamics in tropical evergreen forests.

The Impact
This study has three important implications for the broader ecology, plant physiology, and modeling communities. (1) Our work demonstrates that an improved and prognostic understanding and model representation of tropical leaf phenology will be a key component in new models that seek to improve projections of carbon dynamics and potential climate feedbacks in the tropics. (2) By isolating biological drivers of photosynthesis from weather, our work highlights the need to improve our understanding and model representation of the fundamental physiological response to environmental variability in the tropics. (3) Our work also highlights the data paucity in the tropics that currently limits our ability to test and evaluate the proposed model framework at broader scales.

Summary
The average annual cycle of canopy photosynthesis (i.e. Gross Primary Productivity, GPP) under a reference environment, GPPref (i.e. an indicator of canopy integrated photosynthetic capacity), of a central Amazonian evergreen forest in Brazil was derived from eddy covariance (EC) measurements (years 2002-2005 and 2009-2011; black lines). Here we used a two-fraction leaf (sun vs. shade), two-layer (upper vs. lower) canopy model to examine the effects of three phenological components (i.e. quantity, quality, and within-canopy variation) on modeled GPPref. The model incorporating only the effect of “leaf quantity” is shown in yellow line, which does not follow EC-derived GPPref seasonality. The model incorporating the joint effects of “leaf quantity and leaf quality” is displayed in the blue line, which tracks the pattern of EC-derived GPPref seasonality, but only captures ~1/2 of the relative annual change. The model incorporating the effects from all three phenological components (i.e. quantity, quality, and within-canopy variation, approximated by ftop) is shown in green line, and tracks EC-derived GPPref seasonality in both phase and the relative annual change. Our results thus suggest that the phenology of leaf quality and its within-canopy variation are essential for accurate photosynthetic modeling in tropical evergreen forests.

Contacts (BER PM)
Daniel Stover
Terrestrial Ecosystem Science Program Manager
Daniel.Stover@science.doe.gov

(PI Contact)
Lead author contact
Jin Wu 
Brookhaven National Laboratory 
jinwu@bnl.gov  
Institutional contact
Alistair Rogers
Brookhaven National Laboratory
arogers@bnl.gov

Funding
J. Wu, SP Serbin, and A Rogers were supported by the Next-Generation Ecosystem Experiment (NGEE-Tropics) project. The NGEE-Tropics project is supported by the Office of Biological and Environmental Research in the Department of Energy, Office of Science.

Publication
Wu J, Serbin SP, Xu X, Albert LP, Chen M, Meng R, Saleska SR, Rogers A. The phenology of leaf quality and its within-canopy variation are essential for accurate modeling of photosynthesis in tropical evergreen forests. Global change biology, 2017, doi:10.1111/gcb.13725. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 17, 2017

The FLUXNET2015 Dataset

A new dataset to keep a sharper eye on land-air exchanges

The Science  
FLUXNET2015 is the largest and most complete dataset of land-atmosphere fluxes ever produced, including data from 212 sites from 30 countries. The FLUXNET and DOE AmeriFlux Management Project teams created the dataset, in a large-scale collaborative endeavor with regional networks and site teams from around the world.

The Impact
The data and derived products in the FLUXNET2015 dataset are consistently quality controlled and gap-filled, made simple to use, and can be used to validate satellite measurements, inform earth system models, provide insight into ecology and hydrology questions — as well as fuel novel applications, many harnessing big data tools, from the scales of microbes to continents. As an indication of the expected impact of this data release, only one year after its first announcement, the FLUXNET2015 dataset had been downloaded by more users than the previous release in the entirety of its nearly 10 years lifetime. In its first 15 months, FLUXNET2015 has had over 87,000 site-data downloads, more than twice the total number for the previous release (LaThuile2007: 41,000). Many factors contribute to the high scientific demand, including the enhanced derived products and long time-series in the dataset as well as growing emphasis on confronting data with models, more advanced data tools, and a more open data policy.

Summary
In the mid 1990s, regional networks like AmeriFlux and the European Fluxes Database were established to enable sharing of data and methods from measuring carbon, energy, and water exchanges between land and the atmosphere. FLUXNET brought these networks together, and allowed the creation of global synthesis datasets: the Marconi dataset in 2000, the LaThuile Dataset in 2007, and now the FLUXNET2015 dataset. These datasets were key to answering science questions on themes ranging from soil microbiology to the global carbon cycle. Among the new features for FLUXNET2015 are intensive data quality checks; energy corrections applied to achieve energy balance closure, potentially making the data more useful to climate and ecosystem models requiring closed energy budget; estimation of uncertainties for processing steps, leading to uncertainty quantification suitable for use in data-model integration; and improved accuracy of gap-filled data and aggregated products (e.g., daily or yearly sums) through use of downscaled ERA-Interim reanalysis data.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289

(PI Contact)
Margaret S. Torn
Lawrence Berkeley National Laboratory
mstorn@lbl.gov

Funding
Funding for the AmeriFlux Management Project was provided by the U.S. Department of Energy's Office of Science under Contract No. DE-AC02-05CH11231.

Funding for the FLUXNET Partnership Project was provided by the U.S. Department of Energy's Office of Science.

This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Other acknowledgments
This work used eddy covariance data acquired and shared by the FLUXNET community, including these networks: AmeriFlux, AfriFlux, AsiaFlux, CarboAfrica, CarboEuropeIP, CarboItaly, CarboMont, ChinaFlux, Fluxnet-Canada, GreenGrass, ICOS, KoFlux, LBA, NECC, OzFlux-TERN, TCOS-Siberia, and USCCC. The ERA-Interim reanalysis data are provided by ECMWF and processed by LSCE. The FLUXNET eddy covariance data processing and harmonization was carried out by the European Fluxes Database Cluster, AmeriFlux Management Project, and Fluxdata project of FLUXNET, with the support of CDIAC and ICOS Ecosystem Thematic Center, and the OzFlux, ChinaFlux and AsiaFlux offices.

Publications
G. Z. Pastorello, D. Papale, H. Chu, C. Trotta, D. A. Agarwal, E. Canfora, D. D. Baldocchi, and M. S. Torn (2017), A new data set to keep a sharper eye on land-air exchanges, Eos, 98 (Published on 17 April 2017). DOI: 10.1029/2017EO071597 (Reference link)

Related Links
http://fluxnet.fluxdata.org/data/fluxnet2015-dataset/

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 13, 2017

Identifying the Important Contributors to Model Variability in a Multiprocess Model

Researchers define a new sensitivity index to quantify the uncertainty contribution from each process under model structural uncertainty.

The Science
Earth system models consist of multiple processes, each of them being a submodel in the integrated system model. A research team, including scientists at Florida State University, Pacific Northwest National Laboratory, and Oak Ridge National Laboratory, derived a new process sensitivity index to rank the importance of each process in a system model with multiple choices of each process model.

The Impact
The new process sensitivity index tackles the model uncertainty in a rigorous mathematical way, which has not been dealt with in conventional sensitivity analyses. Accounting for model structural uncertainty in complex multiphysics, multiprocess models has been a long-recognized need in the modeling community.

Summary
Most of the processes in a multiprocess model could be conceptualized in multiple ways, leading to multiple alternative models of a system. One question often asked is which process contributed to the most variability or uncertainty in the system model outputs. Global sensitivity analysis methods are an important and often used venue for quantifying such contributions and identifying the targets for efficient uncertainty reduction. However, existing methods of global sensitivity analysis only consider variability in the model parameters and are not capable of handling variability that arises from conceptualization of one or more processes. This research developed a new method to isolate the contribution of each process to the overall variability in model outputs by integrating model averaging concepts with a variance-based global sensitivity analysis. The researchers derived a process sensitivity index as a measure of relative process importance, which accounts for variability caused by both process models and their parameters. They demonstrated the new method with a hypothetical groundwater reactive transport modeling case that considers alternative physical heterogeneity and surface recharge submodels. However, the new process sensitivity index is generally applicable to a wide range of problems in hydrologic and biogeochemical problems in Earth system models. This research offers an advanced systematic approach to prioritizing model inspired experiments.

Contacts (BER PM)
David Lesmes
Subsurface Biogeochemical Research Program
David.Lesmes@science.doe.gov (301-903-2977)

Daniel Stover
Terrestrial Ecosystem Science Program
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contacts)
Ming Ye, Florida State University, mye@fsu.edu
Xingyuan Chen, Pacific Northwest National Laboratory (PNNL), Xingyuan.Chen@pnnl.gov
Anthony P. Walker, Oak Ridge National Laboratory (ORNL), walkerap@ornl.gov

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological Research, Early Career Award and PNNL Subsurface Science Research Scientific Focus Area and ORNL Terrestrial Ecosystem Science Scientific Focus Area.

Publication
Dai, H., M. Ye, A. P. Walker, and X. Chen. 2017. “A New Process Sensitivity Index to Identify Important System Processes Under Process Model Uncertainty and Parametric Uncertainty,” Water Resources Research 53(4), 3746-90. [DOI: 10.1002/2016WR019715]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 10, 2017

Linking Microbial Community Composition to Carbon Loss Rates During Wood Decomposition

Fungal community is the dominant decomposer of wood at early stages.

The Science 
During wood decomposition, microbial community composition shifted from fungi-dominated at early stages to relatively more bacteria-dominated ones at later stages. Fungal community dominance during early decomposition stages is associated with relatively high-quality carbon compounds and low wood moisture contents.

The Impact
Our results highlight that fungal groups were strongly influenced by relatively high-quality organic carbon, but bacterial groups are positively correlated with low-quality carbon compounds. This contrasts with the observations of leaf litter decomposition and will provide a key insight toward a better wood decomposition model in DOE’s Earth System Model.

Summary
Although decaying wood plays an important role in global carbon (C) cycling, how changes in microbial community are related to wood C quality and then affect wood organic C loss during wood decomposition remains unclear. In this study, a chronosequence method was used to examine the relationships between wood C loss rates and microbial community compositions during Chinese fir (Cunninghamia lanceolata) stump decomposition. Our results showed that the microbial community shifted from fungi-dominated community at early stages to relatively more bacteria-dominated ones at later stages during wood decomposition. Fungal phospholipid fatty acid content primarily explained wood C loss rates during decomposition. Interestingly, fungi biomass was positively correlated with proportions of relatively high-quality C (e.g., O-alkyl-C), but bacterial biomass was positively correlated with low-quality C. In addition, fungi biomass dominance at the early stages (0-15 years) was associated with low wood moisture (< 20%), while the increase in bacteria biomass at later stages (15-35 years) was associated with increasing wood moisture. Our findings suggest that the fungal community is the dominant decomposer of wood at early stages and may be positively influenced by relatively high-quality wood C and low wood moisture contents. Bacteria were positively influenced by low-quality wood C and high wood moisture contents at later stages. Enhanced understanding of microbial responses to wood quality and environment is important to improve predictions in wood decomposition models.

(PI Contact)
Chonggang Xu 
Los Alamos National Laboratory
cxu@lanl.gov; 505-665-9773

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Funding
This study was funded by the National Natural Science Foundation of China (41371269 and 31570604), the National “973” Program of China (2014CB954002), the China Scholarship Council (201506100166) and the US Department of Energy’s Next Generation Ecosystem Experiment-Tropics.

Publications
Hu Z., Xu C., McDowell N.G., Johnson D.J., Wang M, Huang Z, Zhou X (2017), Linking microbial community composition to C loss during wood decomposition. Soil Biology and Biochemistry, 104: 108-116. doi:10.1016/j.soilbio.2016.10.017. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 07, 2017

Retention of Stored Water Enables Tropical Tree Saplings to Survive Extreme Drought Conditions

The Science  
In order to test the ability of tropical tree saplings to avoid dehydration during severe droughts, as well as the mechanisms and traits associated with dehydration avoidance, potted saplings were subjected to three months without water and their water relations were compared to well-watered control plants.

The Impact
Some tree species remained well hydrated even after three months without water. These species had reduced root surface area in the drought treatment, suggesting a role for root abscission in preventing water loss from roots to soil during severe drought.

Summary
Tree species vary greatly in their ability to extract water from drying soil, yet it is unclear how much they vary in their ability to remain hydrated when soil water is unavailable. To explore variation in the ability to regulate plant water status,  potted saplings of tropical trees were subjected to extreme drought and compared their responses to well-watered plants. After three months, soil in the drought treatment was extremely dry, yet some species had 100% survival and maintained water status similar to well-watered plants (i.e., dehydration-avoiding species). Other species had low survival and reached low water status. The dehydration-avoiding species had traits that favor water storage (e.g., low tissue density), which could provide a reservoir that buffers water status despite water loss, yet they maintained most of their stored water during the drought. The dehydration-avoiding species also had low lateral root area, which was further reduced in the drought treatment. This may slow water loss into dry soil. Together, these results suggest that the ability to avoid dehydration during extreme drought varies greatly among species and is dependent on retaining stored water within the plant.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Brett Wolfe
Smithsonian Tropical Research Institute
btwolfe@gmail.com

Funding
Research was funded with a Garden Club of America award in tropical botany and a Smithsonian Tropical Research Institute short-term fellowship. During manuscript preparation, BT Wolfe was supported in part by the Next Generation Ecosystem Experiments–Tropics, funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research.

Publications
Wolfe, B. T. (2017), Retention of stored water enables tropical tree saplings to survive extreme drought conditions. Tree Physiology, 37 (4): 469-480. doi:10.1093/treephys/tpx001.

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 06, 2017

Global Photosynthesis on the Rise

Plant photosynthesis was stable for hundreds of years before the industrial revolution, but then grew rapidly in the 20th century

The Science  
The researchers discovered the record of global photosynthesis by analyzing Antarctic snow data captured by NOAA. Gases trapped in different layers of Antarctic snow allow scientists to study global atmospheres of the past. These studies focused on a gas stored in the ice that provides a record of the Earth's plant growth.

The Impact
Virtually all life on our planet depends on photosynthesis. The study found that the observation-based carbonyl sulfide (COS) record is most consistent with simulations of climate and the carbon cycle that assume large GPP growth during the twentieth century (31% increase).

Summary
The scientists analyzed a gas called carbonyl sulfide (COS). It’s a cousin of CO2. Plants remove COS from the air through a process that is related to the plant uptake of CO2.  While photosynthesis is closely related to the atmospheric COS level, other processes in oceans, ecosystems, and industry, can change the COS level, as well.  To account for all of these processes, the inter-disciplinary team of scientists developed an Earth system model of COS sources and sinks. Although this COS analysis does not directly constrain models of future GPP growth, it does provide a global-scale benchmark for historical carbon-cycle simulations.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Elliott Campbell, UC Merced
ecmapbell3@ucmerced.edu

Funding
DOE / TES DE-SC0011999

Publication
J.E. Campbell et al., “Large historical growth in global terrestrial gross primary production.” Nature (2017). doi:10.1038/nature22030. (Reference link)

Related Links
Faculty Website: Elliott Campbell

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 03, 2017

A Global Trait-Based Approach to Estimate Leaf Nitrogen Functional Allocations from Observations

Observationally-constrained photosynthetic traits for land models.

The Science
Nitrogen is one of the most important nutrients for plant growth and a major constituent of proteins that regulate photosynthetic and respiratory processes. This study integrated observations from global databases with photosynthesis and respiration models to determine plant-functional-type-specific allocation patterns of leaf nitrogen for photosynthesis and respiration.

The Impact
Our observationally-constrained nitrogen allocation estimates provide insights on mechanisms that operate at a cellular scale within leaves, and can be integrated with ecosystem models to derive emergent properties of ecosystem productivity at local, regional, and global scales.

Summary
We developed here a comprehensive global analysis of nitrogen allocation in leaves for major processes with respect to different plant functional types. Based on our analysis, crops partition the largest fraction of nitrogen to photosynthesis and respiration. Tropical broadleaf evergreen trees partition the least to photosynthesis and respiration. In trees (especially needle-leaved evergreen and tropical broadleaf evergreen trees) a large fraction of nitrogen was not explained by photosynthetic or respiratory functions. Compared to crops and herbaceous plants, this large residual pool is hypothesized to emerge from larger investments in cell wall proteins, lipids, amino acids, nucleic acid, CO2 fixation proteins (other than Rubisco), secondary compounds, and other proteins. The resulting pattern of nitrogen allocation provides insights on mechanisms that operate at a cellular scale within leaves, and can be integrated with ecosystem models to derive emergent properties of ecosystem productivity at local, regional, and global scales.

BER PM Contacts
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

PI Contact
William J. Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov

Funding
This research was supported by the Director, Office of Science, Office of Biological and Environmental Research of the US Department of Energy under Contract No. DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE Arctic) project. The study has been supported by the TRY initiative on plant traits (https://www.try-db.org), which is/has been supported by DIVERSITAS, IGBP, the Global Land Project, the UK Natural Environment Research Council (NERC) through it’s program QUEST (Quantifying and Understanding the Earth System), the French Foundation for Biodiversity Research (FRB), and GIS "Climat, Environnement et Société" France.”

Publications
Ghimire, B., Riley, W. J., Koven, C. D., Kattge, J., Rogers, A., Reich, P. B., and Wright, I.: A global trait-based approach to estimate leaf nitrogen functional allocation from observations, Ecol Appl, DOI:10.1002/eap.1542, 2017. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 03, 2017

Mapping Snow Depth Within a Tundra Ecosystem Using Multiscale Observations and Bayesian Methods

The Science  
We developed a Bayesian approach to integrate a variety of state-of-art snow sensing techniques (e.g., in situ measurements, ground-penetrating radar, phodar on unmanned aerial system (UAS) and airborne lidar) for mapping highly heterogeneous snow depth over ice-wedge polygonal tundra. Our analysis also showed that the end-of-winter snow depth was highly variable in several-meter distances, influenced by microtopography.

The Impact
Snow plays a critical role in Arctic ecosystem functioning, as it influences permafrost thaw, water delivery and carbon exchange. Snow depth is, however, extremely heterogeneous, and traditionally difficult to map in sufficient resolution using conventional point measurements. Although there have been significant technical advances in measuring snow depth (e.g., geophysics and remote sensing), it is still challenging to integrate all these state-of-art data in a harmonized manner due to their different scales and accuracy. The developed Bayesian approach will be an integrating framework for these advanced datasets, allowing us to measure snow depth at high resolution over a large area.

Summary
This paper aim to develop an effective strategy to characterize heterogeneous snow depth over the Arctic tundra, using state-of-art techniques (ground-penetrating radar and UAS phodar) and also to quantify the relationship between snow depth and topography. All the techniques provided fairly accurate estimates of snow depth, while they have different characteristics in term of acquisition time and accuracy. We then investigated the spatial variability of snow depth and its correlation to micro- and macrotopography using the wavelet approach. We found that the end-of-winter snow depth was highly variable over several-meter distances, affected primarily by microtopography. In addition, we developed and implemented a Bayesian approach to integrate multi-scale measurements for estimating snow depth over the landscape.

Contacts (BER PM)
Daniel Stover
Terrestrial Ecosystem Science Program Manager
Daniel.Stover@science.doe.gov

(PI Contact)
Stan D. Wullschleger
Oak Ridge National Laboratory
wullschlegsd@ornl.gov

Funding
This research is supported through contract number DE-AC0205CH11231 to Lawrence Berkeley National Laboratory.

Publications
Wainwright, H. M., Liljedahl, A. K., Dafflon, B., Ulrich, C., Peterson, J. E., Gusmeroli, A., and Hubbard, S. S. “Mapping snow depth within a tundra ecosystem using multiscale observations and Bayesian methods”, The Cryosphere, 11, 857-875, doi:10.5194/tc-11-857-2017, 2017. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 31, 2017

Temperate Forest Methane Sink Diminished by Tree Emissions

Upland forests offset soil methane sinks by 1-6% through stem emissions.

The Science
Upland forest soils remove methane from the atmosphere and are represented in global budgets as net methane sinks. However, we demonstrate that upland trees can also emit methane.

The Impact
Studies of methane fluxes in upland forests have focused on exchanges between the atmosphere and soils, but we conclude that methane fluxes across tree surfaces are also potentially important for upland forest methane budgets.

Summary
Upland forests remove methane from the atmosphere and are represented in global budgets as net methane sinks. However, this view is based almost entirely on measurements of methane exchange across forest soil surfaces, with little attention to the exchange of methane across plant surfaces. Here we report that methane is emitted from the stems of dominant tree species in a temperate upland forest. The source of the methane emitted from these trees is uncertain but may include transport in the transpiration stream from anoxic groundwater, or methane produced inside the tree itself. High-frequency measurements revealed diurnal patterns in the rate of tree-stem methane emissions that support a groundwater source. A simple scaling exercise suggested that tree emissions offset 1-6% of the growing season soil methane sink, and the forest may have briefly changed to a net source of methane to the atmosphere due to tree methane emissions.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Patrick Megonigal
Smithsonian Environmental Research Center
megonigalp@si.edu (443-482-2346)

Funding
This study was supported primarily by the DOE Terrestrial Ecosystem Science program (grant DE-SC0008165). The components of an automated flux system was developed with funds from NSF-ERC MIRTHE (EEC-0540832).

Publications
S.A. Pitz and J.P. Megonigal, “Temperate Forest Methane Sink Diminished by Tree Emissions”. New Phytologist (2017).  [DOI: 10.1111/nph.14559]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 30, 2017

Fine-Root Growth in a Forested Bog is Seasonally Dynamic, but Shallowly Distributed in Nutrient-Poor Peat Environments

Characterizing pre-treatment rooting distribution and dynamics at the site of the SPRUCE experiment.

The Science
As one of the few studies to adapt minirhizotron technology for use in waterlogged peatlands, we were able to provide a rare glimpse into the hidden patterns of root distribution and dynamics in a forested, ombrotrophic bog.

The Impact
Fine roots contribute to ecosystem biogeochemical cycles through resource acquisition and respiration, as well as their death and decay, but are understudied in peatlands. Changes in the distribution of roots throughout the peat profile, across the landscape, and over time could alter the delicate balance of peat accumulation.

Summary
In this fundamental study, we aimed to determine how the amount and timing of fine-root growth in a forested, ombrotrophic bog varied across gradients of vegetation density, peat microtopography, and changes in environmental conditions across the growing season and throughout the peat profile. We quantified fine-root peak standing crop and growth using non-destructive minirhizotron technology over a two-year period, focusing on the dominant woody species in the bog. We found that fine-root standing crop and growth varied spatially across the bog in relation to tree density and microtopography, and we observed tradeoffs in root growth in relation to aboveground woody growth rather than environmental variables such as peat temperature and light. A shallow water table level constrained living fine roots to the aerobic zone, which is extremely poor in plant-available nutrients, and ancient, undecomposed, fine roots in peat below the water table suggest a significant contribution of roots to historical accumulated peat. We expect the controls over the distribution and dynamics of fine roots in this bog to be sensitive to projected warming and drying in northern peatlands.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Colleen M. Iversen
Senior Staff Scientist
Environmental Sciences Division and
Climate Change Science Institute
Oak Ridge National Laboratory
iversencm@ornl.gov
(865) 214-3961

Funding
Department of Energy, Office of Science, Biological and Environmental Research Program.  

Publications
Iversen, C.M., J. Childs, R.J. Norby, T.A. Ontl, R.K. Kolka, D.J. Brice, K.J. McFarlane, and P.J. Hanson. 2017. Fine-root growth in a forested bog is seasonally dynamic, but shallowly distributed in nutrient-poor peat. Plant and Soil, DOI: 10.1007/s11104-017-3231-z. (Reference link)

Related Links
Data products:
Iversen, C.M., J. Childs, R.J. Norby, A. Garrett, A. Martin, J. Spence, T.A. Ontl, A. Burnham, and J. Latimer. 2017. SPRUCE S1 bog fine-root production and standing crop assessed with minirhizotrons in the Southern and Northern ends of the S1 bog. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A. http://dx.doi.org/10.3334/CDIAC/spruce.019.

Iversen, C.M., A. Garrett, A. Martin, M.R. Turetsky, R.J. Norby, J. Childs, and T.A. Ontl. 2017. SPRUCE S1 bog tree basal area and understory community composition assessed in the Southern and Northern ends of the S1 bog. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A. http://dx.doi.org/10.3334/CDIAC/spruce.024.

Iversen, C.M., T.A. Ontl, D.J. Brice, and J. Childs. 2017. SPRUCE S1 Bog plant-available nutrients assessed with ion-exchange resins from 2011-2012 in the Southern end of the S1 bog. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A. http://dx.doi.org/10.3334/CDIAC/spruce.022.

Iversen, C.M., J. Latimer, A. Burnham, D.J. Brice, J. Childs, and H.M. Vander Stel. 2017. SPRUCE plant-available nutrients assessed with ion-exchange resins in experimental plots, beginning in 2013. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A. http://dx.doi.org/10.3334/CDIAC/spruce.036.

Ontl, T.A., and C.M. Iversen. 2017. SPRUCE S1 bog areal coverage of hummock and hollow microtopography assessed along three transects in the S1 bog. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A. http://dx.doi.org/10.3334/CDIAC/spruce.023.

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 13, 2017

Building a Better Foundation: Improving Root-Trait Measurements to Understand and Model Plant and Ecosystem Processes

Priorities for capturing root trait variation in model frameworks

The Science
Fine roots play important roles in acquiring soil nutrients and water for plant growth. However, it has been difficult to determine how traits of fine roots change across environments and how these changes impact plant and ecosystem processes.

The Impact
We highlight barriers limiting our knowledge of how fine roots work in ecosystems, and importantly, we suggest tractable ways in which we might overcome those barriers. Refocusing our efforts to measure multiple aspects of roots traits and function in ways that can be rigorously compared across species will rapidly improve understanding of terrestrial ecosystems.

Summary
Trait-based approaches provide a useful framework to investigate plant strategies for resource acquisition, growth, and competition, as well as plant impacts on ecosystem processes. Despite significant progress capturing trait variation within and among stems and leaves, identification of trait syndromes within fine-root systems and between fine roots and other plant organs is limited. Here we discuss three underappreciated areas where focused measurements of fine-root traits can make significant contributions to ecosystem science. These include assessment of spatiotemporal variation in fine-root traits, integration of mycorrhizal fungi into fine-root-trait frameworks, and the need for improved scaling of traits measured on individual roots to ecosystem-level processes. Progress in each of these areas is providing opportunities to revisit how below-ground processes are represented in terrestrial biosphere models. Targeted measurements of fine-root traits with clear linkages to ecosystem processes and plant responses to environmental change are strongly needed to reduce empirical and model uncertainties. Further identifying how and when suites of root and whole-plant traits are coordinated or decoupled will ultimately provide a powerful tool for modeling plant form and function at local and global scales.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
M. Luke McCormack
Department of Plant and Microbial Biology, University of Minnesota
mltmcc@gmail.com

Funding
The authors acknowledge support from the US Department of Energy (DOE) Terrestrial Ecosystem Sciences (TES) Program, the New Phytologist Trust, and the Chinese Academy of Sciences (CAS) for supporting the workshop where the initial ideas for this manuscript were developed.

Publications
McCormack, M. L. et al. Building a better foundation: improving root-trait measurements to understand and model plant and ecosystem processes. New Phytologist, doi:10.1111/nph.14459 (2017). (Reference link)

Related Links
www.mlmccormack.com

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 09, 2017

Soils Could Release Much More Carbon Than Expected as Climate Warms

Findings from a whole-soil warming experiment show that deeper soil layers are more sensitive to warming than previously thought.

The Science 
Scientists created a field experiment in a conifer forest in California to explore, for the first time, what happens to organic carbon trapped in soil when all soils are warmed. In this case, the soil layers extended to a depth of 100 cm. Warming the whole profile by 4°C increased annual soil respiration by 34% to 37%. More than 40% of this increase in respiration came from below 15-cm depth (i.e., below the depth considered by most studies). 

The Impact
The impact of warming on soil carbon dioxide (CO2) flux is a major uncertainty in climate feedbacks. This whole-soil warming experiment found a larger respiration response than (1) many other controlled experiments, which may have missed the response of deeper soils; and (2) most models. Thus, the strength of the soil carbon-climate feedback may be underestimated.

Summary
Soil organic carbon harbors three times as much carbon as Earth’s atmosphere, more than half of that below 20-cm depth. The response of whole-soil profiles to warming has not been tested in situ. In this deep warming experiment in mineral soil, CO2 production from all soil depths increased significantly with 4°C warming; annual soil respiration increased by 34% to 37%. All depths responded to warming with similar temperature sensitivities, driven by decomposition of decadal-aged carbon. Whole-soil warming reveals a larger soil respiration response than many in situ experiments, most of which only warm the surface soil, and models.  

In this year-round experiment, plots were warmed by a ring of 22 vertical heating cables installed to 2.4-m depth. Three plots (3-m diameter each) were warmed, and three served as controls. Soil respiration was measured by chambers at the surface and gas tubes at five depths. Radiocarbon content of CO2 and soil fractions suggests that respiration—and its warming response—was dominated by decadal cycling carbon.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov; 301-903-0289

PI Contact
Margaret S. Torn
Lawrence Berkeley National Laboratory
mstorn@lbl.gov

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program under contract number DE-AC02-05CH11231.

Publication
C. E. Hicks Pries, C. Castanha, R. C. Porras, and M. S. Torn, “The whole-soil carbon flux in response to warming.” Science  (2017). [DOI: 10.1126/science.aal1319] (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



One of the experimental heating plots at Blodgett Forest Research Station in California. The ring around the plot protects the wiring supplying 22 heating cables that each go 2.4 meters into the ground. Each plot also has soil temperature and moisture sensors that measure continuously and automated chambers that measure soil respiration every 30 minutes. [Image courtesy Lawrence Berkeley National Laboratory]



March 06, 2017

Can Models Predict Grassland Responses to Environment?

Challenging terrestrial biosphere models with data from the long-term multi-factor prairie heating and CO2 enrichment experiment.

The Science
Researchers challenged ten carbon-cycle models, often used to simulate ecosystem responses to environmental change, to simulate a grassland in Wyoming subjected to experimental CO2 enrichment and increased temperature. 

The Impact
Carbon-cycle models used for regional or global simulations are known to perform poorly when used to simulate a specific site. Researchers identified a number of areas for carbon-cycle model improvement. Model development to improve the accuracy of grassland simulations should focus on improving the realism of the controls of water availability on growth and soil nitrogen in these non-forested ecosystems.

Summary
Multi-factor experiments are often advocated as important for advancing terrestrial biosphere models, but this claim is rarely tested. As part of the DOE supported Free Air CO2 Enrichment Model Data Synthesis (FACE-MDS) project, researchers aimed to investigate how a CO2 enrichment and warming experiment can be used to identify a road map for carbon-cycle model improvement. Researchers found that the ten models tested simulated a wide spread in annual above-ground growth in current environmental conditions (i.e., not experimentally manipulated conditions). Comparison with data highlighted that the reasons for these model shortcomings were poor representation of: carbon allocation, seasonality of growth, the impact of water stress on the seasonality of growth, sensitivity to water stress, and soil nitrogen availability. In response to the experimentally manipulated conditions, models generally over-estimated the effect of warming on leaf onset and were lacking the mechanism to allow CO2-induced water savings to extend the growing season. However, when both CO2 and warming were increased, the observed effects of the experimental increase in CO2 and temperature on plant growth were subtle and contingent on water stress, phenology, and species composition. Since the models did not correctly represent these processes under ambient and single-factor conditions, little extra information was gained by comparing model predictions against interactive responses. The study outlines a series of key areas in which this and future experiments could be used to improve model predictions of grassland responses to global change.

Contacts
(BER PM)

Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289) 

(PI Contact)
Anthony Walker
Oak Ridge National Laboratory
walkerap@ornl.gov

Funding
DOE Office of Science BER, FACE Model Data Synthesis project

Publications
De Kauwe, M. G. et al. Challenging terrestrial biosphere models with data from the long-term multifactor Prairie Heating and CO2 Enrichment experiment. Global Change Biology, awaiting page numbers (2017). [doi:10.1111/gcb.13643] (Reference link)

Related Links
FACE-MDS
UDSA PHACE experiment

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 28, 2017

A New Fine-Root Database Addresses Belowground Challenges in Plant Ecology

The global Fine-Root Ecology Database will improve understanding of belowground plant ecology and its effects on ecosystem functioning.

The Science  
Researchers have organized tens of thousands of data points describing the functional characteristics of small-diameter “fine” plant roots across environmental gradients into a single common framework, the Fine-Root Ecology Database (FRED). These data, which are freely available to the public (see http://roots.ornl.gov), will improve understanding and model representation of belowground processes.

The Impact
Fine roots play an important role in ecosystem carbon, water, and nutrient cycling. However, fine-root traits are underrepresented in global trait databases, hindering efforts to link belowground plant function with changing environmental conditions and contributing to the coarse representation of fine roots in terrestrial biosphere models. FRED represents a critical step toward improving understanding of belowground plant ecology and its effects on ecosystem functioning.

Summary
Variation and tradeoffs within and among plant traits are increasingly being harnessed by empiricists and modelers to understand and predict ecosystem processes under changing environmental conditions. While fine roots play an important role in ecosystem functioning, fine-root traits are underrepresented in global trait databases. This deficiency has hindered efforts to analyze fine-root trait variation and link it with plant function and environmental conditions at a global scale. The new database called FRED, which so far includes more than 70,000 observations encompassing a broad range of root traits and also includes associated environmental data, represents a critical step toward improving understanding of belowground plant ecology. For example, FRED facilitates the quantification of variation in fine-root traits across root orders, species, biomes, and environmental gradients, while also providing a platform for assessments of covariation among root, leaf, and wood traits, the role of fine roots in ecosystem functioning, and the representation of fine roots in terrestrial biosphere models. Continued input of observations into FRED to fill gaps in trait coverage will improve understanding of changes in fine-root traits across space and time.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301) 903-0289

(PI Contact)
Colleen M. Iversen
Senior Staff Scientist
Environmental Sciences Division and
Climate Change Science Institute
Oak Ridge National Laboratory
iversencm@ornl.gov
(865) 214-3961

Funding
This work was supported in part by the U. S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program.

Publications
Iversen, C. M., M. L. McCormack, A. S. Powell, C. B. Blackwood, et al. 2017. “Viewpoint: A Global Fine-Root Ecology Database to Address Belowground Challenges in Plant Ecology,” New Phytologist, DOI: 10.1111/nph.14486. (Reference link)

Iversen, C. M., A. S. Powell, M. L. McCormack, C. B. Blackwood. et al. 2016.“Fine-Root Ecology Database (FRED): A Global Collection of Root Trait Data with Coincident Site, Vegetation, Edaphic, and Climatic Data, Version 1.” Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee, U.S.A. Access on-line at: http://dx.doi.org/10.3334/CDIAC/ornlsfa.005.

Related Links
FRED website
ORNL research highlight

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Map of Distinct Locations Associated with Observations in the Fine-Root Ecology Database (FRED). Shown are the locations of studies collecting root trait observations for plants growing outdoors, not in pots (closed blue circles, 979 distinct locations), and the locations of studies collecting root trait observations from plants growing in pots, outdoors or indoors, or from plants growing indoors in hydroponic systems or mesocosms (open blue circles, 54 distinct locations). Only about 60% of the root samples in FRED were associated with georeferenced locations; some locations were estimated from the study’s specified location for the purposes of this figure. [Image courtesy Iversen et al. 2017. “Viewpoint: A Global Fine-Root Ecology Database to Address Belowground Challenges in Plant Ecology,” New Phytologist, DOI: 10.111.nph.14486]



February 24, 2017

An Ecosystem-Scale, Experimental System to Study Whole-Ecosystem Warming

Scientists have developed protocols for continuous warming and elevated CO2 experimental manipulations of tall-stature peatland forests.

The Science
Scientists at Oak Ridge National Laboratory have documented an experimental system that combines aboveground and deep-soil heating approaches to provide researchers with a plausible method with which to glimpse future environmental conditions for intact peatland ecosystems.

The Impact
This experimental system enables researchers to study a broad range of organisms (e.g., microbes, moss, shrubs, trees, and insects) and ecosystem processes (e.g., carbon cycle and water use) under realistic field environments for a broad range of alternative environments that may occur in the future.

Summary
This study describes methods to achieve and measure both deep-soil heating (0 m to 3 m) and whole-ecosystem warming (WEW) appropriate to the scale of tall-stature, boreal forest peatlands. The methods were developed to provide scientists with a plausible set of ecosystem-warming scenarios within which immediate and longer-term (1 decade) responses of organisms (microbes to trees) and ecosystem functions (carbon, water, and nutrient cycles) could be measured. Elevated carbon dioxide also was incorporated to test for interactions with temperature. The WEW approach was successful in sustaining a wide range of aboveground and belowground temperature treatments (as much as +9 °C) in large 115-m2, open-topped enclosures. The system is functional year round, including warm summer and cold winter periods. The study contrasts the WEW method with prior closely related field-warming approaches and includes a full discussion of factors that must be considered in interpreting experimental results. The WEW method enables observations of future temperature conditions not available in the current observational record, thereby providing a plausible glimpse of future environmental conditions.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov

(PI Contact)
Paul J. Hanson
hansonpj@ornl.gov

Funding
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, and Graduate Fellowship Program (DE-AC05-06OR23100 to A. L. G.).

Publication
Hanson, P. J., J. S. Riggs, W. R. Nettles, J. R. Phillips, M. B. Krassovski, L. A. Hook, A. D. Richardson, D. M. Aubrecht, D. M. Ricciuto, J. M. Warren, and C. Barbier. 2017. “Attaining Whole-Ecosystem Warming Using Air and Deep Soil Heating Methods with an Elevated CO2 Atmosphere,” Biogeosciences 14, 861-83. DOI: 10.5194/bg-14-861-2017. (Reference link)

Related Links
http://mnspruce.ornl.gov

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Diagram of the SPRUCE open-top enclosure for air warming (A) and the infrastructure for deep peat heating (B). [Image courtesy Hanson et al. 2017. “Attaining Whole-Ecosystem Warming Using Air and Deep Soil Heating Methods with an Elevated CO2 Atmosphere,” Biogeosciences 14, 861-83. DOI: 10.5194/bg-14-861-2017]



Aerial view of the SPRUCE experimental site showing 10 open-top enclosures. [Image courtesy Hanson et al. 2017. “Attaining Whole-Ecosystem Warming Using Air and Deep Soil Heating Methods with an Elevated CO2 Atmosphere,” Biogeosciences 14, 861-83. DOI: 10.5194/bg-14-861-2017]



February 23, 2017

Microbes Drive Methane Release from Wetlands

Study reveals how shallow wetlands act as hotspots for greenhouse gas generation.

The Science
Inland waters and wetlands are increasingly recognized as critical sites of methane emissions to the atmosphere, but little is known about the biological and geochemical processes driving the release of this powerful greenhouse gas from these ecosystems. A new study of microbial and geochemical processes in shallow wetlands known as “potholes” reveals that these wetlands are biogeochemical hot spots for some of the highest methane fluxes to the atmosphere ever reported.

The Impact
The study's findings reveal high concentrations of carbon and sulfur compounds in the Prairie Pothole Region wetlands of North America and that these wetlands support microorganisms that generate high levels of methane. Moreover, the results show that this region is a hot spot of geochemical and microbial activity and plays an important role in regional elemental cycling—the flow of chemical elements and compounds between living organisms and the physical environment.

Summary
Small ponds and lakes recently have been found to play an oversized role in degrading carbon and catalyzing fluxes of greenhouse gases such as methane and carbon dioxide to the atmosphere. The Prairie Pothole Region is a huge wetland ecosystem containing thousands of shallow wetlands that span five states in the United States and two provinces in Canada. This region's wetland sediments contain some of the highest concentrations of dissolved organic carbon and sulfur compounds ever recorded in terrestrial aquatic environments. The observations suggest that these wetlands likely support high levels of microbial activity, which, in turn, could account for substantial greenhouse gas emissions from this ecosystem. To explore this possibility, researchers from The Ohio State University; Environmental Molecular Sciences Laboratory (EMSL), a Department of Energy Office of Science user facility; and the U.S. Geological Survey conducted one of the first studies of coupled geochemical and microbial processes driving methane emissions from Prairie Pothole Region wetlands. They collected sediment and pore water samples from these wetlands; used chemical analysis techniques to measure the concentrations of carbon, sulfur and methane; and conducted gene sequencing to identify members of the microbial community. They also performed in-depth chemical analysis of the dissolved carbon pools using 600-MHz nuclear magnetic resonance (NMR) spectrometers and the 12 Tesla Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer at EMSL. The findings suggest that conversion of abundant carbon pools into methane in the Prairie Pothole Region results in some of the highest fluxes of this greenhouse gas to the atmosphere ever reported. Moreover, high levels of carbon and sulfur compounds support some of the highest sulfate reduction rates ever measured in terrestrial aquatic environments. Taken together, the findings reveal a significant and previously underappreciated role for this ecosystem in supporting extremely high levels of microbial activity that directly impact terrestrial elemental cycling. As such, the results offer novel insights into how Prairie Pothole Region wetlands and other small inland waters act as hot spots for greenhouse gas generation.

BER PM Contact
Paul Bayer, SC-23.1, 301-903-5324

PI Contact
Michael J. Wilkins
Ohio State University
wilkins.231@osu.edu

EMSL Contacts
Malak Tfaily
malak.tfaily@pnnl.gov
David Hoyt
david.hoyt@pnnl.gov

Funding
This work was supported by the U.S. Department of Energy’s Office of Science (Office of Biological and Environmental Research), including support of the Environmental Molecular Sciences Laboratory (EMSL) and the DOE Joint Genome Institute, both DOE Office of Science User Facilities; U.S. Geological Survey Climate and Land Use Change R&D Program; and National Science Foundation.

Publication
P. Dalcin Martins, D.W. Hoyt, S. Bansal, C.T. Mills, M. Tfaily, B.A. Tangen, R.G. Finocchiaro, M.D. Johnston, B.C. McAdams, M.J. Solensky, G.J. Smith, Y-P Chin, and M.J. Wilkins, “Abundant carbon substrates drive extremely high sulfate reduction rates and methane fluxes in Prairie Pothole Wetlands.” Global Change Biology (2017). [DOI: 10.1111/gcb.13633] (Reference link)

Related Links
EMSL Science Highlight: Microbes Drive Methane Release from Wetlands

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 21, 2017

Observational Needs for Estimating Alaskan Soil Carbon Stocks Under Current and Future Climate

A geospatial analysis optimized the distribution of observation locations needed for reducing uncertainties in soil carbon stock estimates.

The Science 
Researchers used a geospatial approach that integrates existing observations with the multivariate spatial heterogeneity of soil-forming factors. The approach was developed to identify the optimal number and spatial distribution of observation sites needed to improve estimates of soil organic carbon stocks under current and projected future climatic conditions.

The Impact
The magnitude, vulnerability, and spatial distribution of soil carbon stocks are major sources of uncertainty in projected carbon-climate feedbacks attributed to the permafrost region. Study results provide a spatially optimized set of locations designed to guide new field observations for constraining the uncertainties in soil carbon estimates and providing robust spatial benchmarks for Earth system model results.

Summary
Representing land surface spatial heterogeneity is a scientific challenge that is critical for designing observation schemes to reliably estimate soil properties. Researchers led by Argonne National Laboratory developed a geospatial approach to identify an optimum distribution of observation sites for improving the characterization of soil organic carbon stocks across Alaska. By using environmental data expected to influence soil formation as proxies for representing the spatial distribution of soil organic carbon stocks, the scientists determined that complementing data from existing samples with 484 new observation sites would be needed to characterize average whole-profile soil organic carbon stocks across Alaska at a confidence interval of 5 kg C m-2. Estimates to depths of 0 m to 1 m and 0 m to 2 m with the same level of confidence would require 309 and 446 new observation sites, respectively. New observation needs are greater for scrub (mostly tundra) than forest land cover types, and ecoregions in southwestern Alaska are among the most under-sampled. The number and locations of required observations are not greatly altered by changes in climatic variables through 2100 as projected by Intergovernmental Panel on Climate Change emission scenarios. Study results serve as a guide for future sampling efforts to reduce existing uncertainty in soil organic carbon observations and improve benchmarks for Earth system model results.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Julie D. Jastrow
Argonne National Laboratory
jdjastrow@anl.gov (630-252-3226)

(Corresponding Author Contact)
Umakant Mishra
Argonne National Laboratory
umishra@anl.gov (630-252-1108)

Funding
This study was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Sciences Division, Terrestrial Ecosystem Science program under contract DE-AC02-06CH11357 to Argonne National Laboratory.

Publication
U. W. A. Vitharana, U. Mishra, J. D. Jastrow, R. Matamala, and Z. Fan, “Observational needs for estimating Alaskan soil carbon stocks under current and future climate.” Journal of Geophysical Research: Biogeosciences (2017). [DOI:10.1002/2016JG003421] (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Distribution of optimized sample locations for characterizing whole-profile soil organic carbon stocks across Alaska under present climate at a confidence interval of 5 kg C m-2. Green triangles show the locations where new observations are needed and red dots show recommended sites represented by existing observations. [Image reprinted under a Creative Commons Attribution License (CC BY) from Vitharana, U.W.A., et al. 2017. “Observational Needs for Estimating Alaskan Soil Carbon Stocks Under Current and Future Climate,” Journal of Geophysical Research: Biogeosciences, DOI: 10.1002/2016JG003421. Copyright 2017 Vitharana, Mishra, Jastrow, Matamala, and Fan]



February 07, 2017

Shifts in Biomass and Productivity for a Subtropical Dry Forest in Response to Simulated Elevated Hurricane Disturbances

Hurricane effects on dry tropical forests.

The Science
Caribbean tropical forests are subject to hurricane disturbances of great variability. In addition to natural storm incongruity, climate change can alter storm formation, duration, frequency, and intensity. This model-based investigation assessed the impacts of multiple storms of different intensities and occurrence frequencies on the long-term dynamics of subtropical dry forests in Puerto Rico. This is the first attempt to model hurricane effects for dry forests of Puerto Rico; a unique, overlooked, and threatened biome of the world.

The Impact
Our results revealed that more frequent storms led to a switch in simulated carbon accumulation from negative (i.e., source) to positive (i.e., sink), with coarse woody debris and leaf production being major carbon components that should be included in disturbance modeling. While there is evidence that hurricane intensity has been increasing in the Atlantic Basin over the past 30 years, we predict the long-term forest structure and productivity will not be largely affected in relationship to storm intensity alone. Additionally, our results suggest that subtropical dry forests will remain resilient to hurricane disturbances.

Summary
For this study we used a previously validated individual-based dynamic vegetation gap model, and developed a new hurricane damage routine parameterized with site- and species-specific hurricane effects. Increasing the frequency of hurricanes decreased aboveground biomass by between 5% and 39%, and increased NPP between 32% and 50%. In contrast, increasing hurricane intensity did not create a large shift in the long-term average forest structure, net primary productivity (NPP), or annual carbon accumulation (ACA) from that of historical hurricane regimes, but produced large fluctuations in biomass. With an increase in the frequency of storms, the total ACA switched to positive due to shifts in leaf production, annual litterfall, and coarse woody debris inputs, indicating a carbon sink into the forest over the long-term and major carbon components that should be included in disturbance modeling. Our results suggest that subtropical dry forests will remain resilient to hurricane disturbance. However carbon stocks will decrease if future climates increase hurricane frequency by 50% or more. These results, and the new disturbance damage routine, are being considered for DOE's new dynamic vegetation model FATES, which is being integrated into ALMv1 and used by the NGEE-Tropics Project.

Contacts
(BER PM)

Dan Stover and Dorothy Koch
Daniel.Stover@science.doe.gov  (301-903-0289) and Dorothy.Koch@science.doe.gov (301-903-0105)

(PI Contact)
Jeffrey Q. Chambers
Lawrence Berkeley National Lab
jchambers@lbl.gov

William J. Riley
Lawrence Berkeley National Lab
wjriley@lbl.gov

Funding
DE-AC02-05CH11231 as part of their Next Generation Ecosystem Experiment-Tropics (NGEE-Tropics) and Accelerated Climate Modeling for Energy (ACME) programs.

Publication
Holm, J.A., S.J. Van Bloem, G.R. Larocque, and H.H. Shugart. Shifts in biomass and productivity for a subtropical dry forest in response to simulated elevated hurricane disturbances. Environ. Res. Lett. 12; 025007 (2017).  DOI: 10.1088/1748-9326/aa583c (Reference link)
Special Issue: "Focus on Tropical Dry Forest Ecosystems and Ecosystem Services in the Face of Global Change"

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 04, 2017

Windthrow Variability in Central Amazonia

A new study pinpoints the seasonal and interannual variability of windthrows.

The Science
Windthrows (gaps of uprooted or broken trees) are a recurrent disturbance in Amazonia that affects the persistence of woody biomass, which, in turn, affects patterns of productivity and biomass, floristic composition, and soil composition in the basin. Windthrows are produced by severe convective events that are expected to become more frequent with climate change. Yet the variability of windthrows over time has not been investigated. Studying the frequency of their occurrence is key to understanding the atmospheric conditions that produce these events.

The Impact
The study’s findings show that windthrows occurred every year and were more frequent from September through February. One driver of windthrows are southerly squall lines (that form in southern Amazonia and move to northeast Amazonia). These squall lines were found to be more frequent than their previously reported ~50-year interval. These results will improve representations of tree mortality in Earth system models and, in particular, the Accelerated Climate Modeling for Energy (ACME) Land Model (ALM).

Summary
Windthrows are a recurrent disturbance in Amazonia and are an important driver of forest dynamics and carbon storage. In this study, researchers present, for the first time, the seasonal and interannual variability of windthrows, focusing on central Amazonia, and discuss the potential meteorological factors associated with this variability. Landsat images from 1998 through 2010 were used to detect the occurrence of windthrows, which were identified based on their spectral characteristics and shape. They were found to occur every year, but were more frequent between September and February. Organized convective activity associated with multicell storms embedded in mesoscale convective systems—such as northerly squall lines (that move from northeast to southwest), and southerly squall lines (that move from southwest to northeast)—can cause windthrows. The researchers also found that southerly squall lines occurred more frequently than their previously reported ~50-year interval. At the interannual scale, the study did not find an association between El Niño-Southern Oscillation and windthrows.

Contacts (BER PM)
Renu Joseph and Dan Stover
Renu.Joseph@science.doe.gov (301-903-9237), and Daniel.Stover@science.doe.gov (301-903-0289) 

PI Contact
William J. Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov 

Funding
This research was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under contract DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments-Tropics project and Regional and Global Climate Modeling program. 

Publication
R. I. Negron-Juarez, H. S. Jenkins, C. F. M. Raupp, W. J. Riley, L. M. Kueppers, D. Magnabosco Marra, G. H. P. Ribeiro, M. T. Monterio, L. A. Candido, J. Q. Chambers, and N. Higuch, “Windthrow Variability in Central Amazonia.” Atmosphere 8(2), 28 (2017). DOI:10.3390/atmos8020028. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Annual occurrence of windthrow events (solid and dashed lines) in central Amazonia over hydrological years 1998–1999 to 2009–2010, plotted against annual rainfall (gray bars). La Niña years highlighted in blue; El Niño years highlighted in red. [Image courtesy Negron-Juarez et al., 2017. DOI: 10.3390/atmos8020028. (CC BY 4.0)]



January 27, 2017

Monoterpene ‘Thermometer’ of Tropical Forest-Atmosphere Response of High Temperature Stress

Discovery of a Tropical Forest Biochemical “Thermometer”

The Science  
Tropical forests absorb large amounts of atmospheric CO2 through photosynthesis but elevated temperatures suppress this absorption while promoting biochemical emissions of monoterpenes. Plant monoterpenes are hypothesized to be involved in thermotolerance of photosynthesis, but observations are scarce and global models assume that tropical monoterpene emissions are dominated by α-pinene. Moreover, models assume that composition of monoterpene emissions is insensitive to temperature. Using 13CO2 labeling, we show that monoterpene emissions from tropical leaves derive from recent photosynthesis and demonstrate distinct temperature optima for five groups, potentially corresponding to different enzymatic temperature-dependent reaction mechanisms within β-ocimene synthases. As diurnal and seasonal leaf temperatures increased during the Amazonian 2015 El Niño event, leaf and landscape monoterpene emissions showed strong linear enrichments of the highly reactive β-ocimenes (Group 1) at the expense of other monoterpene isomers (Groups 4-5). This high positive sensitivity of Group 1 monoterpenes and negative temperature sensitivity of α-pinene (Group 2), typically assumed to be the dominant monoterpene with moderate reactivity, was not accurately simulated by current global emission models.

The Impact
Given that β-ocimenes are highly reactive with respect to both atmospheric and biological oxidants, the results suggest that highly reactive β-ocimenes may play important roles in the thermotolerance of photosynthesis by functioning as effective antioxidants within plants and as efficient atmospheric precursors of secondary organic aerosols. Thus, monoterpene composition may represent a new sensitive ‘thermometer’ of leaf oxidative stress and atmospheric reactivity, and therefore a new tool in future studies of warming impacts on tropical biosphere-atmosphere carbon-cycle feedbacks. Plant response to warming may involve a single enzyme/gene (ocimene synthase); insertion into transgenic plants will facilitate quantitative studies on the role of light-dependent monoterpences in oxidative stress responses including thermotolerance of photosynthesis. This presents opportunities for the development of the ‘monoterpene thermometer’ gene in agricultural plants as a sensor of plant oxidative stress during environmental extremes.

Summary
Tropical forests are increasingly threatened by increased temperatures which can lead to oxidative stress, but the physiological mechanisms plants use to cope with these conditions remain poorly understood. In this study, we report the discovery of a tropical forest, “monoterpene thermometer” where the composition of monoterpene emissions changes as a function of temperature. We found a high temperature sensitivity of the composition of tropical leaf monoterpene emissions across a wide range of temporal (minutes to seasons) and spatial (leaf to ecosystem) scales. As monoterpene emissions increased with temperature, the composition shifted such that highly reactive monoterpenes accounted for a larger fraction of the total under high temperature stress. This result suggests a biological function of these highly reactive monoterpenes in the tropics. Given their high reactivity to both atmospheric and biological oxidants, the results suggest that they play important roles in the thermotolerance of photosynthesis by functioning as effective antioxidants within plants and as efficient atmospheric precursors of secondary organic aerosols, thereby enhancing surface cooling and water recycling. Thus, monoterpene composition may represent a new sensitive ‘thermometer’ of leaf oxidative stress and atmospheric reactivity, and therefore a new tool in future studies of warming impacts on tropical biosphere-atmosphere carbon-cycle feedbacks.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Kolby Jardine
Lawrence Berkeley National Laboratory
Climate and Ecosystem Sciences Division
kjjardine@lbl.gov 

Funding
This work was supported as part of the GoAmazon 2014/5 and the Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics) funded by the U.S.Department of Energy, Office of Science, Office of Biological and Environmental Research through contract No. DE-AC02-05CH11231 to LBNL, as part of DOE’s Terrestrial Ecosystem Science Program. Additional funding for this research was provided by the Brazilian Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). 

Publications
Jardine, K. J., Jardine, A. B., Holm, J. A., Lombardozzi, D. L., Negron-Juarez, R. I., Martin, S. T., Beller, H. R., Gimenez, B. O., Higuchi, N., and Chambers, J. Q. (2017) Monoterpene ‘thermometer’ of tropical forest-atmosphere response to climate warming. Plant, Cell & Environment, 40: 441-452. doi: 10.1111/pce.12879. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 25, 2017

Climate Warming Could Cause Mountaintop Plants and Soils to Become Out of Sync

Plants and soil microorganisms may be altered by climate warming at different rates and in different ways, meaning important nutrient patterns could be misaligned.

The Science   
Warmer climates on mountaintops will alter the activity of plants and soil microbes, which can alter the availability and movement of important nutrients such as nitrogen, phosphorous, and carbon. As a result, these cycles may become out of step with their historic patterns at high elevations, severely impacting plants that have evolved under those patterns.

The Impact
In many mountain ecosystems around the world, nitrogen and phosphorus cycles at warmer, low elevations are becoming decoupled, while they are constrained at higher, cool elevations. Consequently, plants may not be able to “march up the mountainside” when it warms, as many models predict. A recent study shows how mountain ecosystems, which are biodiversity hotspots and provide numerous important human services such as clean drinking water, may respond to warming in the future.

Summary
Despite interest in how climate warming affects ecological processes, remarkably little is known about whether similar types of ecosystems respond to warming in different locations. By comparing seven replicated temperate treeline ecotones worldwide, researchers showed that comparable changes to temperature affect plant community-level nutrient dynamics in remarkably similar ways across contrasting regions. Notably, their study reveals that despite broad differences in regional floras and geologies, declining temperatures at high elevations universally constrained plant nutrient dynamics. This finding has broad global change implications, given the high risk that alpine environments face under global climate change.

BER PM Contact
Daniel Stover, SC-23.1, Daniel.Stover@science.doe.gov, 301-903-0289

PI Contact
Aimee T. Classen      
University of Vermont
Aimee.Classen@uvm.edu

Funding
This work was made possible by a Wallenberg Scholars Award to D.A.W.; regional support from Fondecyt 1120171 to A.F.; National Science Foundation Dimensions of Biodiversity grant (NSF-1136703), Carlsberg Fund grant, and support from the Danish National Research Foundation to the Center for Macroecology, Evolution, and Climate to N.J.S.; U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program award (DE-SC0010562) to A.T.C.; support from the UK Natural Environment Research Council to R.D.B.; support from the BiodivERsA project REGARDS (ANR-12-EBID-004-01) to J.-C.C., S.L., and K.G. and REGARDS (FWF-I-1056) to M.B.; support from the Netherlands Organization for Scientific Research (VENI 451-14-017) to D.L.O.; and support from the Natural Sciences and Engineering Research Council of Canada to Z.G.

Publication
J. Mayor et al., “Elevation alters ecosystem properties across temperate treelines globally.” Nature 542, 91-95 (2017). DOI:10.1038/nature21027. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Treeline along an elevational gradient in the Colorado Rockies, one of seven mountaintop regions sampled in a recent study. [Image courtesy Aimee Classen, University of Vermont]



January 17, 2017

PeRL: A Circum-Arctic Permafrost Region Pond and Lake Database

The Science  
CE1Ponds and lakes are abundant in Arctic permafrost lowlands and play important roles in Arctic wetland ecosystems by regulating carbon, water, and energy fluxes and providing freshwater habitats. However, waterbodies with surface areas smaller than 104 m2 (ponds) have not been inventoried or characterized in a manner amenable to improving land models. The Permafrost Region Pond and Lake (PeRL) database addresses this problem with a circum-Arctic characterization of ponds and lakes from modern (2002-2013) high-resolution aerial and satellite imagery with a resolution of 5 m or better. We found that ponds are the dominant waterbody type by number in all landscapes.

The Impact
In addition to characterizing waterbody distributions where detailed information exists, we link results with observations of permafrost extent, ground ice volume, geology, and lithology to extrapolate waterbody statistics to regional landscape units. We also provide historical imagers from 1948 to 1965 with a resolution of 6 m or better. These large-scale waterbody distribution estimates, and their temporal trajectories, will help land modelers improve their representation of surface energy and carbon representations, an exercise we are pursuing for the ACME Land Model.

Summary
Waterbodies in Arctic permafrost lowlands strongly affect wetland ecosystem processes of carbon, water, and energy fluxes important in regional- to global-scale models. However, there is no robust theory for the distribution or temporal dynamics of these surface features, nor do land models have accurate characterizations. The open source Permafrost Region Pond and Lake (PeRL) database is a critical first step in developing such theories and model representations. Our findings that small waterbodies dominate the number density of all waterbodies, and that their distributions are temporally dynamic, are motivating ongoing work in conceptualizing process representations that can be integrated in land models to improve prediction of high-latitude terrestrial processes.

Contacts (BER PM)
Daniel Stover, SC-23.1, Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
William J. Riley, Charlie Koven
Lawrence Berkeley National Laboratory
wjriley@lbl.gov, cdkoven@lbl.gov

Funding
William J. Riley and Charles D. Koven were supported by the US Department of Energy, BER, under the NGEE-Arctic project under contract no. DE-AC02-05CH11231.

Publications
Muster, S., ..., W.J. Riley, C.D. Koven, et al. PeRL: A Circum-Arctic Permafrost Region Pond and Lake Database. Earth System Science Data 9, 1-31, doi:10.5194/essd-9-1-2017 (2017). (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 10, 2017

Differences in Soluble Organic Carbon Chemistry in Pore Waters Sampled from Different Pore Size Domains

Protecting soils to mitigate climate change

The Science 
Soil has networks of pores and channels that weave through it like interconnected straws. These networks are formed underground by the different minerals that compose soil and as a result of movements or growth by roots, insects, and other living organisms. Soil pores house gases and liquids such as soil organic carbon (SOC) and water. SOC plays a vital role in the carbon cycle. A recent study found that carbon complexity differs with the size of the pore that contains it, yet its decomposability is driven by its proximity to microorganisms, not its chemistry.

The Impact
These findings could provide a powerful framework for building a new generation of models simulating SOC dynamics and composition. The findings also provide insights for using natural processes to protect SOC so that it remains or decomposes in the soil rather than returning to the atmosphere.

Summary
In the natural water cycle, the hydrologic connectivity of soil pores surges as soil water content increases, and when pore channels fill with water, SOC and other nutrients can mix and redistribute. Furthermore, when the soil is saturated, soil pores become increasingly connected (making them straw-like) by water, allowing movement of dissolved SOC between pores. This movement increases the likelihood that stored carbon will be transported to microbial-rich locations more favorable to decomposition. This diverse distribution of microbial decomposers throughout soil indicates that metabolism or persistence of SOC compounds is highly dependent upon short distances— think “sprints”—of transport between pores, via water, within the soil.

To demonstrate this process, researchers at Pacific Northwest National Laboratory saturated intact soil cores and extracted pore waters with increasing suction pressures to sequentially sample them from increasingly fine-pore domains. The soil solutions were held behind coarse and fine pore “throats,” and revealed more complex soluble carbon in finer pores than in coarser ones. Analysis of the same samples—incubated with fungi Cellvibrio japonicus, Streptomyces cellulosae, and Trichoderma reseei—showed that the more complex carbon in fine pores is not more stable; rather, it is at least as easily decomposed as the simpler forms of carbon found in coarse pores. In fact, the decomposition of complex carbon led to greater losses of it through respiration than the simpler carbon found in coarse pore waters. This finding suggests that repeated cycles of drying and wetting in soils may be accompanied by repeated cycles of increased carbon dioxide emissions. All this raises a question: Is SOC persistence primarily a function of its isolation in different sized pores?

All the study’s incubated samples demonstrated that the fungi could decompose the SOC in pore waters within the first 48 hours of colocation, meaning that the proximity of microbes with the substrate is the controlling factor in protecting carbon within the soil. The challenge is to use this information to improve predictions of carbon persistence in soils and perhaps determine if and how these natural processes within the soil could be exploited on a much bigger scale so that carbon releases to the atmosphere are reduced.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, (301-903-0289); and Jared.DeForest@science.doe.gov, (301-903-1678)

(PI Contact)
Vanessa Bailey
(509) 371-6965, Vanessa.bailey@pnnl.gov

Funding
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research as part of the Terrestrial Ecosystem Science program. A portion of this research was performed using the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility located at Pacific Northwest National Laboratory.

Publication
Bailey, V., et al. 2017. “Differences in Soluble Organic Carbon Chemistry in Pore Waters Sampled from Different Pore Size Domains,” Soil Biology and Biogeochemistry 107, 133-143. DOI: 10.1016/j.soilbio.2016.11.025. Reference link.

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 10, 2017

Large CO2 and CH4 Emissions from Polygonal Tundra During Spring Thaw in Northern Alaska

Findings suggest that the Arctic may be even less of a carbon sink than previously thought.

The Science
A multi-institution team of scientists measured a large pulse of greenhouse gases [carbon dioxide (CO2) and methane (CH4)] released from the frozen Arctic tundra during a two-week period in late May to early June 2014 when soils started to thaw. Little is known about such releases, and the researchers investigated the circumstances, mechanism, likelihood, and outcomes of these events. They show that the pulse was the result of a delayed mechanism, in which gases produced in fall were trapped in the frozen soils and released in spring. The team linked hydrology, biogeochemistry, and geophysics to uncover the pivotal roles of warmer fall weather and spring rain-on-snow events, implying these pulses may be more frequent in the future.

The Impact
The research identified a large, underrepresented source of carbon in the Arctic. The findings suggest that the Arctic may be even less of a carbon sink than previously thought. The eddy covariance measurements imply that to calculate Arctic carbon budgets more accurately, early spring fluxes should be measured and taken into account. The dynamics of this offset in the context of climate change are not yet known, but it appears that the conditions that lead to the accumulation and abrupt emission of the stored gases may become more frequent with warming. 

Summary
Measurements of a large pulse of carbon gases emitted from the tundra ecosystem were made near Barrow, Alaska, in May 2014. The pulse was large enough to offset nearly half of the following summer's net plant CO2 uptake and added 6% to the CH4 summer fluxes. A similar pulse was measured 5 km away, indicating that this was a widespread phenomenon. Examination of an array of field surveys and laboratory experiments indicated that the spring carbon pulse was a result of a delayed mechanism in which gases produced in the fall are trapped in the frozen soils and released in early spring. How do gases accumulate in the soil? As temperatures drop in late fall, the mid-soil layer remains above freezing for approximately a month after the surface layer has frozen. Microbial activity in the mid-layer produced gases that are trapped beneath the surface ice. How are gases rapidly released from the soils in spring? May 2014 was unique in that several rain-on-snow events took place, with the potential to enhance soil cracking. These cracks can serve as pathways for rapid gas release as soon as the surface ice thaws. How will things change in the future? Warmer fall seasons may lead to a longer period of gas accumulation in the soils; more rain-on-snow events in spring may increase the likelihood of spring carbon pulse events.

Contacts (BER PM)
Daniel Stover
SC-23.1
daniel.stover@science.doe.gov, 301-903-0289

PI Contacts
Naama Raz Yaseef
Lawrence Berkeley National Laboratory
nryassef@lbl.gov

Margaret S. Torn
Lawrence Berkeley National Laboratory
mstorn@lbl.gov

Funding
This work was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program's Next-Generation Ecosystem Experiments-Arctic project and Atmospheric System Research program's Atmospheric Radiation project. Snow depth and density were measured with the support of Arctic Landscape Conservation Cooperative, U.S. Fish and Wildlife Service, project number ALCC2012-07.

Publications
Yaseef, N. R., M. S. Torn, Y. Wu, D. P. Billesbach, A. K. Liljedahl, T. J. Kneafsy, V. E. Romanovsky, D. R. Cook, and S. D. Wullschleger. 2017. "Large CO2 and CH4 Emissions from Polygonal Tundra During Spring Thaw in Northern Alaska," Geophysical Research Letters, DOI: 10.1002/2016GL071220. (Reference link)

Hubbard, S. S., et al. 2013. "Quantifying and Relating Land-Surface and Subsurface Variability in Permafrost Environments Using LiDAR and Surface Geophysical Datasets," Hydrogeology Journal 21(1), 149-69. DOI: 10.1007/s10040-012-0939-y. (Reference link)

Song, C., et al. 2012. "Large Methane Emission upon Spring Thaw from Natural Wetlands in the Northern Permafrost Region," Environmental Research Letters 7(3), 34009. DOI: 10.1088/1748-9326/7/3/034009. (Reference link) .

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 03, 2017

Plant-Mycorrhizal Interactions Influence Coexistence Patterns in Plants

The symbiosis between plants and mycorrhizal fungi can change nutrient availability, which can alter how plants interact and coexist.

The Science
The coexistence of plants in an ecosystem is regulated by resource availability and competition for those resources. Mycorrhizal fungi (MF), a root symbiont that helps plants obtain nutrients, can alter how plants compete for resources, which can alter patterns of plant coexistence. MF are found almost everywhere that plants grow, so leaving them out of climate models can cause inaccurate predictions of ecosystem patterns such as plant coexistence. Researchers recently developed a new mathematical model that includes MF for the first time.

The Impact
Because MF alter resource availability, it may seem obvious that they will alter plant coexistence. Until now, however, mathematical models did not include MF. Including MF in models will lead to better predictions, which can enable better understanding of patterns in nature and how they might be altered by climate change.

Summary
Mycorrhizal fungi (MF) can alter plant coexistence patterns by changing the host plant’s ability to compete for resources in the soil. How MF change plant coexistence patterns depends on how dependent the host plant and MF are on one another for survival, the rate at which plants and MF exchange nutrients, and how plant growth patterns respond to the cost-benefit ratio of their symbiotic relationship with MF. A new model, which explicitly includes MF, shows that there are tradeoffs to the symbiosis. At times, the carbon cost of MF is balanced by the increase in nutrient availability; however, it is also possible for the carbon cost to outweigh the nutrient benefits and for MF to become detrimental to the host plant’s growth. The balance of the symbiotic relationship can affect plant competition for resources, which can lead to changes in plant coexistence. This model will enable future empirical studies to form hypotheses in light of a better understanding of MF’s role in plant coexistence patterns.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289); and Jared.DeForest@science.doe.gov (301-903-1678)

(PI Contact)
Aimee T. Classen      
University of Vermont
Aimee.Classen@uvm.edu

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program under award number DE-SC0010562.

Publication
Jiang, J., J. A. M. Moore, A. Priyadarshi, and A. T. Classen. 2017. “Plant-Mycorrhizal Interactions Mediate Plant Community Coexistence by Altering Resource Demand,” Ecology 98, 187-97. DOI: 10.1002/ecy.1630. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


December 15, 2016

Seedling Responses to Climate Warming May Slow Tree Advance Upslope

Warming and provenance limit tree recruitment across and beyond the elevation range of subalpine forest.

The Science                       
Using field experiments in the Rocky Mountains, scientists tested the sensitivity of emerging tree seedlings to artificial warming and watering at three locations along a mountainside to understand whether trees will be able to migrate upward in elevation as the climate changes.

The Impact
Most vegetation models assume that forest trees will track their environmental “niche” as climate warms, including upslope to higher elevations. There is little understanding, however, of climate constraints on seedlings, which are the future of the forest. The unexpected results of intensive field experiments in Colorado indicate that warming reduces the odds of seedlings establishing at and above their current upper limits, as well as in the forest, or provides no net benefit. Seeds sourced from higher elevation trees also performed relatively poorly, suggesting that past genetic adaptation to local conditions may hinder upslope tree advances, a finding counter to current theory.

Summary
Climate warming is expected to promote upslope shifts in forests. However, common gardens sown with seeds collected from two different elevations and subjected to climate manipulations using infrared heaters and manual watering indicate that warming and local genotype may constrain tree seedling recruitment above current treeline. Negative effects of warming in forest, treeline, and alpine sites were partly offset by watering, suggesting growing season moisture may limit establishment of future subalpine forests. Greater climate sensitivity of Engelmann spruce compared with limber pine portends potential contraction in the elevational range of Engelmann spruce and changes in the composition of high-elevation Rocky Mountain forests. The greater availability of poorer quality seed at the upper forest edge could act to further slow upslope shifts.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289) and Jared.DeForest@science.doe.gov (301-903-1678)

(PI Contact)
Lara M. Kueppers
Research Scientist, UC Merced and Lawrence Berkeley National Laboratory
lkueppers@ucmerced.edu or lmkueppers@lbl.gov (510-486-5813)

Funding
This research was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research (DE-FG02-07ER64457).

Publication
Kueppers, L. M., et al. 2016. “Warming and Provenance Limit Tree Recruitment Across and Beyond the Elevation Range of Subalpine Forest,” Global Change Biology, DOI: 10.1111/gcb.13561.

Related Link
Alpine-Treeline Warming Experiment website

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Researchers used infrared heaters and manual watering to manipulate climate, and metal mesh to exclude animals, in a pioneering study on the effects of warming on tree establishment above current treeline limits at Niwot Ridge, CO. Photo: Andrew Moyes. Image reprinted with permission from Kueppers et al., “Warming and provenance limit tree recruitment across and beyond the elevation range of subalpine forest.” Global Change Biology 23, 2383-95 (2017). Copyright 2016 John Wiley & Sons Ltd.



December 08, 2016

Patterns of Tree Mortality in a Temperate Deciduous Forest Derived From a Large Forest Dynamics Plot

Development of a method for characterizing modes of tree mortality to advance understanding and modeling of forest dynamics and the carbon cycle.

The Science
Forest mortality has overriding control on the forest carbon cycle. However, the drivers of mortality in forests are not well understood, and are consequently not well represented in earth system models. In this study, we develop a method for assessing how trees die and how mortality rates differ among species, size classes, and functional groups. The new method will capture rare mortality events and detect mortality events that may be linked to environmental change.

The Impact
We use four censuses of a 25.6 ha ForestGEO forest dynamics plot to assess mortality patterns. With such a large sample size it is possible to characterize mortality rates by size, species, plant functional type, and microhabitat allowing for detailed understanding of the drivers of mortality. The method developed in this paper forms the basis of a protocol now being applied at 10 large-scale tropical ForestGEO plots under the NGEE-Tropics initiative.

Summary
Since understanding fine-scale mortality processes is essential for modeling forest responses to changing climatic and environmental conditions, this work makes important progress in providing empirical observations that will inform future modeling activities in the NGEE-Tropics project. Furthermore, widespread application of annual tree mortality surveys on large forest dynamics plots will provide greater insights into the annual variability of forest structural and compositional changes that result from tree death associated with anthropogenic, ecological, or climatic disturbances.

Contacts
(BER PM)

Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Stuart Davies
ForestGEO-CTFS, Smithsonian Tropical Research Institute
daviess@si.edu

Funding
Funds for the full tree censuses were provided by the Smithsonian Institution Center for Tropical Forest Science-Forest Global Earth Observatory (CTFS-ForestGEO). Annual mortality censuses and the analyses presented here were funded by a Smithsonian Competitive Grants Program in Science award to KAT. CYE received support from the Mary Jean Hale Fund. SJD received support from the Next Generation Ecosystem Experiment (NGEE) Tropics project.

Publications
Gonzalez-Akre, E. B., Meakem, V., Eng, C.Y., Tepley, A. J., Bourg, N. A., McShea, W. J., Davies, S. J. and Anderson-Teixeira, K. J. (2016). Patterns of tree mortality in a temperate deciduous forest derived from a large forest dynamics plot. Ecosphere 7(12): e01595. doi: 10.1002/ecs2.1595

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 28, 2016

Roadmap for Improving the Representation of Photosynthesis in Earth System Models

Researchers identified key model development activities, data needs, and process knowledge improvements required to advance the representation of photosynthesis in next-generation climate models.

The Science 
A collaboration between modelers and plant physiologists compared the projected physiological responses of photosynthesis to key environmental drivers in seven terrestrial biosphere models (TBMs) that form the land components of major Earth system models. The study identified research activities needed to improve process representation of photosynthesis in TBMs.

The Impact
A widely held assumption is that the representation of photosynthesis in TBMs is settled science and that model uncertainty is driven largely by other processes downstream of carbon acquisition. This study demonstrates that model divergence in the physiological response of photosynthesis to key environmental drivers is high and likely a major source of model divergence. This finding is critical because the response of the terrestrial biosphere to global change is driven by these same physiological responses and their accurate representation should be an essential component of improved TBMs. This study lays out the steps needed to improve model representation of photosynthesis.

Summary
Accurate representation of photosynthesis in TBMs is essential for robust projections of global change. However, current representations vary markedly between TBMs, contributing uncertainty to projections of global carbon fluxes. In this study, researchers compared the representation of photosynthesis in seven TBMs by examining leaf and canopy-level responses of photosynthetic carbon dioxide (CO2) assimilation to key environmental variables: light, temperature, CO2 concentration, vapor pressure deficit, and soil water content. They identified research areas where limited process knowledge prevents inclusion of physiological phenomena in current TBMs and research areas where data are urgently needed for model parameterization or evaluation. The study provides a roadmap for new science needed to improve the representation of photosynthesis in the next generation of terrestrial biosphere and Earth system models.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

(PI Contact)
Alistair Rogers
Brookhaven National Laboratory
arogers@bnl.gov

Funding
The New Phytologist Trust provided support of the 9th New Phytologist Workshop: Improving Representation of Photosynthesis in Earth System Models. AR and SPS were supported by the Next-Generation Ecosystem Experiments (NGEE; NGEE-Arctic and NGEE-Tropics) projects funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research through contract number DE-SC00112704 to Brookhaven National Laboratory. DW acknowledges support from the Natural Sciences and Engineering Research Council, Canada Foundation for Innovation, and an Ontario Early Researcher Award. JSD received support from the National Science Foundation (DEB-0955771).

Publications
Rogers, A., B. E. Medlyn, and J. S. Dukes. 2014. “Improving Representation of Photosynthesis in Earth System Models,” New Phytologist 204, 12-14. DOI: 10.1111/nph.12972. (Reference link)

Rogers, A., B. E. Medlyn, J. S. Dukes, G. Bonan, et al. 2017. “A Roadmap for Improving Representation of Photosynthesis in Earth System Models,” New Phytologist 213, 22-42. DOI: 10.1111/nph.14283. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 24, 2016

A Trait-Based Plant Hydraulics Model For Tropical Forests

Developed for use within size-structured models to predict how trees in a forest vary in water status

The Science 
We developed a trait-based plant hydraulics model for tropical forests. It successfully predicts how individual trees in a forest vary in water status based on their size, canopy position and hydraulic traits, which improved simulations of total ecosystem transpiration.

The Impact
A substantial amount of diversity in tropical forests can be represented by a reduced set of model parameters/dimensions.  This sub-model can be used in conjunction with other demographic ecosystem models to predict how forest composition evolves under a changing climate.

Summary
We developed a plant hydraulics model for tropical forests based on established plant physiological theory, in which all parameters of the constitutive equations are biologically-interpretable and measureable plant hydraulic traits (e.g., the turgor loss point, hydraulic capacitance, xylem hydraulic conductivity, water potential at 50% loss of conductivity for both xylem and stomata, and the leaf:sapwood area ratio). Next we synthesized how plant hydraulic traits coordinate and trade-off with each other among tropical forest species. We first show that a substantial amount of trait diversity can be represented in the model by a reduced set of trait dimensions. We then used the most informative empirical trait-trait relationships derived from this synthesis to parameterize the model for all trees in a forest stand. The model successfully captured individual variation in leaf and stem water potential due to increasing tree size and light environment, and also improved simulations of total ecosystem transpiration. Collectively, these results demonstrate the importance of plant hydraulic traits in mediating forest transpiration and overall forest ecohydrology. When used in conjunction with other demographic ecosystem models, this modeling approach can be used to predict how forest composition evolves under a changing climate.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Brad Christoffersen, Chonggang Xu, and Nate McDowell
Brad Christoffersen
Los Alamos National Laboratory
bradley@lanl.gov, 505-665-9118

Funding
This research was supported in part by the European Union Seventh Framework Program under the project AMAZALERT, and by the Next-Generation Ecosystem Experiments (NGEE-Tropics) project, funded by the U.S. Department of Energy, Office of Biological and Environmental Research. Funding was also contributed by the Los Alamos National Laboratory LDRD.

Publications
B. Christoffersen, et al. "Linking hydraulic traits to tropical forest function in a size-structured and trait-driven model (TFS v.1-Hydro)." Geoscientific Model Development Discussions (2016). doi:10.5194/gmd-2016-128.

Related Links
doi:10.5194/gmd-2016-128-supplement
doi:10.15486/NGT/1256473
doi:10.15486/NGT/1256474

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 21, 2016

Tropical Tree Photosynthesis and Nutrients: the Model-Data Connection

Models of phosphorus-limited tropical forests may be improved through empirical relationships between photosynthesis and nutrients.

The Science  
Gas exchange and nutrient content data were collected from upper canopy leaves of 144 trees at two forest sites in Panama, differing in species composition, rainfall, and soil fertility. Relationships between photosynthesis, foliar Nitrogen (N) and Phosphorus (P), and wood density were evaluated against mechanistic and empirical models.

The Impact
This study provides a basis for improving models of photosynthesis based on phosphorus nutrition and thereby increasing the capability of models to predict future conditions in P-limited tropical forests.

Summary
The objective of this study was to analyze and summarize data describing photosynthetic parameters and foliar nutrient concentrations from tropical forests in Panama to inform model representation of phosphorus limitation of tropical forest productivity. Gas exchange and nutrient content data were collected from upper canopy leaves of 144 trees from at least 65 species at two forest sites in Panama, differing in species composition, rainfall, and soil fertility. The relationships between photosynthetic parameters and nutrients were of similar strength for nitrogen and phosphorus and robust across diverse species and site conditions. The strongest relationship expressed maximum electron transport rate (Jmax ) as a multivariate function of both nitrogen and phosphorus, and this relationship was improved with the inclusion of independent data on wood density. Models that estimate photosynthesis from foliar nitrogen content would be improved only modestly with the inclusion of additional data on foliar phosphorus, but doing so may increase the capability of models to predict future conditions in phosphorus-limited tropical forests, especially when combined with data on edaphic conditions and other environmental drivers.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contacts)
Richard J. Norby
Oak Ridge National Laboratory
norbyrj@ornl.gov

Funding
Data collection was supported by ORNL Laboratory Directed Research and Development Program. Data analysis and interpretation were supported by Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics), funded by U. S. Department of Energy, Office of Science.

Publications
R. J. Norby et al. “Informing models through empirical relationships between foliar phosphorus, nitrogen and photosynthesis across diverse woody species in Panama.” New Phytologist (2016). doi: 10.1111/nph.14319 (Reference link)

Related Links
Data posted at http://dx.doi.org/10.15486/NGT/1255260

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 16, 2016

Bacteria Living Within Plant Roots Affect Where and How Plants Allocate Carbon for Growth

Bacteria within plant root tissues influence the size and shape of plant leaves and roots, as well as how plants allocate carbon toward leaves, stems, or roots.

The Science
Plant traits, such as root and leaf area, influence how plants interact with their environment, and bacteria living within plant tissues can determine morphology (plant form and structure) and physiology (how they function). To understand how different microbes shaped plant morphology and physiology, researchers inoculated cottonwood seedlings with three different strains of root-dwelling bacteria. They found that the bacteria did not change photosynthesis rates or total biomass, but bacteria regulated where carbon was allocated and how plants used it. Additionally, the researchers found closely related bacteria can have vastly different effects on plant growth.

The Impact
Since plants interact with their environment through their traits, bacteria may be an important middleman in determining how plants will respond to changing environmental conditions.

Summary
Bacteria living within plant tissues (endophytes) can change how plants express traits such as root and leaf growth rates and the ratio of root to leaves. Small changes in these traits could build up to alter how plants survive, adapt, and compete within their environment. In a recent study, researchers either inoculated cottonwood seedlings with one of three endophytic bacterial stains or left the plant un-inoculated as a control. They then looked at several responses including root and leaf growth rate, plant biomass, photosynthetic rate, and the ratio of roots to leaves. They found that inoculation was linked to an increase in root and leaf growth rate, but that this increase in growth rate did not lead to an increase in plant biomass or photosynthetic efficiency. These findings indicate bacterial endophytes can change where and how carbon is used in a plant, but may not increase the overall amount of carbon fixed by photosynthesis and stored in the plant’s biomass.

Contacts (BER PM)
Daniel Stover, SC-23.1, Daniel.Stover@science.doe.gov, 301-903-0289

(PI Contact)
Aimee T. Classen      
University of Vermont
Aimee.Classen@uvm.edu

Funding
Funding was provided by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research (BER), Genomic Science program as part of the Plant-Microbe Interfaces Scientific Focus Area project at Oak Ridge National Laboratory. Additional funding was provided by BER’s Terrestrial Ecosystem Science program under award number DE-SC0010562.

Publication
Henning, J., et al. 2016. “Root Bacterial Endophytes Alter Plant Phenotype, but not Physiology,” PeerJ  4, e2606. DOI: 10.7717/peerj.2606. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER,SC-23.2 Biological Systems Science Division, BER


November 16, 2016

Underutilized Soil Respiration Data Offer Novel Ways to Constrain and Improve Models

Scientists make a case for using soil respiration data to improve understanding and modeling of ecosystem- to global-scale carbon fluxes.

The Science 
Scientists have spent decades making measurements of soil respiration (RS), the flow of carbon dioxide from the soil to the atmosphere, but only recently have started to collect and synthesize this information. A recent reviewargues that these data offer untapped potential for better understanding the larger carbon cycle and improving the performance of ecosystem- to global-scale computer models.

The Impact
Soil respiration data can bring a range of benefits to model development, particularly with larger databases and improved data-sharing protocols that make RS data more robust and broadly available to the research community. These efforts can help usher in new global syntheses and spark progress in both measurement and modeling of biogeochemical cycles.

Summary
Model-data synthesis activities are increasingly important to understand the carbon and climate systems, but they only rarely have used RS data. In an invited review, Department of Energy researchers at Pacific Northwest National Laboratory and co-authors argue that overlooking RS data is a mistake and identify three major challenges in interpreting and using RS data more extensively and creatively. First, when RS is compared to ecosystem respiration measured from eddy covariance towers, it is not uncommon to find the former to be larger, which is impossible. This finding is most likely because of difficulties in calculating ecosystem respiration, which provides an opportunity to utilize RS for eddy covariance quality control. Second, RS integrates belowground heterotrophic and autotrophic activity (i.e., from plant- and animal-derived carbon), and opportunities exist to use the total RS flux for data assimilation and model benchmarking methods rather than less-certain partitioned fluxes. Finally, RS is generally measured at a different resolution than that needed for comparison to eddy covariance or ecosystem- to global-scale models. Downscaling these fluxes to match the scale of RS, and improving RS upscaling techniques, will improve resolution challenges.

Contacts (BER PM)
Dan Stover and Jared DeForest
Terrestrial Ecosystem Science
Daniel.Stover@science.doe.gov, Jared.DeForest@science.doe.gov

(PI Contact)
Ben Bond-Lamberty
Pacific Northwest National Laboratory
bondlamberty@pnnl.gov  

Funding
ARD acknowledges support from the National Science Foundation (NSF) Advances in Biological Informatics. Funding for AmeriFlux data resources was provided by the U.S. Department of Energy’s Office of Science. RV acknowledges support from the U.S. Department of Agriculture. Ben Bond-Lamberty was supported by the U.S. Department of Energy, Office of Science, Terrestrial Ecosystem Science program. Katherine Todd-Brown was supported by the Linus Pauling Distinguished Postdoctoral Fellowship program, part of the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory. JT was supported by NSF, University of Chicago, and MBL Lillie Research Innovation Award.

Publication
Phillips, C. L., B. Bond-Lamberty, A. R. Desai, M. Lavoie, D. Risk, J. Tang, K. Todd-Brown, and R. Vargas. 2016. “The Value of Soil Respiration Measurements for Interpreting and Modeling Terrestrial Carbon Cycling,” Plant and Soil, DOI: 10.1007/s11104-016-3084-x. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 15, 2016

How Moisture Affects the Way Soil Microbes Breathe

Study models soil-pore features that hold or release carbon.

The Science
Researchers recently studied how moisture influences soil heterotrophic respiration, the process by which microbes convert dead organic carbon in soil to carbon dioxide. Their cost-effective modeling strategy is the first to investigate the effect of moisture on these climate-critical respiration rates at the hard-to-simulate pore scale. The study also finds that simulations must acknowledge the diversity of soil-pore spaces, moving beyond the modeling assumption that they are homogeneous.

The Impact
Globally, soils store enormous quantities of organic carbon, some of which is consumed by microbes and exhaled as carbon dioxide. In this way, soils annually produce a major natural carbon dioxide flux into the atmosphere, in an amount roughly six times larger than human emissions of the same greenhouse gas. Understanding what influences this flux has enormous implications for understanding climate change, the carbon cycle, and setting emissions targets.

Summary
Moisture conditions in soil affect the respiration rate of heterotrophic microbes. Soils are made of sand, silt, clays, and organic matter. Within all this material, miniature "porospheres" interlock to create microbial habitats made of water and gases. Modeling heterotrophic respiration at this "pore scale" is difficult because of two factors: (1) the computational challenges of modeling fluids at this scale and (2) the microscale differences within soil. In every soil, distribution of organic carbon is highly localized and dependent on physical protection, chemical recalcitrance, pore connectivity, nonuniform microbial colonies, and local moisture content.

This study, led by researchers at Pacific Northwest National Laboratory, is the first to conduct a pore-scale investigation of how moisture-driven respiration rates are affected by soil pore structure heterogeneity, soil organic carbon bioavailability, moisture content distribution, and substrate transport. The work provides insight into the physical processes that control how soil respiration responds to changes in moisture conditions. The paper's numerical analyses represent a cost-effective approach for investigating carbon mineralization in soils.

The simulations in this study generally confirmed that the soil respiration rate is a function of moisture content, that such rates increase as moisture (and therefore substrate availability) increases, and that soil respiration decreases after some optimum because of oxygen limitation. The model's results, also replicated by field research, show that respiration rates go up with higher soil porosity, and that compacted soils those with less porosity because they are unplowed and undisturbed - reduce the rate at which carbon dioxide escapes into the atmosphere. The study also warned of a danger to assuming uniform porosity in modeled soils; instead, the researchers found, the structural heterogeneity (diversity) of soils should be modeled as it exists in nature.

Further research is needed to determine how coupled aerobic and anaerobic processes would speed up or slow down the amount of organic carbon sequestered in soil.

Contacts
(BER PM)

Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289) and Jared.DeForest@science.doe.gov (301-903-1678)

(PI Contact)
Vanessa Bailey
Vanessa.bailey@pnnl.gov (509-371-6965)
Chongxuan Liu
Chongxuan.liu@pnnl.gov; liucx@sustc.edu.cn (509-371-6350)

Funding
This research was supported by the U.S. Department of Energy (DOE) Office of Biological and Environmental Research through the Terrestrial Ecosystem Science (TES) program. Part of the research was performed at the Environmental Molecular Sciences Laboratory, a DOE user facility located at Pacific Northwest National Laboratory.

Publication
Z. Yan, et al., "Pore-scale investigation on the response of heterotrophic respiration to moisture conditions in heterogeneous soils." Biogeochemistry 131(1), 121-134 (2106). DOI: 10.1007/s10533-016-0270-0. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Microbes in the soil are central players in converting carbon into greenhouse gases. [Image courtesy Pacific Northwest National Laboratory]



November 15, 2016

Mechanical Vulnerability and Resistance to Snapping and Uprooting for Central Amazon Tree Species

4 April 2017

Tree death associated with wind damage may be explained only by the different wind speeds and gusts direction.

The Science  
Through a tree-pulling experiment we found that tree resistance to failure (uproot or snapping) increased with size (diameter at the breast height, DBH (1.3 m) and above ground biomass, AGB) and differed among species.

The Impact
This mechanistic approach allows the comparison of tree vulnerability and resistance to snapping and uprooting across tropical and temperate forests and facilitates the use of current findings in the context of ecosystem models. Higher wind-induced tree mortality observed on plateaus and top of slopes may be explained by different wind speeds and gusts direction (valleys have different aspects and the wind can blow parallel or perpendicular), rather than by differences in soil-related factors that might effect Mcrit.

Summary
High descending winds generated by convective storms are a frequent and a major source of tree mortality disturbance events in the Amazon, affecting forest structure and diversity across a variety of scales, and more frequently observed in western and central portions of the basin. Soil texture in the Central Amazon also varies significantly with elevation along a topographic gradient, with decreasing clay content on plateaus, slopes and valleys respectively. In this study we investigated the critical turning moments (Mcrit - rotational force at the moment of tree failure, an indicator of tree stability or wind resistance) of 60 trees, ranging from 19.0 to 41.1 cm in diameter at breast height (DBH) and located in different topographic positions, and for different species, using a cable-winch load-cell system. Our approach used torque as a measure of tree failure to the point of snapping or uprooting. This approach provides a better understanding of the mechanical forces required to topple trees in tropical forests, and will inform models of wind throw disturbance. Across the topographic positions, size controlled variation in Mcrit was quantified for cardeiro (Scleronema mincranthum (Ducke) Ducke), mata-matá (Eschweilera spp.), and a random selection of trees from 19 other species. Our analysis of Mcrit revealed that tree resistance to failure increased with size (DBH and ABG) and differed among species. No effects of topography or failure mode were found for the species either separately or pooled. For the random species, total variance in Mcrit explained by tree size metrics increased from an R2 of 0.49 for DBH alone, to 0.68 when both DBH and stem fresh wood density (SWD) were included in a multiple regression model. This mechanistic approach allows the comparison of tree vulnerability induced by wind damage across ecosystems, and facilitates the use of forest structural information in ecosystem models that include variable resistance of trees to mortality inducing factors. Our results indicate that observed topographic differences in windthrow vulnerability are likely due to elevational differences in wind velocities, rather than by differences in soil-related factors that might effect Mcrit.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
G.H.P.M. Ribeiro
gabrielgiga@gmail.com

Funding
Robinson Negrón-Juárez was supported by the Director, Office of Science, Office of Biological and Environmental Research of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 as part of Next-Generation Ecosystems Experiments (NGEE Tropics) and the Regional and Global Climate Modeling (RGCM) and Programs.

Publications
G.H.P.M. Ribeiro, J.Q. Chambers, C.J. Peterson, S.E. Trumbore, D. Magnabosco Marra, C. Wirth, J.B. Cannon, R.I. Négron-Juárez, A.J.N. Lima, E.V.C.M. de Paula, J. Santos, N. Higuchi, “Mechanical vulnerability and resistance to snapping and uprooting for Central Amazon tree species,” Forests Ecology and Management, 380, 1-10, 2016. DOI:10.1016/j.foreco.2016.08.039

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 15, 2016

Understanding Long-Term Trends in Annual Net Ecosystem Exchange of CO2

Slow ecosystem responses conditionally regulate annual carbon balance over 15 years in a Californian oak-grass savanna.

The Science                       
Long-term carbon flux measurements over Mediterranean-type ecosystems enabled observations of ecosystem metabolism responses to a wide range of physical, biological, and ecological conditions. 

The Impact
The study’s findings showed that biotic and abiotic extremes and legacies can introduce variations to annual ecosystem carbon balance. These variations are different from those that might be explained by the fast responses to factors like light and temperature.

Summary
Many ecophysiological and biogeochemical processes respond rapidly to changes in biotic and abiotic conditions, while ecosystem-level responses develop much more slowly (e.g., over months, seasons, years, or decades). To better understand the role of the slow responses in regulating interannual variability in net ecosystem exchange (NEE), the study partitioned NEE into two major ecological terms: gross primary productivity (GPP) and ecosystem respiration (Reco). The researchers tested a set of hypotheses on seasonal scales using flux and environment data collected from 2000 to 2015 in an oak-grass savanna area in California, where ecosystems annually experience a wet winter and spring and 5-month-long summer drought. Results showed that the spring season (April through June) contributed more than 50% of annual GPP and Reco. An analysis of outliers found that each season could introduce significant anomalies in annual carbon budgets. The magnitude of the contribution depends on biotic and abiotic seasonal circumstances across the year and the particular sequences. The study found that (1) extremely wet springs reduced GPP in the years of 2006, 2011, and 2012; (2) soil moisture left from those extremely wet springs enhanced summer GPP; (3) groundwater recharged during the spring of 2011 was associated with the snowpack depth accumulated during the winter between 2010 and 2011; (4) dry autumns (October through December) and winters (January through March) decreased Reco significantly; and (5) grass litter produced in previous seasons might increase Reco, and the effect of litter legacy on Reco was more observable in the second year of two consecutive wet springs. These findings confirm that biotic and abiotic extremes and legacies can introduce variations to annual ecosystem carbon balance, other than those that might be explained by the fast responses.

Contacts (BER PM)
Dennis Baldocchi
University of California, Berkeley
Baldocchi@berkeley.edu

(PI Contact)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

Funding
This research was conducted at AmeriFlux and Fluxnet sites. The research was supported in part by the Office of Science (Terrestrial Carbon Project), U.S. Department of Energy, grant number DE-FG02-03Reco63638; and through the Western Regional Center of the National Institute for Global Environmental Change under cooperative agreement number DE-FC02-03Reco63613. Other sources of support included the Kearney Soil Science Foundation, National Science Foundation, Californian Agricultural Experiment Station, and a Marie Curie International Outgoing Fellowship (European Commission, grant 300083). 

Publications
Ma, S., D. Baldocchi, S. Wolf, and J. Verfaillie. 2016. “Slow Ecosystem Responses Conditionally Regulate Annual Carbon Balance over 15 Years in Californian Oak-Grass Savanna,” Agricultural and Forest Meteorology 228-229, 252-64. DOI: 10.1016/j.agrformet.2016.07.016. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 14, 2016

Temperature Response of Soil Respiration Largely Unaltered with Experimental Warming

Global temperature response of soil respiration is consistent across biomes.

The Science   
A synthesis of 27 experimental warming studies across nine biomes showed that soil respiration increased with temperature to about 25 °C, with rates decreasing with further warming. No acclimation of soil microbes to warming was found.

The Impact
This research suggests that even ecosystems that currently are quite cold, such as tundra, will continue to experience greater soil respiration with forecasted future warming. Also, many single-site studies have shown an acclimation of soil respiration to warming, but acclimation was not found in this much larger, spatially distributed dataset.

Summary
The respiratory release of carbon dioxide from soil is a major, yet poorly understood flux in the global carbon cycle. Climatic warming is hypothesized to increase rates of soil respiration, potentially fueling further increases in global temperatures. However, despite considerable scientific attention in recent decades, the overall response of soil respiration to anticipated climatic warming remains unclear. In this study, researchers synthesized the largest global dataset to date of soil respiration, moisture, and temperature measurements, totaling >3,800 observations representing 27 temperature manipulation studies, spanning nine biomes and over two decades of warming. Their analysis reveals no significant differences in the temperature sensitivity of soil respiration between control and warmed plots in all biomes, with the exception of deserts and boreal forests. Thus, these data provide limited evidence of acclimation of soil respiration to experimental warming in several major biome types, contrary to the results from multiple single-site studies. Moreover, across all non-desert biomes, respiration rates with and without experimental warming follow a Gaussian response, increasing with soil temperature up to a threshold of ~25 °C, above which respiration rates decrease with further increases in temperature. This consistent decrease in temperature sensitivity at higher temperatures demonstrates that rising global temperatures may result in regionally variable responses in soil respiration, with colder climates being considerably more responsive to increased ambient temperatures compared with warmer regions. This analysis adds a unique cross-biome perspective on the temperature response of soil respiration, information critical to improving mechanistic understanding of how soil carbon dynamics change with climatic warming.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

(PI Contact)
Scott D. Bridgham
Institute of Ecology and Evolution
University of Oregon
bridgham@uoregon.edu, 541/346-1466

Funding
Since this is a synthesis of many studies, there were many sources of funding, one of which was the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under grant DE-FG02-09ER604719.

Publication
Carey, J. C., et al. 2016. “Temperature Response of Soil Respiration Largely Unaltered with Experimental Warming,” Proceedings of the National Academy of Sciences (USA), DOI: 10.1073/pnas.1605365113. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 11, 2016

Biogenic Volatile Organic Compounds in Amazonian Ecosystems

Biochemical fingerprints provide clues on tropical forest processes

The Science
Many cellular processes leave unique volatile fingerprints behind that can be studied through the acquisition of gas-phase metabolite profiles in the headspace atmospheres of plants across a wide range of spatial and temporal scales from enzymes to ecosystems and from seconds to seasons. While generally studied for their strong impact on atmospheric properties, recent research results from DOE funded GoAmazon 2014/5 and NGEE Tropics projects in the central Amazon highlight the potential for emissions of volatile metabolites as quantitative tracers of biological processes including carbon and energy metabolism (photosynthesis, photorespiration, respiration, and fermentation), cell wall expansion and growth, acetyl-CoA and fatty acid metabolism and degradation, and antioxidant defense and signaling during abiotic and biotic stress.

The Impact
The emerging field of volatile ecosystem metabolomics integrates chemical, physical, and biological processes involved in the metabolism of volatiles within the land-atmosphere interface including potential perturbations of the system by anthropogenic activities including climate warming. An emerging approach evaluated in this study is the use of volatiles as sensitive ecosystem biomarkers of response to abiotic stress including temperature and drought. Examples include temperature dependent isoprenoid composition and oxidation product formation, senescence and mortality through green leaf volatiles and isoprenoid emissions from storage resins, fermentation volatiles, and volatiles associated with cell wall growth, stress, and repair. The integration of volatiles into plant central metabolism is discussed in term of a predictive understanding of the integration of land processes (plant physiology and biochemistry) with atmospheric processes (atmospheric chemistry and climate). Therefore, volatile metabolomics provides non-invasive techniques to study plant metabolism from a variety of spatial and temporal scales. The application of these methods in the tropics may improve our mechanistic understanding of how environmental and biological variables associated with climate and land use change affect the carbon and energy metabolism of natural and managed forests. Genetic engineering of plant metabolism of volatiles is highlighted as a new research tool with application in enhancing plant productivity and abiotic stress tolerance in agricultural, biofuel, and biomaterial industries.

Summary
Biogenic volatile organic compounds (BVOCs) are produced directly within plants via biochemical pathways associated with primary and secondary metabolic processes. Although non-volatile metabolites are typically bound within specific cellular organelles in lipids or aqueous phases, BVOC volatile metabolites can readily partition between these phases and the intracellular airspace. Thus, many BVOCs may freely exchange among cellular organelles, cells, and tissues, contributing to an integration of whole organism carbon and energy metabolism. Moreover, exchange of the intracellular airspace with the atmosphere may help coordinate the metabolisms of different plants within an ecosystem in response to environmental and biological factors. In addition, land- atmosphere exchange of VOCs integrates local and regional atmospheric chemistry with plant metabolism. In this chapter, select examples of the physiological roles BVOCs in plants is presented with a focus on key results from the DOE funded GoAmazon 2014/5 project in central Amazonia.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Kolby J. Jardine
Climate and Ecosystem Sciences Division (CESD), Lawrence Berkeley National Laboratory (LBNL)
kjjardine@lbl.gov 

Funding
This research was supported as a part of the GoAmazon 2015/6 and NGEE Tropic projects in the central Amazon by the Office of Biological and Environmental Research of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 as part of their Terrestrial Ecosystem Science Program.

Publications
Jardine K and Jardine A, Biogenic volatile organic compounds in Amazonian forest ecosystems (2016) Chapter 4, in "Interactions Between Biosphere, Atmosphere and Human Land Use in the Amazon Basin", Springer, Ecological Studies, Editors: Nagy L., Forsberg B., Artaxo P. DOI:10.1007/978-3-662-49902-3 (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 10, 2016

Aboveground Biomass Variability Across Intact and Degraded Forests in the Brazilian Amazon

Airborne lidar and field inventory data quantify carbon losses from logging and fire in Amazon forests.

The Science  
The authors integrated forest inventory plots and high-density airborne lidar data from 18 regions across the Brazilian Amazon to build a statistical model relating aboveground biomass to lidar metrics across a broad range of degraded forests.  Relatively simple models captured the variation of biomass, including  persistent and significant carbon losses at the most degraded areas.  The authors also found that pantropical maps overestimate carbon stocks in many areas with active logging and burning, and underestimate biomass at intact forests.

The Impact
The impacts of land use and land cover on the carbon cycle are not restricted to deforestation, and this paper identified that carbon losses from logging and fire can be large and persistent: in the most extreme cases biomass was reduced by more than 90% and remain with 40% less biomass than intact forests even 15 year since the last disturbance.  The pantropical biomass maps did not capture these patterns and consistently overestimated biomass in degraded forests.  These maps need frequent updates to capture the rapid changes in biomass in frontier forests.

Summary
The role of tropical forest degradation in the carbon cycle is highly uncertain.  The authors used 359 forest inventory plots co-located with 18,000 ha of airborne lidar data in the Brazilian Amazon and developed statistical models to predict biomass based on airborne lidar metrics of forest structure. Degraded forest areas lost significant portions of their original biomass. The degree of carbon loss was influenced by the intensity of disturbance with a range of more than 90% carbon loss for forests subject to multiple fires to only 4-20% for reduced impact logging.  The authors compared lidar biomass estimates with pantropical maps, and found that these maps consistently overestimated biomass at the most degraded forests and underestimated biomass at intact forests, and failed to capture the fine-scale variability of carbon stocks.  The differences in carbon stocks indicate that the use of such maps in frontier forests leads to significant biases in estimates of baseline carbon stocks, and they should be improved and updated more frequently to better characterize the effects of forest degradation in the carbon cycle.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Michael Keller
International Institute of Tropical Forestry, USDA Forest Service
mkeller.co2@gmail.com 

Funding
Airborne lidar and forest inventory data were acquired by the Sustainable Landscapes Brazil, supported by The Brazilian Agricultural Research Corporation (Embrapa), the US Forest Service, USAID, and the US Department of State, the Brazilian National Council for Scientific and Technological Development (CNPq grants 407366/2013-0, 457927/2013-5), and by NASA Carbon Monitoring System Program (NASA CMSNNH13AW64I). ML was supported by CNPq (grant 151409/2014-5) and the São Paulo State Research Foundation (FAPESP, grant 2015/07227-6).  MK was supported as part of the Next Generation Ecosystem Experiment-Tropics, funded by the US Department of Energy, Office of Science, Office of Biological and Environmental Research. 

Publications
Longo M, Keller M, dos-Santos MN, Leitold V, et al. (2016) Aboveground biomass variability across intact and degraded forests in the Brazilian Amazon. Global Biogeochem. Cycles. 30, 1639-1660. DOI:10.1002/2016GB005465. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 14, 2016

Dynamic Vertical Profiles of Peat Porewater Chemistry in a Northern Peatland

Capturing temporal and spatial variability in porewater chemistry under current conditions establishes a baseline for considering how concentrations, pools, and fluxes may change under future climate scenarios.

The Science
Researchers examined weekly to monthly variation in peat porewater chemistry [pH, cations, nutrients, and total organic carbon (TOC)] depth profiles in an experimental bog in northern Minnesota and compared this temporal variation to spatial (among plot) variation in chemistry.

The Impact
These data provide baseline information on porewater chemistry in the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) experimental bog, highlighting the importance of collecting samples across both space and time. Capturing temporal and spatial variability is needed especially for solute pool and flux calculations and for parameterizing process-based models.

Summary
Research findings showed strong gradients in chemistry depth profiles. For example, ammonium increased and TOC decreased with depth, likely reflecting mineralization of deep peat or TOC. These depth profiles were also temporally dynamic, with ammonium, soluble reactive phosphorus, and potassium concentrations more temporally variable in near-surface porewater than deeper porewater; pH, calcium, and TOC concentrations were more temporally variable at deeper depths. When temporal variation in porewater chemistry at one location was compared to spatial variation in porewater chemistry across 17 locations (SPRUCE plots), findings showed that temporal variation in chemistry at one location was often greater than spatial variation in chemistry, especially in near-surface porewater. These results suggest that representative sampling of porewater requires measurements across both space and time.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

(PI Contact)
Natalie Griffiths
Oak Ridge National Laboratory
griffithsna@ornl.gov / 865-576-3457

Funding
This research was part of the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) project and supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, and the Northern Research Station of the U.S. Department of Agriculture’s Forest Service.

Publication
Griffiths, N. A., and S. D. Sebestyen. 2016. “Dynamic Vertical Profiles of Peat Porewater Chemistry in a Northern Peatland,” Wetlands, DOI: 10.1007/s13157-016-0829-5. (Reference link)

Related Links
SPRUCE

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 12, 2016

Unraveling the Molecular Complexity of Cellular Machines and Environmental Processes

State-of-the-art mass spectrometer delivers unprecedented capability to users.

The Science
Two recent studies demonstrate the enormous potential for scientists to explore extremely complex molecular mixtures and systems frequently encountered in environmental, biological, atmospheric, and energy research.

The Impact
The Environmental Molecular Sciences Laboratory (EMSL), a Department of Energy Office of Science user facility, has an unprecedented ability to routinely analyze large intact proteins, precisely measure the fine structure of isotopes, and extract more information from complex natural organic matter mixtures. One of the world’s most powerful mass spectrometry instruments, a 21 Tesla Fourier transform ion cyclotron resonance mass spectrometer (21T FTICR MS), is now available to the scientific community. Illustrating the power of this new instrument for biogeochemical research, EMSL scientists were able to make over 8,000 molecular formula assignments from dissolved organic matter mixtures using the 21T FTICR MS. In another study, EMSL users rapidly identified and discovered new types of metal-binding molecules known as siderophores, which are produced by bacterial cells.

Summary
As the highest-performance mass spectrometry technique, the FTICR MS has become increasingly valuable in recent years for various research applications. The FTICR MS determines the mass-to-charge ratio of ions by measuring the frequency at which ions rotate in a magnetic field, providing ultra-high resolution and mass measurement accuracy. The 21T FTICR MS, which is one of only two in the world with this high magnetic field strength, went online at EMSL in 2015. In a recent study, a team of EMSL scientists evaluated performance gains produced by this high magnetic field strength. They found this next-generation instrument empowers routine analysis of large intact proteins, precisely measures the fine structure of isotopes, and elicits more information than ever before from complex natural organic matter mixtures. The initial performance characterization of the 21T FTICR MS demonstrates enormous potential for future applications to extremely complex molecular mixtures and systems frequently encountered in environmental, biological, atmospheric, and energy research. Moreover, this unprecedented level of mass resolution and accuracy will help promote widespread use of top-down proteomics—an approach that enables accurate characterization of different protein variants with different biological activity. As a result, this transformative instrument will enable users from around the world to tackle previously intractable questions related to atmospheric, terrestrial, and subsurface processes; microbial communities; biofuel development; and environmental remediation.

BER PM Contact
Paul Bayer, SC-23.1, 301-903-5324

PI Contact
Ljiljana Paša-Tolic
Environmental Molecular Sciences Laboratory
ljiljana.pasatolic@pnnl.gov

Funding
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science user facility, and the "High Resolution and Mass Accuracy Capability" development project at EMSL.

Publications
J. B. Shaw, T.-Y. Lin, F. E Leach III, A. V. Tolmachev, N. Tolic, E. W. Robinson, D. W. Koppenaal, and L. Paša-Tolic, “21 Tesla Fourier transform ion cyclotron resonance mass spectrometer greatly expands mass spectrometry toolbox.” Journal of the American Society for Mass Spectrometry 27(12), 1929-36 (2016). DOI: 10.1007/s13361-016-1507-9. (Reference link)

L. R. Walker, M. M. Tfaily, J. B. Shaw, N. J. Hess, L. Pasa-Tolic, and D. W. Koppenaal, “Unambiguous identification and discovery of bacterial siderophores by direct injection 21 Tesla Fourier transform ion cyclotron resonance mass spectrometry.” Metallomics (2017). DOI: 10.1039/c6mt00201c. (Reference link)

Related Links
Unraveling Molecular Complexity of Natural Systems
Top-down Proteomics: Onward and Upward

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



The 21 Tesla Fourier transform ion cyclotron resonance mass spectrometer will propel the future direction of environmental, biological, atmospheric, and energy research. [Image courtesy Pacific Northwest National Laboratory]



October 11, 2016

Partitioning Controls on Tropical Evergreen Forest Photosynthesis across Timescales

Both environmental and biotic factors regulate tropical forest photosynthesis, with environment explaining short-term (hourly), but not longer-timescale (monthly and yearly) dynamics.

The Science
Tropical forest photosynthesis varies with the environment and with biotic changes in photosynthetic infrastructure, but our understanding of the relative effects of these factors across timescales is limited. Here, we used a statistical model to partition the variability of seven years of eddy covariance derived photosynthesis in a central Amazon evergreen forest into two main causes (i.e. environmental vs. biological), and identified the differential regulation of tropical forest photosynthesis at different timescales.

The Impact
This study has three important implications for the broader ecology, evolutionary biology, plant physiology, and modeling communities: (1) our work challenges modeling approaches that assume tropical forest photosynthesis is primarily controlled by the environment at both short and long timescales; (2) advances ecophysiological understanding of resource limitation (i.e. light vs. water) and the temperature sensitivity of tropical evergreen forest; and (3) highlights the importance of accounting for differential regulation of tropical forest photosynthesis at different timescales and of identifying the underlying feedbacks and adaptive mechanisms.

Summary
Canopy-scale photosynthesis (Gross Ecosystem Productivity, GEP) of a central Amazonian evergreen forest in Brazil was derived from the k67 eddy covariance tower (2002-2005 and 2009-2011) using the standard approach to partition ecosystem respiration from eddy covariance measurements of net ecosystem exchange. We used statistical models to partition the variability of seven-year eddy covariance derived GEP into two causes: variation in environmental drivers (solar radiation, diffuse light fraction, and vapor pressure deficit) and biotic variation in canopy photosynthetic light-use-efficiency. The ‘full' model was driven by both environmental and biotic factors and the ‘Env' model was driven by environmental factors only. The models were trained by using the hourly data of years 2003, 2005, 2009, and 2011, and validated by the independent data of years 2002, 2004, and 2010, including the aggregation to different timescales (i.e. daily and monthly). Our results showed that both models (‘full' vs. ‘Env') simulated photosynthetic dynamics well at hourly timescales; however, when aggregating the model results into other timescales (i.e. daily, monthly, and yearly), the ‘Env' model showed continuous decline in the model performance. By contrast, the ‘full' model consistently simulated the photosynthetic dynamics across all timescales. Our results thus suggest that environmental variables dominate photosynthetic dynamics at shorter-timescales (i.e. hourly to daily) but not at longer-timescale (i.e. monthly and yearly), and highlight the importance of accounting for differential regulation of GEP at different timescales and of identifying the underlying feedbacks and adaptive mechanisms.   

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Lead author contact information  
Jin Wu 
Brookhaven National Laboratory
jinwu@bnl.gov
   
Institutional contact
Alistair Rogers
Brookhaven National Laboratory
arogers@bnl.gov

Funding
J. Wu and B. Christoffersen were supported in part by the Next-Generation Ecosystem Experiment (NGEE-Tropics) project. The NGEE-Tropics project is supported by the Office of Biological and Environmental Research in the Department of Energy, Office of Science.

Publications
Wu J, Guan K, Hayek M, Restrepo-Coupe N, Wiedemann KT, Xu X, Wehr R, Christoffersen BO, Miao G, Silva R, Araujo AC, Oliviera RC, Camargo PB, Monson RK, Huete, AR, Saleska SR. Partitioning controls on Amazon forest photosynthesis between environmental and biotic factors at hourly to interannual timescales. Global Change Biology 23:1240-57 (2017). DOI:10.1111/gcb.13509. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 29, 2016

Soil Moisture Data: When Is There Enough?

Scientists examine long-term measurements of soil moisture, including data from two ARM sites, to determine the observational record length needed for robust statistics.

The Science      
Soil moisture modifies energy and moisture fluxes into the boundary layer, thereby influencing near-surface air temperature, humidity, and boundary layer instability, and, in some cases, determining if, where, or when precipitation occurs. Understanding land-atmosphere interactions driven by soil moisture anomalies is crucial for subseasonal-to-seasonal climate prediction as well as forecasting of extreme climatic events. A recent study looked into how long of a soil moisture record is needed for robust statistics.

The Impact
Existing soil moisture datasets do not have consistent record lengths; therefore, the ability to use these databases for large-scale model validation or investigation of land-atmosphere interaction processes across a range of land types is contingent on properly standardizing soil moisture observations from a variety of in situ sources. This study uses data from 15 long-term measurement sites, including two sites operated by the Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility, to determine what observational record length is sufficient to produce a stable soil moisture distribution. The authors find that between 3 to15 years of data are required to produce stable distributions, with the majority of stations requiring only 3 to 6 years of data. However, more years of data are required to obtain stable estimates of the distribution extremes (5th and 95th percentiles). These results have important implications for the design of soil moisture observational networks and model evaluation studies.

Summary
The ability to use in situ soil moisture for large-scale soil moisture monitoring, model and satellite validation, and climate investigations is contingent on properly standardizing soil moisture observations. Percentiles are a useful method for homogenizing in situ soil moisture. However, few stations have been continuously monitoring in situ soil moisture for 20 years or longer. Therefore, one challenge in evaluating soil moisture is determining whether the period of record is sufficient to produce a stable distribution from which to generate percentiles. In this study, daily in situ soil moisture observations, measured at three separate depths in the soil column at 15 stations in the United States and Canada, are used to determine the record length that is necessary to generate a stable soil moisture distribution. The Anderson-Darling test is implemented, both with and without a Bonferroni adjustment, to quantify the necessary record length. The team evaluates how the necessary record length varies by location, measurement depth, and month. They find that between 3 and 15 years of data are required to produce stable distributions, with the majority of stations requiring only 3 to 6 years of data. Not surprisingly, more years of data are required to obtain stable estimates of the 5th and 95th percentiles than the first, second, and third quartiles of the soil moisture distribution. Similarly, the required number of years increased with depth, with more years necessary for observations taken between 50 and 60 cm than those taken between 20 and 30 cm and 5 and 10 cm depths. Overall, the results suggest that 6 years of continuous, daily in situ soil moisture data are sufficient in most conditions to create stable percentiles. These results may not apply to locations with climatic or edaphic conditions that differ from those used in this study.

Contacts
(BER PM)

Sally McFarlane
ARM Program Manager
Sally.McFarlane@science.doe.gov

(PI Contact)
Trent Ford
Southern Illinois University
twford@siu.edu

Funding
This work used data from the Oklahoma Mesonet network, which is jointly operated by Oklahoma State University and University of Oklahoma. Additional data was provided by the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility (Pawhuska and Lamont, Oklahoma sites). Finally, this work used soil moisture data acquired by the FLUXNET community and, in particular, by Fluxnet-Canada (supported by the Canadian Foundation for Atmospheric Sciences, Natural Sciences and Engineering Council, BIOCAP, Environment Canada, and Natural Resources Canada).

Publication
Ford, T. W., Q. Wang, and S. M. Quiring. 2016. “The Observation Record Length Necessary to Generate Robust Soil Moisture Percentiles,” Journal of Applied Meteorology and Climatology 55(10), 2131-49. DOI: 10.1175/JAMC-D-16-0143.1. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 23, 2016

Soil Will Absorb Less Atmospheric Carbon Than Expected This Century

A recent analysis of carbon isotope data suggests Earth system models overestimate soil carbon sequestration potential.

The Science
Researchers used carbon-14 (14C) data from 157 globally distributed soil profiles to determine that current soil carbon is about 3,100 years old rather than the 450 years stipulated by many Earth system models (ESMs).  This analysis shows that the fifth Coupled Model Intercomparison Project (CMIP5), for example, underestimated the mean age of soil carbon by about a factor of six, resulting in an overestimate of soil carbon sequestration potential by a factor of nearly two. Consequently, a greater fraction of carbon dioxide (CO2) emissions than previously thought could remain in the atmosphere and contribute to global warming.

The Impact
These findings, which have important implications for future atmospheric CO2 levels, emphasize the need to incorporate better understanding of soil carbon cycling as well as 14C and other tracer diagnostics into ESMs to improve the quality of future climate projections. The work also illustrates the potential value of systematically exploiting available ecosystem measurements during model development to create more robust models.

Summary
Soil is the largest terrestrial carbon reservoir and may influence the sign and magnitude of carbon cycle-climate feedbacks. Many ESMs estimate a significant soil carbon sink by 2100, yet the underlying carbon dynamics determining this response have not been systematically tested against observations. Researchers from the University of California, Irvine, Max Planck Institute for Biogeochemistry, Lawrence Berkeley National Laboratory, Stanford University, and U.S. Geological Survey used 14C data from 157 globally distributed soil profiles sampled to 1-meter depth to show that ESMs underestimated the mean age of soil carbon by a factor of more than six (430 ± 50 years versus 3100 ± 1800 years). Consequently, ESMs overestimated the carbon sequestration potential of soils by a factor of nearly two (40 ± 27%). This analysis shows that ESMs must better represent carbon stabilization processes and the turnover time of slow and passive soil carbon reservoirs when simulating future atmospheric CO2 dynamics.

Contacts (BER PM)
Dan Stover,
SC-23.1
Daniel.Stover@science.doe.gov
301-903-0289

Renu Joseph
SC-23.1
Renu.Joseph@science.doe.gov
301-903-9237

(Author Contact)
James T. Randerson
Department of Earth System Science, University of California, Irvine
jranders@uci.edu 949-824-9030

(PI Contacts)
Margaret Torn
Terrestrial Ecosystem Science Scientific Focus Area
Climate and Ecosystem Sciences Division
Lawrence Berkeley National Laboratory
mstorn@lbl.gov  510-495-2223

Forrest Hoffman
Biogeochemistry-Climate Feedbacks Scientific Focus Area
Oak Ridge National Laboratory
forrest@climatemodeling.org  865-576-7680

Funding
This research was performed for the Biogeochemistry-Climate Feedbacks Scientific Focus Area (SFA) and the Berkeley Lab Terrestrial Ecosystem Science (TES) SFA, which are sponsored by the Regional and Global Climate Modeling (RGCM) and TES programs, respectively, in the Climate and Environmental Sciences Division of the Office of Biological and Environmental Research, Office of Science, U.S. Department of Energy.

Publication
Y. He, S. E. Trumbore, M. S. Torn, J. W. Harden, L.J. S. Vaughn, S. D. Allison, and J. T. Randerson, “Radiocarbon constraints imply reduced carbon uptake by soils during the 21st century.” Science 353(6306),1419-24 (2016). [DOI: 10.1126/science.aad4273]

Related Links
Soil will absorb less atmospheric carbon than expected this century UCI-led study finds (UCI Press release)
Biogeochemistry-Climate Feedbacks Scientific Focus Area
Berkeley Lab Scientists Contribute to New Soil Carbon Study Today at Berkeley Lab
Soil sponge soaking up far less carbon dioxide than expected Chemistry Word
Soil will absorb less atmospheric carbon than expected this century, study finds Science Daily
Soil carbon storage not the climate change fix it was thought, research finds The Guardian
The Earth is soaking up less carbon than we thought – which could make it warm up even faster Washington Post

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



A recent analysis finds that soil integrates carbon far slower than thought, meaning the amount that soils can absorb from the atmosphere this century is far less than what is predicted by current Earth system models. [Image courtesy University of California, Irvine]



September 21, 2016

Landscape-Scale Consequences of Differential Tree Mortality from Catastrophic Wind Disturbance in the Amazon

Simple relationships relating tree mortality to disturbance metrics in tropical forests can oversimplify the complex processes that create important variation in tree mortality.

The Science 
Two factors, differential mortality and the spatial structure of mortality, acted independently to affect total necromass (dead plant material) on the landscape. Simple relationships relating tree mortality to disturbance metrics in tropical forests can oversimplify the complex processes that create important variation in tree mortality related to tree and landscape characteristics.

The Impact
Forest carbon loss from wind disturbance is sensitive to not only the underlying spatial dependence of observations, but also the biological differences between individuals that promote differential levels of mortality.

Summary
Wind disturbance can create large forest blowdowns, which greatly reduces live biomass and adds uncertainty to the strength of the Amazon carbon sink. Observational studies from within the central Amazon have quantified blowdown size and estimated total mortality but have not determined which trees are most likely to die from a catastrophic wind disturbance. Also, the impact of spatial dependence upon tree mortality from wind disturbance has seldom been quantified, which is important because wind disturbance often kills clusters of trees due to large treefalls killing surrounding neighbors. We examine (1) the causes of differential mortality between adult trees from a 300-ha blowdown event in the Peruvian region of the northwestern Amazon, (2) how accounting for spatial dependence affects mortality predictions, and (3) how incorporating both differential mortality and spatial dependence affect the landscape level estimation of necromass produced from the blowdown. Standard regression and spatial regression models were used to estimate how stem diameter, wood density, elevation, and a satellite-derived disturbance metric influenced the probability of tree death from the blowdown event. The model parameters regarding tree characteristics, topography, and spatial autocorrelation of the field data were then used to determine the consequences of non-random mortality for landscape production of necromass through a simulation model. Tree mortality was highly non-random within the blowdown, where tree mortality rates were highest for trees that were large, had low wood density, and were located at high elevation. Of the differential mortality models, the non-spatial models over predicted necromass, whereas the spatial model slightly under predicted necromass. When parameterized from the same field data, the spatial regression model with differential mortality estimated only 7.5% more dead trees across the entire blowdown than the random mortality model, yet it estimated 51% greater necromass. We suggest that predictions of forest carbon loss from wind disturbance are sensitive to not only the underlying spatial dependence of observations, but also the biological differences between individuals that promote differential levels of mortality.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Sami W. Rifai
Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK
sami.rifai@ouce.ox.ac.uk

Funding
R. Negrón-Juárez was supported by Next-Generation Ecosystems Experiments-Tropics (NGEE Tropics) and the Regional and Global Climate Modeling (RGCM) program funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research.

Publications
Rifai S, Urquiza Muñoz JD, Negrón-Juárez RI, Ramirez FR, Tello-Espinoza R, Vanderwel MC, Lichstein JW, Chambers JQ, Bohlman SA, Landscape-scale consequences of differential tree mortality from catastrophic wind disturbance in the Amazon, Ecological Applications, 26(7), 2016, pp. 2225-2237. DOI: 10.1002/eap.1368 (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 19, 2016

Evaluating Coupled Carbon and Water Vapor Exchange with Carbon Isotopes in the Community Land Model (CLM4.5)

Stable carbon isotopes allow for the calibration and improvement of land surface models.

The Science
Researchers used continuous observations of stable carbon isotopes that are exchanged between the land and atmosphere to better understand how a forest in the Colorado Rocky Mountains responded to stressful growing conditions.

The Impact
Stable carbon isotopes provide a useful and independent constraint upon stomatal conductance, an important ecosystem parameter that controls carbon and energy balance at the land surface. Isotopes also can help guide improvements in how nitrogen limitation is represented within the land model component of a climate model.

Summary
Researchers used stable carbon isotopes of carbon dioxide (CO2) to improve the performance of a land surface model, a component within Earth system climate models. They found that isotope observations can provide important information related to the exchange of carbon and water from vegetation driven by environmental stress from low atmospheric moisture and rate of carbon assimilation (photosynthetic rate). This information provided by isotope observations can go beyond what has traditionally been provided by land surface exchange of carbon, heat, and water measured from towers. Unexpectedly, the study also found that isotope observations provided guidance on how nitrogen limitation should be represented within models. Therefore, the study concludes that isotopes have a unique potential to improve model performance and provide insight into land surface model development.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289); and Jared.DeForest@science.doe.gov (301-903-1678)

(PI Contact)
David R. Bowling
University of Utah, Department of Biology
David.Bowling@utah.edu (801-581-2130)

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program.

Publication
Raczka, B., H. F. Duarte, C. D. Koven, D. Ricciuto, P. E. Thornton, J. C. Lin, and D. R. Bowling. 2016. “An Observational Constraint on Stomatal Function in Forests: Evaluating Coupled Carbon and Water Vapor Exchange with Carbon Isotopes in the Community Land Model (CLM4.5),” Biogeosciences 13, 5183-204. DOI: 10.5194/bg-13-5183-2016. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 14, 2016

Aquatic Plants Accelerate Arctic Methane Emissions

Climate change has caused a boom in aquatic plant biomass on the Arctic tundra in recent decades. Those plants, in turn, are releasing increasing amounts of methane into the atmosphere.

The Science
Researchers measured methane (CH4) fluxes of aquatic vegetation in 2010-2013 at sites characterized in the 1970s at the International Biological Program (IBP) research site near Barrow, Alaska. They then developed statistical models to determine the major environmental factors associated with CH4 emissions such as plant biomass and active-layer depth. They used the IBP historic datasets to model changes in CH4 fluxes between the 1970s and 2010s. Next, using high-resolution imagery, the researchers mapped aquatic vegetation and applied their model to estimate regional changes in CH4 emissions.

The Impact
The regionally observed increases in plant biomass and active-layer thickening over the past 40 years not only have major implications for energy and water balance, but also have significantly altered land-atmosphere CH4 emissions for this region, potentially acting as a positive feedback to climate warming.

Summary
Plant-mediated CH4 flux is an important pathway for land-atmosphere CH4 emissions, but the magnitude, timing, and environmental controls, spanning scales of space and time, remain poorly understood in arctic tundra wetlands, particularly under the long-term effects of climate change. CH4 fluxes were measured in situ during the peak growing season for the dominant aquatic emergent plants in the Alaskan arctic coastal plain, Carex aquatilis and Arctophila fulva, to assess the magnitude and species-specific controls on CH4 flux. Plant biomass was a strong predictor of A. fulva CH4, flux while water depth and thaw depth were copredictors for C. aquatilis CH4 flux. The researchers used plant and environmental data from 1971 to 1972 from the historic IBP research site near Barrow, Alaska, which they resampled in 2010-2013, to quantify changes in plant biomass and thaw depth. They used these data to estimate species-specific decadal-scale changes in CH4 fluxes. A ~60% increase in CH4 flux was estimated from the observed plant biomass and thaw-depth increases in tundra ponds over the past 40 years. Despite covering only ~5% of the landscape, the researchers estimate that aquatic C. aquatilis and A. fulva account for two-thirds of the total regional CH4 flux of the Barrow Peninsula. The regionally observed increases in plant biomass and active-layer thickening over the past 40 years not only have major implications for energy and water balance, but also have significantly altered land- atmosphere CH4 emissions for this region, potentially acting as a positive feedback to climate warming.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov 301-903-0289 and Jared.DeForest@science.doe.gov 301-903-1678

(PI Contact)
Christian G. Andresen
Los Alamos National Laboratory, Los Alamos, NM
candresen@lanl.gov 505-665-7661

Funding
This research is supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Next-Generation Ecosystem Experiments-Arctic project; and by the National Science Foundation Graduate Research Fellowship Program (NSF-1110312).

Publications
Andresen, C. G., M. J. Lara, C. T. Tweedie, and V. L. Lougheed. 2016. “Rising Plant-Mediated Methane Emissions from Arctic Wetlands,” Global Change Biology, DOI: 10.1111/gcb.13469. (Reference link)

Related Links
EOS article

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 13, 2016

A Belowground Perspective On Forest Drought

Subsurface interactions between roots and soils offer improved predictions for managing climate change impacts.

The Science
Key data on root distributions and soil water potential from prior Department of Energy-funded precipitation manipulations on the Oak Ridge Reservation (Tennessee) were used to illustrate mechanistic modeling needs. Results show challenges and opportunities associated with managing forests under conditions of increasing drought frequency and intensity and provide a belowground perspective on drought that may facilitate improved forest management.

The Impact
The study highlights how a belowground perspective of drought can be used in climate models to reduce uncertainty in predicting ecosystem consequences of droughts in forests.

Summary
Predicted increases in the frequency and intensity of droughts across the temperate biome have highlighted the need to examine the extent to which forests may differ in their sensitivity to water stress. At present, a rich body of literature exists on how leaf- and stem-level physiology influence tree drought responses. Less is known, however, regarding the dynamic interactions that occur belowground between roots and soil physical and biological factors. Consequently, better understanding is needed of how and why processes occurring belowground influence forest sensitivity to drought. This study reviews what is known about tree species’ belowground strategies for dealing with drought, and how physical and biological characteristics of soils interact with rooting strategies to influence forest sensitivity to drought. Findings show how a belowground perspective of drought can be used in models to reduce uncertainty in predicting ecosystem consequences of droughts in forests. Additionally, the researchers describe the challenges and opportunities associated with managing forests under conditions of increasing drought frequency and intensity and explain how a belowground perspective on drought may facilitate improved forest management.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov; Jared.DeForest@science.doe.gov

(PI Contact)
Paul J. Hanson
Oak Ridge National Laboratory, Climate Change Science Institute
Email: hansonpj@ornl.gov

Funding
This work was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research; and National Science Foundation.

Publication
Phillips, R. P., I. Ibanez, L. D’Orangeville, P. J. Hanson, M. G. Ryan, and N. McDowell. 2016.“A Belowground Perspective on the Drought Sensitivity of Forests: Towards Improved Understanding and Simulation,” Forest Ecology and Management 380, 309-20. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 13, 2016

Improving Global Methane Emission Predictions

A multiscale comparison of modeled and observed seasonal methane emissions in northern wetlands.

The Science
Wetlands are the largest global natural methane (CH4) source, yet predictive capability of land models is low. In a recent study, researchers improved the methane module in the Community Land Model (CLM) and Accelerated Climate Modeling for Energy (ACME) Land Model (ALM) and compared predictions with tower and aircraft observations and atmospheric inversions. The findings highlight new observations and model requirements to improve global CH4 predictions.

The Impact
Model changes substantially improved CH4 emission predictions compared to observations. Cold season CH4 emissions estimates remain biased low, motivating more observations during this period. Large CH4 emissions uncertainties also are generated by uncertainties in wetland hydrology.

Summary
The study compared wetland CH4 emission model predictions with site- to regional-scale observations. A comparison of the CH4 fluxes with eddy flux data highlighted needed changes to the model’s estimate of aerenchyma area, which were implemented and tested. The model modifications substantially reduced biases in CH4 emissions when compared with CarbonTracker CH4 predictions. CLM4.5 CH4 emission predictions agree well with Alaskan growing season (May-September) CarbonTracker CH4 predictions and site-level observations. However, the model underestimated CH4 emissions in the cold season (October-April). The monthly atmospheric CH4 mole fraction enhancements due to wetland emissions also were assessed using the Weather Research and Forecasting-Stochastic Time-Inverted Lagrangian Transport (WRF-STILT) model and compared with measurements from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) campaign. Both the tower and aircraft analyses confirm the underestimate of cold season CH4 emissions. The greatest uncertainties in predicting the seasonal CH4 cycle are from the wetland extent, cold season CH4 production, and CH4 transport processes. Predicted CH4 emissions remain uncertain, but the study’s findings show that benchmarking against observations across spatial scales can inform model structural and parameter improvements.

Contacts (BER PM)
Daniel Stover, Jared DeForest, and Renu Joseph
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; Jared.DeForest@science.doe.gov, 301-903-1678; and renu.joseph@science.doe.gov, 301-903-9237

(PI Contact)
William J. Riley
Lawrence Berkeley National Laboratory
wjriley@lbl.gov

Funding
Funding for this study was provided by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, under the Regional and Global Climate Modeling program and Next-Generation Ecosystem Experiments–Arctic project under contract # DE-AC02-05CH11231.

Publication
Xu, X., W. J. Riley, C. D. Koven, et al. 2016. “A Multiscale Comparison of Modeled and Observed Seasonal Methane Emissions in Northern Wetlands,” Biogeosciences 13, 5043-56. DOI: 10.5194/bg-13-5043-2016. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 12, 2016

Biogeochemical Modeling of CO2 and CH4 Production in Anoxic Arctic Soil Microcosms

Approach adds explicit aquatic phase redox and pH to a decomposition cascade model.

The Science
Explicit aqueous phase redox, pH, and mineral interaction dynamics were coupled to the Converging Trophic Cascade (CTC) decomposition model, enabling prediction of carbon dioxide (CO2) and methane (CH4) production from Arctic polygonal tundra soils under laboratory incubations over a range of temperatures.

The Impact
The extended model captures pH dynamics reasonably well in Arctic soil incubations. Temperature and pH sensitivity for microbial reactions is highlighted as an important area for further research.

Summary
Soil organic carbon turnover and CO2 and CH4 production are sensitive to redox potential and pH. However, land surface models typically do not explicitly simulate the redox or pH, particularly in the aqueous phase, introducing uncertainty in greenhouse gas predictions. To account for the impact of availability of electron acceptors other than oxygen (O2) on soil organic matter (SOM) decomposition and methanogenesis, researchers extended an existing decomposition cascade model (Converging Trophic Cascade model or CTC) to link complex polymers with simple substrates and add iron [Fe(III)] reduction and methanogenesis reactions. Because pH was observed to change substantially in the laboratory incubation tests and in the field and is a sensitive environmental variable for biogeochemical processes, the researchers used the Windermere Humic Aqueous Model (WHAM) to simulate pH buffering by SOM. To account for the speciation of CO2 among gas, aqueous, and solid (adsorbed) phases under varying pH, temperature, and pressure values, as well as the impact on typically measured headspace concentration, they used a geochemical model and an established reaction database to describe observations in anaerobic microcosms incubated at a range of temperatures (-2, +4, and +8 °C). The study’s results demonstrate the efficacy of using geochemical models to mechanistically represent the soil biogeochemical processes for Earth system models. The modeling approach demonstrated in this work will be evaluated against additional field and laboratory data and incorporated in new Earth system modeling development to improve prediction of greenhouse gas fluxes in Arctic tundra environments.

Contacts (BER PM)
Daniel Stover, Jared DeForest, and Dorothy Koch
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289); Jared.DeForest@science.doe.gov (301-903-1678); and Dorothy.Koch@science.do.egov (301-903-0105)

(PI Contact)
Peter E. Thornton, Environmental Science Division and Climate Change Science Institute, Oak Ridge National Laboratory. thorntonpe@ornl.gov, 865-241-3742

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Oak Ridge National Laboratory Terrestrial Ecosystem Science Scientific Focus Area and Earth System Modeling (Accelerated Climate Model for Energy project).

Publication
Tang, G., J. Zheng, X. Xu, Z. Yang, D. E. Graham, B. Gu, S. Painter, and P. E. Thornton. 2016. “Biogeochemical Modeling of CO2 and CH4 Production in Anoxic Arctic Soil Microcosms,” Biogeosciences 13, 5021-41. DOI: 10.5194/bg-13-5021-2016. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 01, 2016

Alaska Arctic Vegetation Archive

A database of vegetation data from the Alaskan Arctic tundra is now publicly available.

The Science
The Arctic Vegetation Archive (AVA) was developed in response to a goal set by the intergovernmental Arctic Council of eight Arctic nations to better understand the biodiversity and distribution of vegetation across the circumpolar Arctic.

The Impact
An intergovernmental partnership to compile available arctic vegetation data can be leveraged to quantify and model the biodiversity and distribution of vegetation across the Arctic, now and in the future.

Summary
The AVA was conceived by the Flora Group of the Conservation of Arctic Flora and Fauna (CAFF), the biodiversity working group of the intergovernmental Arctic Council, with the goal of compiling available plot-level vegetation data to better understand the distribution of vegetation across the Arctic tundra. Each Arctic nation is tasked with developing a portion of the evolving pan-Arctic vegetation archive. The U.S. contribution, the Alaska Arctic Vegetation Archive (AVA-AK), was begun in 2013. To date, the AVA-AK contains more than 3,000 non-overlapping vegetation plots from the Arctic portion of Alaska, with georeferenced locations and associated environmental data ranging from slope and altitude, to edaphic conditions, to plot-level microrelief (i.e., microtopography as in basically just small-scaled features). Plant species in the AVA-AK encompass both vascular and nonvascular plants and span Arctic vegetation communities ranging from wet tundra to dwarf shrubs to alpine communities to snowbeds. The AVA-AK database is freely available through a web-based portal at the Alaska Arctic Geoecological Atlas (http://alaskaaga.gina.alaska.edu) housed at the University of Alaska, Fairbanks. A preliminary cluster analysis of the data in the AVA-AK indicates the database can be used to predict patterns of vegetation composition across Alaskan tundra in relation to soil moisture and acidity, geography, and ecological affiliation. Furthermore, data in the AVA-AK can provide a baseline of vegetation distribution across Arctic Alaska for use in terrestrial biosphere models. The Department of Energy’s Next-Generation Ecosystem Experiments–Arctic (NGEE-Arctic) project joined this international collaboration and contributed species and functional type cover, along with habitat and edaphic conditions, from vegetation censuses conducted during Phase 1 of NGEE-Arctic at Intensive Site 1 on the Barrow Environmental Observatory in Barrow, Alaska. In Phase 2, NGEE-Arctic will contribute data from the Seward Peninsula, Alaska, to help address existing gaps in the AVA-AK database (e.g., large areas of Arctic Alaska not associated with permanent Arctic observatories).  

PI Contacts
Amy L. Breen
Assistant Research Professor
Scenarios Network for Alaska & Arctic Planning
International Arctic Research Center, University of Alaska
PO Box 757340
Fairbanks, Alaska 99775-7340
Phone: (907) 750-1311
E-mail: albreen@alaska.edu

Colleen M. Iversen
Senior Scientist
Climate Change Science Institute and
Environmental Sciences Division
Oak Ridge National Laboratory
One Bethel Valley Road, Bldg. 4500N
Oak Ridge TN 37831-6301
Phone: (865) 241-3961
iversencm@ornl.gov

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

Funding
This work was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science as part of the Next-Generation Ecosystem Experiments–Arctic project and the National Aeronautics and Space Administration’s Arctic Boreal Vulnerability Experiment.

Publications
Walker, D. A., A. L. Breen , L. A. Druckenmiller, L. W. Wirth, W. Fisher, M. K. Raynolds, J. Sibík, M. D. Walker, S. Hennekens, K. Boggs, T. Boucher, M. Buchhorn, H. Bültmann, D. J. Cooper, F. J. A. Daniëls, S. J. Davidson, J. J. Ebersole, S. C. Elmendorf, H. E. Epstein, W. A. Gould, R. D. Hollister, C. M. Iversen, M. T. Jorgenson, A. Kade, M. T. Lee, W. H. MacKenzie, R. K. Peet, J. L. Peirce, U. Schickhoff, V. L. Sloan, S. S. Talbot, C. E. Tweedie, S. Villarreal, P. J. Webber, and D. Zona. 2016. “The Alaska Arctic Vegetation Archive (AVA-AK),” Phytocoenologia, DOI: 10.1127/phyto/2016/0128. (Reference link)

Sloan, V. L., J. D. Brooks, S. J. Wood, J. A. Liebig, J. Siegrist, C. M. Iversen, and R. J. Norby. 2014. “Plant Community Composition and Vegetation Height, Barrow, Alaska, Ver. 1.” Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory (Next-Generation Ecosystem Experiments-Arctic Data Collection), Oak Ridge, TN. DOI: 10.5440/1129476. (Reference link)

Related Links
Alaska Arctic Geoecological Atlas
NGEE Arctic
Global Index of Vegetation-Plot Databases
VegBank
Arctic-Boreal Vulnerability Experiment

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 27, 2016

Global Model Improved by Incorporating New Hypothesis for Vegetation Nutrient Limitation

Low-cost experiment provides first robust test of alternative hypotheses regarding short-term vegetation response to chronic nutrient limitation.

The Science
An innovative and low-cost field experiment provided new results regarding the fundamental process of photosynthetic carbon uptake in the face of varying levels of nutrient limitation. Experimental results refute the current modeling approach for instantaneous downregulation of carbon uptake and support a new hypothesis for long-term storage and release of excess carbon.

The Impact
This new hypothesis has a significant impact on seasonal cycle of atmospheric carbon dioxide (CO2), an important performance metric for global carbon cycle models. The fate of excess carbon can have significant impact on other ecosystem processes.

Summary
Models predicting ecosystem CO2 exchange under future climate change rely on relatively few real-world tests of their assumptions and outputs. This work demonstrated a rapid and cost-effective method to estimate CO2 exchange from intact vegetation patches under varying atmospheric CO2 concentrations. Findings showed that net ecosystem CO2 uptake (NEE) in a boreal forest rose linearly by 4.7 ± 0.2% of the current ambient rate for every 10 ppm CO2 increase, with no detectable influence of foliar biomass, season, or nitrogen fertilization. The lack of any clear short-term NEE response to fertilization in such a nitrogen-limited system is inconsistent with the instantaneous downregulation of photosynthesis formalized in many global models. Incorporating an alternative mechanism with considerable empirical support—diversion of excess carbon to storage compounds—into an existing Earth system model brings the model output into closer agreement with the field measurements. A global simulation incorporating this modified model reduced a long-standing mismatch between the modeled and observed seasonal amplitude of atmospheric CO2. Wider application of this chamber approach would provide critical data needed to further improve modeled projections of biosphere-atmosphere CO2 exchange in a changing climate.

Contacts (BER PM)
Dorothy Koch, Daniel Stover, and Jared DeForest
Dorothy.Koch@science.doe.gov (301-903-0105), Daniel.Stover@science.doe.gov (301-903-0289), and Jared.DeForest@science.doe.gov (301-903-1678)

PI Contact
Peter E. Thornton
Environmental Sciences Division and Climate Change Science Institute
Oak Ridge National Laboratory
thorntonpe@ornl.gov (865-241-3742)

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Earth System Modeling (ACME project) and Oak Ridge National Laboratory Terrestrial Ecosystem Science Scientific Focus Area.

Publication
Metcalfe, D. B., D. Ricciuto, S. Palmroth, C. Campbell, V. Hurry, J. Mao, S. G. Keel, S. Linder, X. Shi, T. Näsholm, K. E. A. Ohlsson, M. Blackburn, P. E. Thornton, and R. Oren. 2016. “Informing Climate Models with Rapid Chamber Measurements of Forest Carbon Uptake,” Global Change Biology, DOI: 10.1111/gcb.13451. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 22, 2016

The Energetic and Carbon Economic Origins of Leaf Thermoregulation

The Science 
The research described in this paper uses a variety of global datasets to support theory suggesting that plants maximize carbon gain, in part, via myriad traits that regulate temperature near the optimum for photosynthesis. 

The Impact
This paper provides the first large advance in our understanding of leaf thermoregulation, and is thus likely to be tested widely.

Summary
Leaf thermoregulation has been rarely documented, and its control is unknown. However, leaf temperature is one of the most critical parameters regulating photosynthesis in Earth System Models. Improving its understanding has widespread fundamental and applied (e.g., modeling) value. We tested a novel carbon and energy-based theory using multiple global datasets of leaf temperature and photosynthesis, along with myriad leaf traits. The theory was supported by the data, and demonstrated that leaf thermoregulation does act to maximize photosynthesis. This paper has broad implications for fundamental biology and for applied modeling of ecosystems.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Nate McDowell
Pacific Northwest National Lab
nate.mcdowell@pnnl.gov

Funding
Funding was provided by DOE, Office of Science, NGEE-Tropics, via LANL LDRD, via NSF, and via the Aspen Center for Environmental Studies. 

Publications
Michaletz, S.T., Weiser, M.D., McDowell, N.G., Zhou, J., Kaspari, M., Helliker, B.R. and Enquist, B.J., 2016. The energetic and carbon economic origins of leaf thermoregulation. Nature Plants, 2, p.16129. DOI:10.1038/nplants.2016.129.

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 20, 2016

Characterizing Peatland Uptake and Losses of Carbon

Community-level flux methods provide a foundation for understanding bog carbon cycle warming responses.

The Science 
Researchers evaluated seasonal patterns of net carbon dioxide (CO2) and methane (CH4) flux from an experimental bog in northern Minnesota to establish a baseline for whole-ecosystem warming studies.

The Impact
Community-level methods were developed and shown capable of quantifying the net flux of the important greenhouse gases CO2 and CH4 in a raised bog setting to capture heterogeneous conditions. These methods enable intact assessments of net ecosystem exchange of carbon from the bog community in a manner that does not disturb the experimentally manipulated plots.

Summary
Evaluation of the net carbon flux from peatlands under a warming global climate is key to the projection of future greenhouse gas emissions to the atmosphere. The method developed in this study, as part of the Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) experiment, enabled these measurements as well as an estimation of seasonal carbon flux of CO2 and CH4 for a temperate bog ecosystem.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov

(PI Contact)
Paul J. Hanson
hansonpj@ornl.gov

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program; and Graduate Fellowship Program (DE-AC05-06OR23100 to A. L. G.).

Publication
Hanson, P. J., A. L. Gill, X. Xu, J. R. Phillips, D. J. Weston, R. K. Kolka, J. S. Riggs, and L. A. Hook. 2016. “Intermediate Scale Community-Level Flux of CO2 and CH4 in a Minnesota Peatland: Putting the SPRUCE Project in a Global Context,” Biogeochemistry 129(3), 255-72. DOI: 10.1007/s10533-016-0230-8. (Reference link)

Related Link
SPRUCE

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 13, 2016

Strong Atmospheric 14C Signature of Respired CO2 Observed over Midwestern United States

Terrestrial biosphere contributes a higher amount of atmospheric CO2 than predicted by an ecosystem model.

The Science
A recent study demonstrates a novel methodology for constraining the net exchange of CO2 between the landscape and atmosphere using 14CO2 observed from a tall tower in the midwestern United States. Exchanges include net ecosystem respiration (including belowground carbon), fires, and anthropogenic sources.

The Impact
The study determined that soil respiration of carbon drives variability in 14CO2 during the summer months and that simulations from the Carnegie-Ames-Stanford Approach (CASA) model underestimate the biospheric 14CO2 source compared to observations at the Wisconsin Tall Tower. This approach has the potential to better constrain the long-term carbon balance of terrestrial ecosystems and the short-term impact of disturbance-based loss of carbon to the atmosphere, and highlights areas for continued land-surface/biogeochemistry model development. 

Summary
A recent study found that during the summer months the biospheric component dominates the atmospheric 14CO2 budget at the Park Falls AmeriFlux/WLEF Tall Tower in northern Wisconsin. Respiration of carbon from soils is an important component of the global carbon cycle, returning carbon previously taken up via photosynthesis over decadal time scales back to the atmosphere. For 2010, observations from 400 m aboveground indicate that the terrestrial biosphere was responsible for a 2 to 3 times higher contribution to total 14CO2 than predicted by the CASA terrestrial ecosystem model. This finding indicates that the model is underpredicting ecosystem respiration and net primary production. Based on back-trajectory analyses, this bias likely includes a substantial contribution from the North American boreal ecoregion, but transported biospheric emissions from outside the model domain cannot be ruled out. The 14CO2 enhancement also appears somewhat decreased in observations made over subsequent years, suggesting that 2010 may be anomalous. Going forward, this isotopic signal could be exploited as an important indicator to better constrain both the long-term carbon balance of terrestrial ecosystems and the short-term impact of disturbance-based loss of carbon to the atmosphere.

BER PM Contacts
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289); and Jared.DeForest@science.doe.gov (301-903-1678)

PI Contacts
Karis McFarlane
Lawrence Livermore National Laboratory
kjmcfarlane@llnl.gov (925-423-6285)

Brian LaFranchi
Now at Aclima
brian.lafranchi@gmail.com (802-310-7083)

Tom Guilderson
Lawrence Livermore National Laboratory
guilderson1@llnl.gov (925-422-1753)

Funding
This work was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Climate and Environmental Science Division, Terrestrial Ecosystem Science program (SCW1447); Lawrence Livermore National Laboratory Lab Directed Research and Development (ERD-14-038); National Oceanic and Atmospheric Administration (NOAA) ESRL Global Monitoring Division; and NOAA Climate Program Office's Atmospheric Chemistry, Carbon Cycle.

Publication
LaFranchi, B. W., K. J. McFarlane, J. B. Miller, S. J. Lehman, C. L. Phillips, A. E. Andrews, P. P. Tans, H. Chen, Z. Liu, J. C. Turnbull, X. Xu, and T. P. Guilderson. 2016. “Strong Regional Atmospheric 14C Signature of Respired CO2 Observed from a Tall Tower over the Midwestern United States,” Journal of Geophysical Research: Biogeosciences 122(8), 2275-95. DOI: 10.1002/2015JG003271. (Reference link)

Related Links
LEF Tower Data

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 11, 2016

Coupled Simulations of Surface and Subsurface Thermal Hydrology in Permafrost-Affected Regions

New multiphysics simulation capability improves permafrost thermal hydrology projections.

The Science
Researchers developed and demonstrated a new process-rich simulation capability for coupled surface and subsurface thermal hydrology in permafrost regions. The Arctic Terrestrial Simulator (ATS) represents nonisothermal surface flow, subsurface thermal hydrology, phase change, surface energy balance, and snow distribution in fully coupled three-dimensional (3D) simulations. 

The Impact
Existing permafrost thermal hydrology simulation tools are limited in their capability to represent the thermal effects of surface and subsurface flows and other important thermal processes. This new process-rich, fine-scale model dramatically expands the range of permafrost thermal hydrology phenomena that can be represented in simulations and provides a community modeling tool to help advance process understanding and evaluate approximations used in Earth system models.

Summary
ATS is a collection of physics modules and physics-informed model couplers for use in a parallel, open-source subsurface flow and transport simulator called Amanzi-ATS. A team of researchers developed new models for nonisothermal overland flow and snow distribution in microtopography, new approaches for robustly coupling 2D surface and 3D subsurface models, and new strategies for managing complexity in process-rich simulations. They combined those new capabilities with a state-of-the-art model for thermal hydrology of freezing and thawing soil. Fine-scale, 100-year projections of the integrated permafrost thermal hydrological system in polygonal tundra near Barrow, Alaska, demonstrate the feasibility of microtopography-resolving, process-rich simulations as a tool to help understand possible future evolution of the carbon-rich Arctic tundra in a warming climate.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

 (PI Contact)
Scott L. Painter
Climate Change Science Institute and Environmental Sciences Division
Oak Ridge National Laboratory
paintersl@ornl.gov, 865-241-2644

Funding
This work was supported by the Next-Generation Ecosystem Experiments (NGEE-Arctic) project. NGEE-Arctic is funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program.   

Publication
Painter, S. L., E. T. Coon, A. L. Atchley, M. Berndt, R. Garimella, J. D. Moulton, D. Svyatskiy, and C. J. Wilson. 2016. “Integrated Surface/Subsurface Permafrost Thermal Hydrology: Model Formulation and Proof-of-Concept Simulations,” Water Resources Research 52(8), 6062-77. DOI: 10.1002/2015WR018427. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 29, 2016

Assessing Challenges and Benefits of an Online “Open Experiment”

PNNL scientists explore a new model for research and data sharing.

The Science
Scientists conducted an “open experiment” in which every aspect of a laboratory experiment was documented online and in real time. This model pushed the researchers to write higher-quality analysis code, shortened the time required to do so, enabled them to quickly identify problems, and resulted in a stronger publication.

The Impact
Researchers in every field of science are being pushed—by funders, journals, governments, and their peers—to increase the transparency and reproducibility of their work. A key part of this effort is a move toward open data as a way to fight post-publication data loss, improve data and code quality, enable powerful meta- and cross-disciplinary analyses, and increase public trust in, and the efficiency of, publicly funded research. The approach used in this study is a way to help researchers achieve these goals and may serve as a model for others.

Summary
In early 2015, Department of Energy scientists at Pacific Northwest National Laboratory planned a laboratory incubation experiment to characterize the chemical and biological properties of sub-Arctic, active-layer soils subjected to changes in temperature and moisture. This experiment required (1) a multidisciplinary team that was not located in one time zone; (2) integration of various data; (3) rapid performance of quality control and diagnostics, so that if instrument problems arose the team would lose only the minimum amount of time and data; and (4) tight integration of data, statistical analyses, and manuscript results. The team designed a data processing and analytical system written in an open-source and widely used language for statistical computing and graphics, and placed it in a publicly available “repository” that stored all code and data, making them available in real time. Using an automated analytical pipeline in an open repository provided significant advantages for the project, but the costs of such an approach and investments required should also be considered.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

(PI Contact)
Ben Bond-Lamberty
Pacific Northwest National Laboratory
bondlamberty@pnnl.gov

Funding
This research was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program.

Publication
Bond-Lamberty, B., P. Smith, and V. Bailey. 2016. “Running an Open Experiment: Transparency and Reproducibility in Soil and Ecosystem Science," Environmental Research Letters 11(8), 084004. DOI: 10.1088/1748-9326/11/8/084004. (Reference link)

Related Links
https://github.com/bpbond/cpcrw_incubation

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 16, 2016

Separating The Effects Of Vegetation Phenology And Diffuse Radiation On Land Carbon Uptake

The effects of clouds and aerosols on land carbon uptake may be less than previously thought.

The Science      
Understanding future climate change requires understanding the full carbon cycle, including how much carbon is taken up by plants over their life cycles, and how that carbon uptake might change with variations in aerosol or cloud conditions. Carbon uptake by plants is often observed to be higher under diffuse radiation associated with clouds and aerosols, implying an effect of these scattering agents on terrestrial gross primary productivity (GPP, which is related to the rate at which photosynthesis occurs).  However, the mechanisms underlying the statistical correlation between diffuse radiation and GPP remain uncertain, and the magnitude of the inferred effect varies widely across studies. In this study, scientists showed that the frequently reported enhancement of plant primary productivity by diffuse radiation associated with clouds and aerosols is mainly due to seasonal changes in plant lifecyle (known as phenology) rather than to radiation quality.

The Impact
Scientists funded by the Department of Energy’s (DOE) Atmospheric System Research program used atmospheric measurements from DOE’s Atmospheric Radiation Measurement (ARM) Climate Research Facility and theoretical modeling to provide new insights into the mechanisms linking diffuse radiation and GPP. They found that diffuse radiation effects on GPP were smaller after accounting for the statistical covariation between diffuse radiation and vegetation phenology. The confounding influence of phenology was confirmed in a canopy photosynthesis and radiative transfer model, suggesting that the effects of diffuse radiation on GPP may have been overestimated in previous studies. These findings address an important land-atmosphere coupling effect, sharpen understanding of the mechanisms linking climate and the carbon cycle, and help inform needed improvements in Earth system models.

Summary
GPP has been reported to increase with the fraction of diffuse solar radiation, for a given total irradiance. The correlation between GPP and diffuse radiation suggests there are effects of diffuse radiation on canopy light-use efficiency, but potentially confounding effects of vegetation phenology have not been fully explored. The scientists applied several approaches to control for phenology, using 8 years of eddy-covariance measurements of winter wheat at the ARM Climate Research Facility Southern Great Plains site in Oklahoma. The apparent enhancement of daily GPP due to diffuse radiation was reduced from 260 percent to 75 percent after subsampling over the peak growing season or by subtracting a 15-day moving average of GPP, suggesting that phenology played a role in the apparent diffuse radiation effect. The diffuse radiation effect was further reduced to 22 percent after normalizing GPP by a spectral reflectance index to account for phenological variations in leaf area index and canopy photosynthetic capacity. Canopy photosynthetic capacity covaries with diffuse fraction at a given solar irradiance at this site because both factors are dependent on day of year, or solar zenith angle. Using a two-leaf sun-shade canopy radiative transfer model, the team confirmed that the effects of phenological variations in photosynthetic capacity can appear qualitatively similar to the effects of diffuse radiation on GPP, and therefore can be difficult to distinguish using observations and simple correlations. The importance of controlling for plant phenology when inferring diffuse radiation effects on GPP raises new challenges and opportunities for using radiation measurements to improve carbon cycle models.

Contacts (BER PM)
Ashley Williamson
SC-23.1, ASR Program Manager
ashley.williamson@science.doe.gov

Shaima Nasiri
SC-23.1, ASR Program Manager
shaima.nasiri@science.doe.gov

Sally McFarlane
SC-23.1, ARM Program Manager
sally.mcfarlane@science.doe.gov

(PI Contact)
Margaret Torn
Lawrence Berkeley National Laboratory
mstorn@lbl.gov

Funding
This research was supported by the Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research under contract number DE-AC02-05CH11231 as part of the Atmospheric System Research and Regional and Global Climate Modeling programs and used data provided by DOE’s Atmospheric Radiation Measurement Climate Research Facility.

Publications
Williams, I. N., W. J. Riley, L. M. Kueppers, S. C. Biraud, and M. S. Torn. 2016. “Separating the Effects of Phenology and Diffuse Radiation on Gross Primary Productivity in Winter Wheat,” Journal of Geophysical Research Biogeosciences 121(7), 1903-15. DOI: 10.1002/2015JG003317. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 14, 2016

Phosphorus Feedbacks May Constrain Tropical Ecosystem Responses to Changes in Atmospheric CO2

The Science
Phosphorus (P) has been generally considered to be the most limiting nutrient in lowland tropical forests. Several recent field studies in the Amazonia have highlighted the importance of P in tropical forest productivity and function. Despite the importance of P in tropical carbon cycling, most Earth System Models don't currently include P cycling and P limitation.  In this study, we investigate how P cycling dynamics might affect tropical ecosystem responses to changes in atmospheric CO2 and climate using a P-enabled land surface model.

The Impact
This study shows that the coupling of P cycle in land surface model results in a more realistic spatial pattern of simulated ecosystem productivity in the Amazon region. Through exploratory simulations, this study points to the need for more tropical field measurements under different temperature/humidity conditions with different soil P availability. 

Summary
It is being increasingly recognized that carbon-nutrient interactions play important roles in regulating terrestrial carbon cycle responses to increasing CO2 in the atmosphere and climate change. Nitrogen-enabled models in CMIP5 showed that accounting for nitrogen greatly reduces the negative feedback between land ecosystems and atmospheric CO2. None of the CMIP5 models has considered P as a limiting nutrient, although P has been considered the most limiting nutrient in lowland tropical forests. In this study, scientists from Oak Ridge National Laboratory investigated the effects of P availability on carbon cycling in the Amazon region using a P-enabled land surface model. Model simulations demonstrate that CO2 fertilization effects in the Amazon region may be greatly overestimated if P cycling were not considered. Exploratory simulations highlighted the importance of considering the interactions between carbon, water, and nutrient cycling (both nitrogen and phosphorus) for the prediction of future carbon uptake in tropical ecosystems.

Contacts (BER PM)
Daniel Stover, Dorothy Koch and Renu Joseph
Daniel.Stover@science.doe.gov (301-903-0289)
dorothy.koch@science.doe.gov (301-903-0105)
renu.joseph@science.doe.gov (301-903-9237)

(PI Contact)
Xiaojuan Yang
Environmental Science Division and Climate Change Science Institute
Oak Ridge National Laboratory
yangx2@@ornl.gov (865-574-7615)

Funding
X. Yang, P.E. Thornton, D.M. Ricciuto, and F.M. Hoffman are supported by DOE Office of Science, Biological and Environmental Research, including support from the following programs: Regional and Global Climate Modeling Program (ORNL BGC-Feedbacks SFA), Terrestrial Ecosystem Science Program (ORNL TES SFA and NGEE-Tropics), Earth System Modeling (ACME project)  

Publications
Yang, X., P. E. Thornton, D. M. Ricciuto, and F. M. Hoffman. 2016. Phosphorus feedbacks constraining tropical ecosystem responses to changes in atmospheric CO2 and climate. Geophys. Res. Let. 43:7205-7214. doi:10.1002/2016GL069241. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 06, 2016

Enabling Remote Prediction of Leaf Age in Tropical Forest Canopies

Leaf spectral signatures can be used to predict leaf age across species, sites and canopy environments.

The Science
In tropical forests, knowing leaf age is a key component of understanding seasonal dynamics in carbon assimilation. However, a robust method for efficiently estimating leaf age across multiple species and environments did not exist. Here, we measured leaf age and leaf reflectance spectra and showed that our statistical model was able to predict leaf age across two contrasting forests in Peru and Brazil, and through diverse vertical gradients within the canopy.

The Impact
This study has three important implications for the broader plant science, remote sensing and modeling communities; (1) it shows that it is possible to monitor and map leaf age of tropical forest canopies and landscape using an imaging spectroscopy approach, (2) in combination with previous spectroscopy work that demonstrated the possibility of obtaining plant functional traits from leaf spectral signatures, this work highlights the possibility of using a spectroscopy approach to reconstruct temporal dynamics of leaf traits (i.e. morphological, physiological, and biochemical), (3) this work enables the retrieval of age dependent plant functional traits that can be used to parameterize new model structures in future terrestrial biosphere models.

Summary
Leaf age was estimated by tagging developing leaves at budburst and following their development with repeated in-situ photo documentations. We assembled 759 leaves from 11 tree species covering four canopy environments in an Amazonian evergreen forest in Brazil (August 2013-August 2014), including canopy sunlit leaves (red, n=4 trees), canopy shade leaves (yellow, n=4), mid- canopy leaves (green, n=3), and understory leaves (blue, n=4). Our results showed that a previously developed spectra-age model for Peruvian sunlit leaves also performed well for independent Brazilian sunlit and shade canopy leaves (R2 = 0.75-0.78), suggesting that canopy leaves  (and  their  associated  spectra)  follow constrained developmental  trajectories even in contrasting forests. The Peruvian model did not perform as well for Brazilian mid-canopy and understory leaves (R2 = 0.27-0.29), because leaves in different environments have distinct traits and trait developmental trajectories. When we accounted for distinct environment-trait linkages by re-parameterizing the spectra-only model to implicitly capture distinct trait-trajectories in different environments the resulting, more general, model was able to predict leaf age across diverse forests and canopy environments.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Lead author contact information            
Jin Wu
Brookhaven National Laboratory
jinwu@bnl.gov
   
Institutional contact
Alistair Rogers
Brookhaven National Laboratory
arogers@bnl.gov

Funding
J. Wu and SP. Serbin were supported in part by the Next-Generation Ecosystem Experiment (NGEE-Tropics) project. The NGEE-Tropics project is supported by the Office of Biological and Environmental Research in the Department of Energy, Office of Science.  

Publications
Wu J, Chavana-Bryant C, Prohaska N, Serbin SP, et al. (2016) Convergence in relationships between leaf traits, spectra and age across diverse canopy environments and two contrasting tropical forests. New Phytologist, 214:1033-1048 (2017). [DOI:10.1111/nph.14051]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Performance of leaf age models. From New Phytologist, 214:1033-1048 (2017).



June 27, 2016

Climate Study Finds Human Fingerprint in Northern Hemisphere

New analysis uses detection and attribution methods to establish multiyear trends of vegetation growth in northern-extratropical latitudes.

The Science
This study examines leaf area index (LAI; area of leaves per area of ground) during the growing season (April-October) over northern-extratropical latitudes (NEL; 30°-75°N). Previous work assessing modeled and observed LAI focused on timing of seasonal growth, interannual variability, and multiyear trends. These earlier studies showed that spatiotemporal changes in LAI were related to variation in climate drivers (mainly temperature and precipitation). This new study adds to an increasing body of evidence that NEL vegetation activity has been enhanced, as reflected by increased trends in vegetation indices, aboveground vegetation biomass, and terrestrial carbon fluxes during the satellite era. However, this analysis goes beyond previous studies by using formal detection and attribution methods to establish that the trend of increased northern vegetation greening is clearly distinguishable from both internal climate variability and the response to natural forcings alone. This greening can be rigorously attributed, with high statistical confidence, to anthropogenic forcings, particularly to rising atmospheric concentrations of greenhouse gases.

The Impact
This work demonstrates the first clear evidence of a discernible human fingerprint on NEL physiological vegetation changes and points to new investigations that could use detection and attribution methods to study broad-scale terrestrial ecosystem dynamics.

Summary
Significant NEL land greening has been documented through satellite observations during the past three decades. This enhanced vegetation growth has broad implications for surface energy, water, and carbon budgets, as well as ecosystem services across multiple scales. Discernable human impacts on Earth's climate system have been revealed by using statistical frameworks of detection and attribution. These impacts, however, were not previously identified on the NEL greening signal, due to the lack of long-term observational records, possible bias of satellite data, different algorithms used to calculate vegetation greenness, and lack of suitable simulations from coupled Earth system models (ESMs). Researchers, led by Oak Ridge National Laboratory, overcame these challenges to attribute recent changes in NEL vegetation activity. They used two 30-year-long, remote-sensing-based LAI datasets, simulations from 19 coupled ESMs with interactive vegetation, and a formal detection and attribution algorithm. Their findings reveal that the observed greening record is consistent with an assumption of anthropogenic forcings, where greenhouse gases play a dominant role, but is not consistent with simulations that include only natural forcings and internal climate variability. This evidence of historical, human-induced greening in the northern extratropics has implications for both intended and unintended consequences of human interactions with terrestrial ecosystems and the climate system.

Contacts (BER PM)
Renu Joseph
renu.joseph@science.doe.gov (301-903-9237)

Daniel Stover
Daniel.Stover@science.doe.gov (301-903-0289)

Jared DeForest
Jared.DeForest@science.doe.gov (301-903-1678)

PI Contact
Jiafu Mao
Environmental Sciences Division and Climate Change Science Institute
Oak Ridge National Laboratory (ORNL)
maoj@ornl.gov (865-576-7815)

Funding
Support for this work was provided by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research (BER), including support from the following BER programs: Regional and Global Climate Modeling [ORNL Biogeochemical-Feedbacks Scientific Focus Area (SFA)]; Terrestrial Ecosystem Science (ORNL TES SFA); Earth System Modeling (Accelerated Climate Modeling for Energy)

Publication
J. Mao, A. Ribes, B. Yan, X. Shi, P. E. Thornton, R. Séférian, P. Ciais, R. B. Myneni, H. Douville, S. Piao, Z. Zhu, R. E. Dickinson, Y. Dai, D. M. Ricciuto, M. Jin, F. M. Hoffman, B. Wang, M. Huang, and X. Lian, “Human-induced greening of the northern extratropical land surface.” Nature Climate Change 6(10), 959-63 (2016). [DOI: 10.1038/nclimate3056] (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Figure shows the spatial distribution of leaf area index trends (m2/m2/30 year) in the growing season (April-October) during the period of 1982-2011 in the mean of satellite observations (top), Earth system model (ESM) simulations with natural forcings alone (lower left), and ESM simulations with combined anthropogenic and natural forcings (lower right). [Image courtesy Oak Ridge National Laboratory]



June 27, 2016

Improving Predictions of Heterotrophic Respiration

Estimating heterotrophic respiration at large scales: challenges, approaches, and next steps.

The Science  
We proposed improving representation of heterotrophic respiration (HR) in Earth system models by grouping metabolism and flux characteristics across space and time.

The Impact
We argued for development of Decomposition Functional Types (DFTs), analogous to plant functional types (PFTs), for use in global models. We applied cluster analysis to produce example DFTs based on the global variability in 11 biotic and abiotic factors that influence decomposition processes.

Summary
Heterotrophic respiration (HR), the aerobic and anaerobic processes mineralizing organic matter, is a key carbon flux but one impossible to measure at scales significantly larger than small experimental plots. This impedes our ability to understand carbon and nutrient cycles, benchmark models, or reliably upscale point measurements. Given that a new generation of highly mechanistic, genomic-specific global models is not imminent, we suggest that a useful step to improve this situation is the development of Decomposition Functional Types (DFTs). Analogous to plant functional types (PFTs), DFTs would abstract and capture important differences in HR metabolism and flux dynamics, allowing modelers and experimentalists to efficiently group and vary these characteristics across space and time. We applied cluster analysis to show how annual HR can be broken into distinct groups associated with global variability in biotic and abiotic factors, and we demonstrated that these groups are distinct from, but complementary to, PFTs. In this position paper, we suggested priorities for next steps to build a foundation for DFTs in global models to provide the ecological and climate change communities with robust, scalable estimates of HR.

Contacts
Renu Joseph, Daniel Stover, SC-23.1
Renu.Joseph@science.doe.gov (301-903-9237), Daniel.Stover@science.doe.gov (301-903-0289)

Ben Bond-Lamberty (PNNL), Forrest M. Hoffman (ORNL), and Jitendra Kumar (ORNL)
bondlamberty@pnnl.gov, hoffmanfm@ornl.gov, and kumarj@ornl.gov

Funding
This research is the product of a working group on heterotrophic respiration led by M. Harmon and sponsored by the National Science Foundation, which funded meeting and travel expenses. B. Bond-Lamberty was supported by Office of Science of the U.S. Department of Energy as part of the Terrestrial Ecosystem Sciences Program. The Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830. R. Vargas and AD McGuire acknowledge support from the U.S. Department of Agriculture (2014-67003-22070) and U.S. Geological Survey, respectively. F.M. Hoffman and J. Kumar were supported by the Biogeochemistry-Climate Feedbacks (BGC Feedbacks) Scientific Focus Area and the Next Generation Ecosystem Experiments Tropics (NGEE-Tropics) Project, which are sponsored DOE Office of Science, BER, Regional & Global Climate Modeling and Terrestrial Ecosystem Science Programs in the Climate & Environmental Sciences Division. FMH and JK's contributions were authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy.

Publications
B. Bond-Lamberty, D. Epron, J. Harden, M. E. Harmon, F. M. Hoffman, J. Kumar, A. D. McGuire, and R. Vargas, "Estimating heterotrophic respiration at large scales: Challenges, approaches, and next steps." Ecosphere 7, (2016). doi:10.1002/ecs2.1380. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


June 13, 2016

Thawing Permafrost Could Accelerate Carbon Releases to the Atmosphere

These potential greenhouse gas emissions were found to be dominated by carbon dioxide, which has a lower global warming potential than methane.

The Science                       
Rapid warming in the Arctic is leading to the thawing of carbon-rich soils that have been permanently frozen for millennia. As these soils thaw, microbial decomposition could release greenhouse gases and increase the rate of global warming. A recent study looked at the potential amount of carbon that could be released into the atmosphere through this thawing and whether that carbon would be released as carbon dioxide or methane, a more potent greenhouse gas.

The Impact
The Arctic study found that the total amount of carbon released from thawing soils, and whether the carbon was released as carbon dioxide or methane, was related to whether soils were drier and aerobic or waterlogged and anaerobic. Total carbon release, even when taking into account the stronger warming potential of methane, was greatest under aerobic soil conditions, indicating that drier soils may provide a larger, positive feedback to global warming than wetter soils.  

Summary
An international research team led by Northern Arizona University used two meta-analyses to investigate the greenhouse gas release from soils sampled from across the permafrost zone and warmed in laboratory incubations. The first analysis focused on the amount of carbon released in response to warming, while the second analysis focused on the difference in the relative amount of carbon released as carbon dioxide or methane under aerobic or anaerobic soil conditions. Potential warming of 10°C increased total carbon release by a factor of two, and even when taking into account the stronger warming potential of methane, total carbon release was greatest under aerobic soil conditions. The implications of these results are that drier soils may provide a larger, positive feedback to global warming than wetter soils. Further studies are focused on addressing some of the key questions raised by this research. For example, where, when, and why will the Arctic become wetter or drier, and what are the implications for climate forcing? How should these processes be represented by mechanistic models of the Arctic?

PI Contact
Colleen M. Iversen
Senior Scientist
Climate Change Science Institute and
Environmental Sciences Division
Oak Ridge National Laboratory
One Bethel Valley Road, Bldg. 4500N
Oak Ridge TN 37831-6301
Phone: 865-241-3961
iversencm@ornl.gov

Contacts (BER PM)
Daniel Stover, SC-23.1, Daniel.Stover@science.doe.gov, 301-903-0289; and Jared DeForest, SC-23.1, Jared.DeForest@science.doe.gov, 301-903-1678

Funding
Financial support was provided by the National Science Foundation (NSF) Vulnerability of Permafrost Carbon Research Coordination Network grant 955713, with continued support from the NSF Research Synthesis and Knowledge Transfer in a Changing Arctic: Science Support for the Study of Environmental Arctic Change grant 1331083. Additional funding came from the Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program (DE-SC0006982); United Kingdom Natural Environment Research Council (NE/K000179/1); German Research Foundation (Excellence cluster CliSAP); Department of Ecosystem Biology, Grant agency of South Bohemian University, GAJU project numbers 146/2013/P and 146/2013/D; NSF Office of Polar Programs (1312402); NSF Division of Environmental Biology (0423385 and 1026843); European Union (FP-7-ENV-2011, project PAGE21, contract number 282700); Academy of Finland (project CryoN, decision number 132 045); Academy of Finland (project COUP, decision number 291691; part of the European Union Joint Programming Initiative, Climate); University of Eastern Finland (project FiWER); Maj and Tor Nessling Foundation; and Nordic Center of Excellence (project DeFROST).

Publication
Schädel, C., M. K. F. Bader, E. A. G. Schuur, C. Biasi, R. Bracho, P. Capek, S. De Baets, K. Diakova, J. Ernakovich, C. Estop-Aragones, D. E. Graham, I. P. Hartley, C. M. Iversen, E. Kane, C. Knoblauch, M. Lupascu, P. J. Martikainen, S. M. Natali, R. J. Norby, J. A. O'Donnell, T. R. Chowdhury, H. Santruckova, G. Shaver, V. L. Sloan, C. C. Treat, M. R. Turetsky, M. P. Waldrop, and K. P. Wickland. 2016. “Potential Carbon Emissions Dominated by Carbon Dioxide from Thawed Permafrost Soils,” Nature Climate Change, DOI: 10.1038/nclimate3054. (Reference link)

Related Links
NGEE Artic
Northern Arizona University news release
ORNL news release
University of Exeter news release
Michigan Tech news release

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



The coastal wetlands and polygonal landscapes on the North Slope of Alaska encompass a range of dry, aerobic tundra and wet, anaerobic tundra. [Image courtesy U.S. Department of Energy, Oak Ridge National Laboratory]



High-centered polygons in Barrow, Alaska, include dry, aerobic tundra surrounded by wet, anaerobic soils. [Image courtesy U.S. Department of Energy, Oak Ridge National Laboratory]



May 31, 2016

Microbial Protein Structure Altered when Exposed to Soil Mineral Surfaces

New findings may improve predictions using decomposition models and shed light on potential changes in protein activity.

The Science
The degradation of soil organic matter by microbes plays an important role in atmospheric carbon levels. A recent study examined how soil minerals could affect the stability of microbial proteins, potentially influencing the rate of carbon dioxide release into the atmosphere.

The Impact
The study shows that interactions with the surface of birnessite, but not other common soil minerals, have the potential to substantially alter the structure of bacterial proteins. These findings shed new light on how protein-mineral interactions could affect degradation rates of soil organic matter.

Summary
Soil contains the largest amount of terrestrial carbon on the planet, so a small change in soil carbon can have a large impact on atmospheric carbon dioxide levels. Therefore, understanding how organic carbon is released from soil into the atmosphere is a key question in climate science. Microbes produce enzymes that interact with soil minerals, and these protein-mineral interactions play an important role in the decomposition of soil organic carbon, which is subsequently released into the atmosphere. Not clear, however, is how different soil minerals affect the structure and function of microbial enzymes. To address this question, a team of researchers from the Department of Energy’s (DOE) Environmental Molecular Sciences Laboratory (EMSL), Oregon State University, and Leibniz Zentrum für Agrarlandschaftsforschung conducted molecular dynamics simulations to determine how interactions with surfaces of five common soil minerals affect the structure of a small bacterial protein called Gb1. The team performed simulations using the Cascade high-performance computer at EMSL, a DOE Office of Science user facility. The researchers found the Gb1 structure becomes highly altered due to interactions with Na+-birnessite mineral surfaces, but not kaolinite, montmorillonite, and goethite mineral surfaces. Interactions with birnessite caused the Gb1 protein structure to flatten and partially unravel. These findings shed light on how different soil minerals could affect the stability of microbial enzymes, thereby influencing the degradation rate of soil organic carbon. These insights build on previous, published experimental observations and could lead to more accurate projections of how much carbon dioxide could be released into the atmosphere as a result of microbial decomposition of soil organic matter.

BER PM Contact
Paul Bayer, SC-23.1, 301-903-5324

PI Contact
Amity Andersen
Environmental Molecular Sciences Laboratory
Pacific Northwest National Laboratory
amity.andersen@pnnl.gov

Funding
This work was supported by the Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science user facility; and the “Understanding Molecular-Scale Complexity and Interactions of Soil Organic Matter” Intramural Project at EMSL.

Publication
Andersen, A., P. N. Reardon, S. S. Chacon, N. P. Qafoku, N. M. Washton, and M. Kleber. 2016. “Protein-Mineral Interactions: Molecular Dynamics Simulations Capture Importance of Variations in Mineral Surface Composition and Structure,” Langmuir 32(24), 6194-209. DOI: 10.1021/acs.langmuir.6b01198. (Reference link)

Related Links
EMSL article: Microbial Protein's Structure can be Altered when Exposed to Soil Mineral Surfaces
EMSL article: Abiotic Pathway Makes Organic Nitrogen Compounds Available to Microbes and Plants

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 19, 2016

Variation in Stem Mortality Rates Determines Patterns of Above-Ground Biomass in Amazonian Forests: Implications for Dynamic Global Vegetation Models

Stem Mortality Controls Tropical Forest Biomass.

The Science             
Provides several key benchmarks for vegetation models in the Amazon basin via 1) spatial pattern maps of mortality, woody net primary productivity (NPP) and above-ground biomass (AGB), and 2) the underlying mechanisms controlling these patterns.

The Impact
Previous work had supposed that spatial patterns in AGB in Amazon forests were mediated by a positive association between woody NPP and stem mortality rates inducing reductions in AGB.  In contrast, we found that woody NPP and stem mortality are not correlated, and instead that spatial variability in AGB is controlled primarily by stem mortality (not woody biomass loss).

Summary
Understanding the processes that determine above-ground biomass (AGB) in Amazonian forests is important for predicting the sensitivity of these ecosystems to environmental change and for designing and evaluating dynamic global vegetation models (DGVMs). AGB is determined by inputs from woody net primary productivity (NPP) and the rate at which carbon is lost through tree mortality. Here, we test whether two direct metrics of tree mortality (the absolute rate of woody biomass loss and the rate of stem mortality) and/or woody NPP, control variation in AGB among 167 plots in intact forest across Amazonia. The observations show that stem mortality rates, rather than absolute rates of woody biomass loss, are the most important predictor of AGB, which is consistent with the importance of stand size structure for determining spatial variation in AGB. The relationship between stem mortality rates and AGB varies among different regions of Amazonia, indicating that variation in wood density and height/diameter relationships also influences AGB. In contrast to previous findings, we find that woody NPP is not correlated with stem mortality rates and is weakly positively correlated with AGB. The spatial pattern maps of mortality, net primary productivity and above-ground biomass (AGB), as well as the underlying mechanisms controlling these patterns provide key benchmark targets for DGVMs in Amazonia.

Contacts (BER PM)
Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

(PI Contact)
Brad Christoffersen
Los Alamos National Laboratory
bradley@lanl.gov, 505-665-9118 

Funding (DOE component in bold)
This paper is a product of the European Union's Seventh Framework Programme AMAZALERT project (282664). The field data used in this study have been generated by the RAINFOR network, which has been supported by a Gordon and Betty Moore Foundation grant, the European Union's Seventh Framework Programme projects 283080, ‘GEOCARBON'; and 282664, ‘AMAZALERT'; ERC grant ‘Tropical Forests in the Changing Earth System'), and Natural Environment Research Council (NERC) Urgency, Consortium and Standard Grants ‘AMAZONICA' (NE/F005806/1), ‘TROBIT' (NE/D005590/1) and ‘Niche Evolution of South American Trees' (NE/I028122/1). Additional data were included from the Tropical Ecology Assessment and Monitoring (TEAM) Network - a collaboration between Conservation International, the Missouri Botanical Garden, the Smithsonian Institution and the Wildlife Conservation Society, and partly funded by these institutions, the Gordon and Betty Moore Foundation, and other donors. Fieldwork was also partially supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico of Brazil (CNPq), project Programa de Pesquisas Ecológicas de Longa Duração (PELD-403725/2012-7). A.R. acknowledges funding from the Helmholtz Alliance ‘Remote Sensing and Earth System Dynamics'; L.P., M.P.C. E.A. and M.T. are partially funded by the EU FP7 project ‘ROBIN' (283093), with co-funding for E.A. from the Dutch Ministry of Economic Affairs (KB-14-003-030); B.C. was supported in part by the US DOE (BER) NGEE-Tropics project (subcontract to LANL). O.L.P. is supported by an ERC Advanced Grant and is a Royal Society-Wolfson Research Merit Award holder. P.M. acknowledges support from ARC grant FT110100457 and NERC grants NE/J011002/1, and T.R.B. acknowledges support from a Leverhulme Trust Research Fellowship.

Publications
Johnson, M. O. et al. Variation in stem mortality rates determines patterns of above-ground biomass in Amazonian forests: implications for dynamic global vegetation models. Global Change Biology 22, 3996-4013, 2016. DOI:10.1111/gcb.13315 . (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 18, 2016

Influences and Interactions of Inundation, Peat, and Snow on Active Layer Thickness

New study details active layer response across gradients of environmental conditions in Arctic permafrost.

The Science
Researchers used a physics-based numerical model validated at the Barrow (Alaska) Environmental Observatory to simulate the subsurface thermal hydrological response in permafrost tundra due to changing environmental conditions in organic soil layer thickness, snow depth, soil saturation, and ponded depth. 

The Impact
Researchers mapped the complex interaction of isolated environmental conditions that govern permafrost conditions. As a result, Arctic tundra response to changing conditions either by naturally occurring environmental gradients or by climate-induced perturbations can be inferred.

Summary
The collective work provides details on active layer thickness (ALT), or annual thaw depth above permafrost, related to three important environmental conditions characteristic of Arctic permafrost tundra: (1) organic soil layer thickness, (2) snow depth, and (3) unsaturated to inundated conditions. The work teases out how ALT will change as gradients along these environmental conditions are traversed in either space or time. One finding indicates that wetting or drying of polygonal tundra appears to have a minor effect on ALT compared to organic layer thickness and snow. At the same time, however, the inundation state is very interactive and can act to amplify other conditions that influence ALT; so much so, that subsurface thermal tipping points can be crossed. For example, the combined effect of inundation depth and snow can cause taliks, zone of year-round unfrozen soil, to form.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

(PI Contact)
Adam Atchley
Los Alamos National Laboratory
aatchley@lanl.gov; 505-665-6803

Funding
This work was supported by Los Alamos National Laboratory, Laboratory Direction Research and Development project LDRD201200068DR; and the Next-Generation Ecosystem Experiments (NGEE-Arctic) project, which is supported by the Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program.  

Publications
Atchley, A. L., E. T. Coon, S. L. Painter, D. R. Harp, and C. J. Wilson. 2016. “Influences and Interactions of Inundation, Peat, and Snow on Active Layer Thickness,” Geophysical Research Letters 43(10), 5116-23. DOI: 10.1002/2016GL068550. (Reference link)

Atchley, A. L., S. L. Painter, D. R. Harp, E. T. Coon, C. J. Wilson, A. K. Liljedahl, and V. E. Romanovskey. 2015. “Using Field Observations to Inform Thermal Hydrology Models of Permafrost Dynamics with ATS (v0.83),” Geoscientific Model Development 8, 2701-22. DOI: 10.5194/gmd-8-2701-2015. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 11, 2016

Shrubs Accelerate Wetland Water Loss

As shrubs encroach, their leaves drive the “wet” out of wetlands.

The Science
Water is a defining characteristic of wetlands and a key influence on biodiversity and biogeochemistry. Unfortunately, climate change and water management are making water a waning commodity in freshwater wetlands, facilitating the spread of woody shrubs into wetland sedge communities. Working in subtropical Florida peatlands, researchers found that the leaves of these shrub invaders use water less efficiently, resulting in increased loss of water to the atmosphere despite small increases in carbon uptake.

The Impact
Wetlands are critical for storage, filtration, and supply of freshwater. However, the dual impacts of human land use and climate drying due to warmer temperatures place these wetlands at risk, particularly in low-latitude regions where dense human populations are expanding. The feedback between external drying driving shrub encroachment and autogenic drying by those shrubs can degrade wetland habitat quality, biodiversity, and ecosystem function, compromising regional hydrology and carbon storage.

Summary
Studying sawgrass peatlands of south Florida, researchers from Florida Atlantic University quantified differences in plant photosynthetic efficiency and canopy structure between the historic dominant sedge and encroaching native willow to determine the degree to which vegetation carbon and water cycling is altered by shifts in community dominance. Leaf gas exchange of both carbon dioxide (plant photosynthetic uptake) and water (plant transpiration release) was greater for willow, which also used water less efficiently during photosynthesis (greater water loss per carbon gain). Additionally, the willow’s spreading, multitiered branch growth pattern produced more than double the leaf area index (leaf area per ground area). When scaled to the landscape, the elevated water loss rate and leaf density result in substantial increases in wetland water loss through transpiration with even small spatial extent of shrubs. Autogenic drying of wetlands may also accelerate litter and soil decomposition by increasing aerobic conditions, further compromising the health of these peatlands.  

Contacts (PI)
Brian Benscoter
Florida Atlantic University
Brian.Benscoter@fau.edu  
(BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program (DE-SC0008310), with site data and access provided by the St. Johns River Water Management District.

Publication
Budny, M. L., and B. W. Benscoter. 2016. “Shrub Encroachment Increases Transpiration Water Loss from a Subtropical Wetland,” Wetlands 36(4), 631-38. DOI: 10.1007/s13157-016-0772-5. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER



Field measurement of willow leaf gas exchange. [Image courtesy Michelle Budny, Florida Atlantic University]



Willow invading an herbaceous sawgrass community. [Image courtesy Brian Benscoter, Florida Atlantic University]



May 09, 2016

Model-Guided Field Experiments: Ecosystem CO2 Responses in an Australian Eucalypt Woodland

Multimodel a priori predictions for ecosystem CO2 responses in interaction with nutrient and water limitation.

The Science 
Quantitative model projections were made for the recently established Eucalyptus Free-Air CO2 Enrichment (EucFACE) experiment in Australia. Model simulations were designed to evaluate the experiment data as they are collected and to identify key measurements that should be made to discriminate among competing model assumptions.

The Impact
Knowledge of the causes of variation among models is now guiding data collection in the experiment, with the expectation that the guided experimental data collection will optimally inform future model improvements.

Summary
A major uncertainty in Earth system models is the response of terrestrial ecosystems to rising atmospheric carbon dioxide (CO2) concentration, particularly in nutrient-limited environments. The EucFACE experiment, established in a nutrient- and water-limited woodland, presents a unique opportunity to address uncertainty in Earth system models, but can best do so if key model uncertainties have been identified in advance. Researchers applied seven representative vegetation models to simulate a priori possible outcomes from EucFACE. Simulated responses to elevated CO2 of annual net primary productivity (NPP) ranged from 0.5% to 25% across models. The simulated NPP reduction during a low-rainfall year varied even more widely than the CO2 response—from 24% to 70%. Key processes where assumptions caused disagreement among models included nutrient limitations to growth, feedbacks to nutrient uptake, autotrophic respiration, and the impact of low soil moisture availability on plant processes.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

(PI Contact)
Anthony Walker
Environmental Sciences Division, Climate Change Science Institute
Oak Ridge National Laboratory
walkerap@ornl.gov

Funding
The National Climate Change Adaptation Research Facility (NCCARF) and Primary Industries Adaptation Research Network (PIARN) supported this project and travel for the participants to Sydney, Australia. Support was provided via EucFACE as an initiative supported by the Australian Government through the Education Investment Fund and the Department of Industry and Science, in partnership with the University of Western Sydney. Research support came from the Australian Research Council; U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research; and European Community's Seventh Framework Programme (FP7 2007-2013) under grant agreement 238366 (Greencycles II).

Publication
Medlyn, B. E., et al. 2016. “Using Models to Guide Field Experiments: A Priori Predictions for the CO2 Response of a Nutrient- and Water-Limited Native Eucalypt Woodland,” Global Change Biology 22, 2834-51. DOI: 10.1111/gcb.13268. (Reference link)

Related Link
Data

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 04, 2016

Permafrost Metaomics and Climate Change

A review of various molecular omics studies on permafrost microbial ecology under a changing climate.

The Science
Permanently frozen soil, or permafrost, covers a large portion of Earth’s terrestrial surface, and, as permafrost thaws, previously protected organic matter becomes available for microbial degradation. Microbes that decompose soil carbon produce carbon dioxide and other greenhouse gases, contributing substantially to climate change. A recent review summarizes the current information from various molecular omics studies on permafrost microbial ecology and explores the relevance of these insights to current understanding of the dynamics of permafrost loss due to climate change.

The Impact
Application of high-throughput sequencing and other omics technologies is enabling the study of permafrost microbial communities and providing high-resolution information about community composition and function in a variety of permafrost locations.

Summary
Permafrost is highly heterogeneous, and the impacts of thaw differ dramatically depending on geography, biochemistry, and microbial residents. A recent review summarizes the current state of knowledge about microbial ecology both within permafrost and in the soil layers activated as permafrost thaws, with an emphasis on the use of modern, high-throughput sequencing technologies to understand permafrost-associated microbial communities and their response to climate change. Understanding of the microbial mechanisms controlling greenhouse gas emissions is in its infancy. Metagenomics must be coupled with enhanced measurements of geochemistry and microbial processes to develop a comprehensive understanding of microbial function and activity in permafrost. Predictive understanding will require information generated by both laboratory-based experiments and long-term in situ studies. In the near future, it is imperative for knowledge generated by metagenomics and other omics approaches to be incorporated into climate models to fully integrate microbiology, geochemistry, geophysics, and hydrology for a better representation of Arctic ecosystems.

Contacts (BER PM)
Dan Stover (BER)
SC-23.1
daniel.stover@science.doe.gov; 301-903-0289

(PI Contact)
Neslihan Tas
Lawrence Berkeley National Laboratory
ntas@lbl.gov; 510-517-4035

Funding
This work was supported in part by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science (TES) program, under contract number DE-AC02-05CH11231. The authors acknowledge additional financial support from the Microbiomes in Transition (MinT) Initiative at Pacific Northwest National Laboratory, under contract number DE-AC05-76LO1803; DOE Next-Generation Ecosystem Experiment-Arctic (NGEE-Arctic) project; Danish Center for Permafrost (CENPERM); California State University Program for Education and Research in Biotechnology (CSUPERB) New Investigator Grant program; National Aeronautics and Space Administration Exobiology Program (award number NNX15AM12G), DOE Office of Biological and Environmental Research (award number DE-SC0004632); and University of Arizona Technology and Research Initiative Fund, through the Water, Environmental and Energy Solutions Initiative.

Publications
Mackelprang, R., S. R. Saleska, C. S. Jacobsen, J. K. Jansson, and N. Tas. 2016. “Permafrost Meta-Omics and Climate Change,” Annual Review of Earth and Planetary Sciences 44, 439-62. DOI: 10.1146/annurev-earth-060614-105126. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 20, 2016

Vast Underground Network of Fungi Detected from Space

Tree-mycorrhizal associations detected remotely from canopy spectral properties.

 The Science  
Researchers used satellite measurements of forest canopies to detect belowground fungal associations with trees across landscapes, testing the findings with 130,000 trees throughout the United States.

The Impact
Nearly all tree species associate with only one of two types of mycorrhizal fungi—arbuscular mycorrhizal (AM) fungi or ectomycorrhizal (ECM) fungi. AM- and ECM-dominated forests have distinct nutrient economies, so detection and mapping of these fungi can provide key insights into fundamental ecosystem properties.

Summary
Hidden belowground is a vast network of fungi that operates in a complex economy within forests, scavenging for nutrients and trading them to trees for carbon sugars. Researchers in a Department of Energy-supported study figured out how to detect this underground network from space. Understanding how different forests get their nutrients is critical to predicting how forests may grow—or be growth-stunted due to lack of nutrients—into the future. The type of mycorrhizal fungi is a key piece of that puzzle in determining how forests will respond to future changes in climate, carbon dioxide, water, and temperature. Scientists have known for many years which tree species associate with which fungi, but mapping every single tree species across large scales such as landscapes or continents has not been possible. The researchers used Landsat satellite measurements of forest canopies to detect mycorrhizal associations. They gathered data from 130,000 trees throughout the United States to test their approach, finding that they could predict 77% of the differences in mycorrhizal associations known on the ground from satellite observations alone.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

(PI Contact)
Joshua B. Fisher
University of California, Los Angeles; Jet Propulsion Laboratory
joshbfisher@gmail.com, 323-540-4569

Funding
Funding for the remote sensing analysis was provided by the U.S. Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program; National Science Foundation Ecosystem Science Program; and Indiana University.

Publications
Fisher, J. B., S. Sweeney, E. R. Brzostek, T. P. Evans, D. J. Johnson, J. A. Myers, N. A. Bourg, A. T. Wolf, R. W. Howe, and R. P. Phillips. 2016. “Tree-Mycorrhizal Associations Detected Remotely from Canopy Spectral Properties,” Global Change Biology 22(7), 2596-2607. DOI: 10.1111/gcb.13264. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 17, 2016

Assessing Earthquake-Induced Tree Mortality in Temperate Forest Ecosystems

A case study looks at the impact of earthquakes and forest dynamics in Wenchuan, China.

The Science
Earthquakes represent a significant driver to forest carbon dynamics. Using a newly developed approach for evaluating post-earthquake disturbance, this study estimates how much biomass carbon loss was associated with the 2008 Wenchuan earthquake in China.

The Impact
This study found that the committed forest biomass carbon loss associated with the May 12, 2008, Wenchuan earthquake (M=7.9) in China was 10.9 Tg C, with the highest tree mortality observed along the fault zone. These findings suggest that earthquake-induced biomass carbon loss should be included in estimating forest carbon budgets.

Summary
Earthquakes can produce significant tree mortality and consequently affect regional carbon dynamics. Unfortunately, detailed studies quantifying the influence of earthquakes on forest mortality are rare. This study assesses the committed forest biomass carbon loss associated with the 2008 Wenchuan earthquake in China with a synthetic approach that integrates field investigation, remote-sensing analysis, empirical models, and Monte Carlo simulations. The newly developed approach significantly improved the forest disturbance evaluation by quantitatively defining the earthquake impact boundary and detailed field survey to validate the mortality models. Based on this approach, a total biomass carbon of 10.9 Tg C was lost in the Wenchuan earthquake, which offset 0.23% of the living biomass carbon stock in Chinese forests. Tree mortality was highly clustered at the epicenter, declining rapidly with distance away from the fault zone. These findings suggest that earthquakes represent a significant driver to forest carbon dynamics, and the earthquake-induced biomass carbon loss should be included in estimating forest carbon budgets.

Contacts (BER PM)
Renu Joseph, SC-23.1, renu.joseph@science.doe.gov, 301-903-9237; and Daniel Stover, SC-23.1, daniel.stover@science.doe.gov, 301-903-0289

PI Contact
Robinson Negron-Juarez, robinson.inj@lbl.gov

Funding
This study was funded jointly by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA05050407) and the National Natural Science Foundation of China (41371126). Additional support came from the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Contract Number DE-AC02-05CH11231, as part of the Next-Generation Ecosystem Experiments–Tropics project and Regional and Global Climate Modeling program.

Publications
Zeng, H., et al. “Assessing earthquake-induced tree mortality in temperate forest ecosystems: A case study from Wenchuan, China.” Remote Sens. 8(3), 252 (2016). [DOI:10.3390/rs8030252]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 16, 2016

Accelerated Plant Metabolism May Not Speed Up Climate Change as Much as Anticipated

Plant respiration can acclimate to altered temperatures.

The Science  
A long-term study found that, over time, plants can adjust their metabolic rate to reduce the amount of carbon dioxide (CO2) returned to the atmosphere due to warming.

The Impact
Climate change impacts many aspects of Earth’s ecosystems, often in ways that can either slow or accelerate climate change. In a warming world, the return of CO2 to the atmosphere, via plant respiration, was expected to increase with temperature. This study found that plants growing in warmer conditions made adjustments that kept their metabolism on a stable trajectory, eliminating 80% of the possible “extra” carbon flux that would be released by nonacclimatized plants. If such responses are general, the acceleration of climate change by heightened plant respiration in a warmer world will be much smaller than anticipated by theory or Earth system models.

Summary
Plant respiration results in an annual CO2 flux to the atmosphere that is six times as large as that due to the emissions from fossil fuel burning, so changes in either will impact future climate. As plant respiration responds positively to temperature, a warming world may result in additional respiratory CO2 releases and, hence, further atmospheric warming. Plant respiration can acclimate to altered temperatures (e.g., by downward reduction of their entire temperature-response curve in warmer conditions), weakening the positive feedback of plant respiration to rising global air temperature. However, lack of evidence on long-term (weeks to years) acclimation to climate warming in field settings currently hinders realistic predictions of respiratory release of CO2 under future climatic conditions. To address this knowledge gap, a study was conducted from 2009 to 2013 to assess the acclimation capacity of more than 1,200 individuals of 10 dominant North American boreal and temperate tree species grown in ambient and warmed (+3.4 °C) plots in a unique open-air warming experiment in both open and understory forest habitats at two sites (~150 km apart) at the boreal-temperate forest ecotone in Minnesota, USA. For 1,620 leaves of these individuals, respiration was measured from 12 °C to 37 °C. Results found strong acclimation of leaf respiration to both experimental warming and seasonal temperature variation for juveniles of all 10 species. Plants grown and measured at temperatures 3.4 °C above ambient increased leaf respiration by 5% on average compared to plants grown and measured at ambient temperatures; without acclimation, these increases would have been 23%. Thus, acclimation eliminated 80% of the increase in leaf respiration expected of nonacclimated plants. Acclimation of leaf respiration per degree temperature change was similar for experimental warming and seasonal temperature variation. Moreover, the observed increase in leaf respiration per degree increase in temperature was less than half as large as the average reported for prior studies, which were conducted largely over shorter time scales in laboratory settings. If such dampening effects of leaf thermal acclimation occur generally, the increase of terrestrial plant respiration rates in response to climate warming may be less than predicted and, thus, may not raise atmospheric CO2 concentrations as much as anticipated.

Contacts (BER PM)
Daniel Stover, SC-23.1, daniel.stover@science.doe.gov, 301-903-0289; and Jared DeForest, SC-23.1, jared.deforest@science.doe.gov, 301-903-1678

(PI Contact)
Peter B. Reich
Department of Forest Resources, University of Minnesota
preich@umn.edu

Funding
This research was supported predominantly by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research award number: DE-FG02-07ER64456. Additional support was provided by the Minnesota Agricultural Experiment Station number: MIN-42-030 and number: MIN-42-060; Minnesota Department of Natural Resources; and College of Food, Agricultural, and Natural Resources Sciences and Wilderness Research Foundation, University of Minnesota.

Publications
Reich, P. B., et al. “Boreal and temperate trees show strong acclimation of respiration to warming.” Nature 531, 633–36 (2016). [DOI: 10.1038/nature17142]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 11, 2016

Predicting Biomass Of Hyperdiverse And Structurally Complex Central Amazonian Forests

Reliable biomass estimates require the inclusion of predictors that express inherent variations in species architecture.

The Science  
The hyperdiversity of tropical forests makes it difficult to predict their aboveground biomass levels based on biomass models that generalize across species. In a recent study, researchers employed a virtual forest approach using extensive field data to estimate biomass levels in the central Amazon.

The Impact
Due to the highly heterogenous nature of old-growth forests in structure and species composition, this study found that generic global or pantropical biomass estimation models can lead to strong biases.

Summary
Old-growth forests are subject to substantial changes in structure and species composition due to the intensification of human activities, gradual climate change, and extreme weather events. Trees store circa 90% of the total aboveground biomass (AGB) in tropical forests, and precise tree biomass estimation models are crucial for management and conservation. In the central Amazon, predicting AGB at large spatial scales is a challenging task due to the heterogeneity of successional stages, high tree species diversity, and inherent variations in tree allometry and architecture. The researchers parameterized generic AGB estimation models applicable across species and a wide range of structural and compositional variation related to species sorting into height layers as well as frequent natural disturbances. They used 727 trees from 101 genera and at least 135 species harvested in a contiguous forest near Manaus, Brazil. Sampling from this dataset, the researchers assembled six scenarios designed to span existing gradients in floristic composition and size distribution to select models that best predict AGB at the landscape level across successional gradients. They found that good individual tree model fits do not necessarily translate into reliable AGB predictions at the landscape level. Predicting biomass correctly at the landscape level in hyperdiverse and structurally complex tropical forests requires the inclusion of predictors that express inherent variations in species architecture. Reliable biomass assessments for the Amazon basin still depend on the collection of allometric data at the local and regional scales and forest inventories including species-specific attributes, which are often unavailable or estimated imprecisely in most regions.

Contacts (BER PM)
Renu Joseph, SC-23.1, renu.joseph@science.doe.gov, 301-903-9237; Daniel Stover, SC-23.1, daniel.stover@science.doe.gov, 301-903-0289

PI Contacts
Robinson Negron-Juarez, robinson.inj@lbl.gov
Jeffrey Q. Chambers, jchambers@lbl.gov

Funding
This study was financed by the Brazilian Council for Scientific and Technological Development (CNPq) within the projects Piculus, INCT Madeiras da Amazônia, and Succession after Windthrows (SAWI) (Chamada Universal MCTI/No 14/2012, Proc. 473357/2012-7), and supported by the Max Planck Institute for Biogeochemistry within the Tree Assimilation and Carbon Allocation Physiology Experiment (TACAPE). Further support was provided by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under contract number DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments–Tropics project and Regional and Global Climate Modeling program.

Publications
Magnabosco Marra, D., et al. “Predicting biomass of hyperdiverse and structurally complex central Amazonian forests: A virtual approach using extensive field data.” Biogeosciences 13, 1553–70 (2016). [DOI:10.5194/bg-13-1553-2016]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 02, 2016

Climate Change Affects How Soil Bacteria Breathe

A long-term experiment shows that climate shifts produce changes in soil bacteria functioning.

The Science
Understanding how climate change affects the way carbon cycles in and out of the soil is critical for predicting future changes in the carbon cycle, from ecosystem to global scales. This study capitalized on a long-term experiment in which mountain soils were transplanted between a hotter, drier lower elevation and a cooler, moist upper elevation to examine their response to climate change. The unprecedented 17-year length of this experiment is important because short-term experiments are not sufficient to adequately characterize all the ecosystem responses in slow-responding soils.

The Impact
Soils store an enormous amount of carbon globally, and arid land soils are considered particularly sensitive to the effects of climate change. Little is known, however, about how these soils might react as the climate changes, and long-term experiments are extremely rare. Because humans depend on soils for stabilizing carbon against greenhouse gas emissions, cropland production, and a wide variety of other ecosystem services, understanding the effects of climate change on soil is important. Climate change can alter soil physical structure, the composition of microbial communities that reside in soil, amount of carbon that soil can store, and the respiration response.

Summary
A research team, including Department of Energy (DOE) scientists at Pacific Northwest National Laboratory (PNNL), PNNL’s Joint Global Change Research Institute, and a U.S. Department of Agriculture researcher at Washington State University, transplanted soils between two elevations of semi-arid Rattlesnake Mountain, located in eastern Washington state. They chose sites separated by 500 m of elevation with similar plant species and soil types, but very different temperature and rainfall patterns. This experiment was initiated in 1994; 17 years later the team resampled the transplanted soils and controls, measuring carbon dioxide (CO2) production, temperature response, enzyme activity, and bacterial community structure. After incubating the soils for 100 days, they found that transplanted soils (i.e., soils that had been moved between the two sites in 1994) respired roughly equal cumulative amounts of carbon as the nontransplanted soils. Soils transplanted from the hot, dry lower site to the cooler, wetter upper site exhibited almost no respiratory response to temperature—as the temperature rose, they barely responded—but soils originally from the upper cooler site respired at higher rates. However, the bacterial community structure of transplants did not change. These findings show that the climate changes experienced by the transplanted soils prompted significant differences in microbial activity, but no observed change to bacterial structure. These results support the idea that environmental shifts can influence soil carbon through metabolic changes in the soil microbial population, and that those microbes, responsible for the soil-to-atmosphere CO2 flux, may be constrained in surprising ways.

Contacts (BER PM)
Daniel Stover, SC-23.1, daniel.stover@science.doe.gov, 301-903-0289; and Jared DeForest, SC-23.1, jared.deforest@science.doe.gov, 301-903-1678

(PI Contact)
Vanessa Bailey
Pacific Northwest National Laboratory
Vanessa.Bailey@pnnl.gov, 509-371-6965

Funding
This research was supported by DOE’s Office of Science, Office of Biological and Environmental Research (BER) as part of the Terrestrial Ecosystem Science program and the Signature Discovery Initiative at PNNL. Carbon analyses were performed at the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility sponsored by BER and located at PNNL.

Publication
Bond-Lamberty, B., et al. “Soil respiration and bacterial structure and function after 17 years of a reciprocal soil transplant experiment.” PLOS ONE 11(3), e0150599 (2015). [DOI:10.1371/journal.pone.0150599]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 26, 2016

Leaf Development and Demography Explain Photosynthetic Seasonality in Amazon Evergreen Forests

Cameras show how synchronized birth and death of leaves in the dry season drive increases in photosynthesis and reconcile ground- and satellite-based observations.

The Science  
Scientists used special tower-mounted cameras to discover that synchronization of leaf birth and death in evergreen forest trees across broad areas of the Brazilian Amazon is the cause of strong dry season increases in tropical forest photosynthesis. Furthermore, careful re-analysis of satellite data shows that, contrary to previous reports indicating that dry season increases in Amazon forest greenness may be an artifact of sun-sensor geometry problems, satellite observations do in fact show statistically significant dry-season greenup.

The Impact
These findings about how forests regulate their seasonal “breathing in” of atmospheric carbon dioxide help reconcile the seeming discrepancy between large seasonal changes in photosynthesis seen from towers on the ground versus the smaller changes in “greenness” seen from satellites in space. These findings will also help scientists better understand how climate influences these forests and more accurately predict how they will respond to future climate change.

Summary
In evergreen tropical forests, the extent, magnitude, and controls on photosynthetic seasonality are poorly resolved and inadequately represented in Earth system models. Combining camera observations with ecosystem carbon dioxide fluxes at forests across rainfall gradients in the Amazon, this work shows that aggregate canopy phenology, not seasonality of climate drivers, is the primary cause of photosynthetic seasonality in these forests. Specifically, synchronization of new leaf growth with dry season litterfall shifts canopy composition toward younger, more light-use efficient leaves, explaining large seasonal increases (~27%) in ecosystem photosynthesis. Coordinated leaf development and demography thus reconcile seemingly disparate observations at different scales and indicate that accounting for leaf-level phenology is critical for accurately simulating ecosystem-scale responses to climate change.

Contacts (BER PM)
Daniel Stover, SC-23/1, daniel.stover@science.doe.gov, 301-903-0289; and Jared DeForest, SC-23.1,
jared.deforest@science.doe.gov, 301-903-1678

(PI Contact)
Scott Saleska
Associate Professor, Ecology and Evolutionary Biology, University of Arizona
saleska@email.arizona.edu, 520-461-3330

Funding
Funding was provided by the National Science Foundation’s Partnerships for International Research and Education (0730305); National Aeronautics and Space Administration’s Terra-Aqua Science program (NNX11AH24G); and GOAmazon project, funded jointly by the U.S. Department of Energy (DE-SC0008383) and Brazilian state science foundations in Sao Paulo state (FAPESP) and Amazônas state (FAPEAM).

Publications
Wu, J., et al. “Leaf development and demography explain photosynthetic seasonality in Amazon evergreen forests.” Science 351, 972–76 (2016). [DOI: 10.1126/science.aad5068]. (Reference link)
Saleska, S. R., et al. “Dry–season greening of Amazon forests.” Nature 531, E4–E5 (2016). [DOI: 10.1038/nature16457]. (Reference link)

Related Links
www.saleskalab.org

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 26, 2016

Nitrogen Availability Increases in a Tundra Ecosystem During Experimental Permafrost Thaw

Plant access to an essential nutrient increases under warmed conditions.

The Science
Researchers warmed a tundra ecosystem in Alaska’s interior for 5 years with a novel experimental method. With this method, the researchers were able to warm the deep soil and degrade the permafrost, as well as document increases in plant access to soil nitrogen, a key nutrient.

The Impact
Global warming will result in the thaw of perennially frozen soils (permafrost), with releases of carbon to the atmosphere. However, this study’s findings show that increased growth of tundra plants could remove some of this carbon from the atmosphere, thus offsetting, in part, the accelerating feedback to climate change.

Summary
Researchers monitored nitrogen in tundra plants and soils during 5 years of experimental warming to quantify how plant access to soil nitrogen changed during permafrost thaw. Nitrogen is a scarce nutrient in high-latitude ecosystems, and plant access to soil nitrogen currently limits plant growth. Within 5 years of warming, plant-available nitrogen in soils increased. Warmed plants were able to grow larger and take up more carbon from the atmosphere than their unwarmed (control) neighbors. Though the study showed that plant biomass increased with warming, it is unlikely that the observed increase in plant carbon storage will be greater than losses of permafrost carbon at this site. In sum, plant carbon uptake offsets, in part, carbon releases from soils, but the system remains a net source of carbon to the atmosphere as a result of permafrost thaw and thus contributes toward accelerating climate change.

Contacts (BER PM)
Daniel Stover, SC-23.1, daniel.stover@science.doe.gov, 301-903-0289; and Jared DeForest, SC-23.1, jared.deforest@science.doe.gov, 301-903-1678

PI Contact
Edward A. G. Schuur
Center for Ecosystem Sciences and Society, Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011; Ted.Schuur@nau.edu

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program; National Science Foundation CAREER program; National Parks Inventory and Monitoring Program; National Science Foundation Bonanza Creek LTER program; National Science Foundation Office of Polar Programs; and a Discover Denali Research Fellowship awarded to V. Salmon.

Publications
Salmon, V. G., et al. “Nitrogen availability increases in a tundra ecosystem during 5 years of experimental permafrost thaw.” Glob. Change Biol. 22(5), 1927–41 (2015). [DOI:10.1111/gcb.13204]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 19, 2016

Capturing Detailed Dynamics of Tundra Polygonal Structures Using Statistical Modeling Methods

High-resolution predictions of land surface hydrological dynamics are desirable for improved investigations of regional- and watershed-scale processes. Direct deterministic simulations of fine-resolution land surface variables present many challenges, including high computational cost. In a recent Department of Energy (DOE)-supported study, statistically based reduced-order modeling techniques were used to facilitate emulation of fine-resolution simulations. An emulator, a Gaussian process regression, was used to approximate fine-resolution four-dimensional soil moisture fields predicted using a three-dimensional surface-subsurface hydrological simulator (PFLOTRAN). A dimension-reduction technique known as “proper orthogonal decomposition” is further used to improve the efficiency of the resulting reduced-order model (ROM). The ROM reduces simulation computational demand to negligible levels compared to the underlying fine-resolution model. In addition, the ROM constructed was equipped with an uncertainty estimate, allowing modelers to construct a ROM consistent with uncertainty in the measured data. The ROM is also capable of constructing statistically equivalent analogues that can be used in uncertainty and sensitivity analyses. The technique was applied to four polygonal tundra sites near Barrow, Alaska, that are part of DOE’s Next-Generation Ecosystem Experiments (NGEE)-Arctic project. The ROM is trained for each site using simulated soil moisture from 1998 to 2000 and validated using the simulated data for 2002 and 2006. The average relative root-mean-square errors of the ROMs are under 1 percent. The study shows that this statistical method successfully captures detailed physics in a computationally affordable way, and may be a suitable approach for modeling complex physical systems such as evolving tundra.

Reference: Liu, Y., G. Bisht, Z. M. Subin, W. J. Riley, and G. S. H. Pau. 2016. “A Hybrid Reduced-Order Model of Fine-Resolution Hydrologic Simulations at a Polygonal Tundra Site,” Vadose Zone Journal 15(2), DOI: 10.2136/vzj2015.05.0068. (Reference link)

Contact: Dorothy Koch, SC-23.1, (301) 903-0105, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 10, 2016

Data Synthesis in the Community Land Model for Ecosystem Simulation

An approach for extracting fundamental variables from simulated or observed ecosystem data and synthesizing other variables using the fundamental variables.

The Science  
Sampling theories, data-mining technologies, and virtual-sensor concepts were used to analyze the correlation between model parameters and bridge gaps between observation data streams and modeling data streams.

The Impact
It is an effort to use sampling theory, data-mining technologies, and virtual-sensor concepts to analyze the correlation between model parameters [e.g., over 60 parameters for the canopy flux module (temperature, air, ground, vegetation, carbon dioxide concentration, photosynthesis, leaf area index, and vcmax)] and to bridge the gaps between observation data streams and modeling data streams. This study is a key step forward in synthesizing model-required data streams from observation or measurable datasets, so that computational experiments can be constructed for direct model-data comparison.

Summary
This paper presents a data synthesis model to generate ecosystem data in climate simulations. This model is capable of (1) extracting key features of different physical properties in time and frequency domain, and (2) discovering and synthesizing the physical relationships between ecosystem variables in different feature spaces.

Contacts (BER PM)
Daniel Stover, SC-23.1, daniel.stover@science.doe.gov, 301-903-0289; Jared DeForest, SC-23.1, jared.deforest@science.energy.gov, 301-903-1678; and Dorothy Koch, SC-23.1, dorothy.koch@science.doe.gov, 301-903-0105.

(PI Contact)
Dali Wang
Environmental Science Division, Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN 37831
wangd@ornl.gov, 865-241-8679

Funding
The work was supported in part by NSFC grant 61305114, as well as the Terrestrial Ecosystem Science program and Accelerated Climate Modeling for Energy project funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. This work also used computing resources at Oak Ridge National Laboratory.

Publications
He, H., et al. “Data synthesis in the Community Land Model for ecosystem simulation.” J. Comput. Sci. 13, 83–95 (2016). [DOI:10.1016/j.jocs.2016.01.005]. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 06, 2016

Carbon Cost of Plant Nitrogen Acquisition

How is ecosystem growth and carbon sequestration limited by insufficient nitrogen?

The Science
Plants take up carbon from the atmosphere and use that carbon for growth, reproduction, and defenses. Researchers found that plants also use that carbon to acquire nitrogen from various sources—approximately 13 percent of useable carbon (net primary production or NPP) is used for nitrogen acquisition globally (2.4 Pg C yr-1).

The Impact
Most global terrestrial biosphere models do not include the carbon cost of nitrogen acquisition, thereby failing to represent nitrogen limitation to plant carbon dynamics. Much of the uncertainty in the modeled predictions of the future land carbon sink is driven by how these models prescribe nutrient constraints on primary production. Incorporation of these dynamics into global models will lead to improved changes in climate predictions.

Summary
A plant productivity-optimized nutrient acquisition model was integrated into one of the most widely used global terrestrial biosphere models, the Community Land Model (CLM). Global plant nitrogen uptake is dynamically simulated in the coupled model based on the carbon costs of nitrogen acquisition from mycorrhizal roots, non-mycorrhizal roots, symbiotic nitrogen-fixing microbes, and remobilization of nutrients from senescing leaves. Mycorrhizal uptake represented the dominant pathway by which nitrogen is acquired, accounting for about 66 percent of the nitrogen uptake by plants. Overall, the coupled model improves the representations of plant growth limitations globally. Such model improvements are critical for predicting how plant responses to altered nitrogen availability (from nitrogen deposition, rising atmospheric carbon dioxide, and warming temperatures) may impact the land carbon sink.

Contacts (BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

(PI Contact)
Joshua B. Fisher
University of California, Los Angeles; Jet Propulsion Laboratory
joshbfisher@gmail.com, 323-540-4569

Funding
Funding was provided by the U.S. Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Science Program; and the U.S. National Science Foundation’s Ecosystem Science Program.

Publications
Shi, M., J. B. Fisher, E. R. Brzostek, and R. P. Phillips. 2016. “Carbon Cost of Plant Nitrogen Acquisition: Global Carbon Cycle Impact from an Improved Plant Nitrogen Cycle in the Community Land Model,” Global Change Biology 22(3), 1299-1314. DOI: 10.1111/gcb.13131. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


December 22, 2015

Groundwater Increases Carbon Emissions from a Tropical Rainforest Stream

Discharges of old groundwater can greatly increase carbon dioxide emissions from streams and other surface waters.

The Science
Streams and rivers are increasingly recognized as an important component in the carbon cycle, from local to global scales. A recent study measured carbon dioxide (CO2) and methane (CH4) emissions from tropical rainforest streams in both the wet and dry seasons. Measurements were made in a stream receiving inputs of very old (about 3,000 years) groundwater and in other streams without such inputs.

The Impact
Measuring elevated stream CO2 degassing rates might suggest that an ecosystem has elevated respiration and is a net source (rather than sink) with respect to atmospheric CO2. In ecosystems with inputs of old, high-carbon groundwater, however, knowing that elevated stream CO2 degassing is supported and driven by a large input of nonbiogenic CO2 from old groundwater helps to avoid an overestimation of ecosystem respiration and provides a more accurate picture of the ecosystem’s carbon source and sink status.

Summary
CO2 and CH4 degassing was measured in two rainforest streams at La Selva, Costa Rica: one stream fed only by young (<10 years old) local groundwater recharged within the watershed, and another fed by about two-thirds young groundwater and one-third older groundwater (about 3,000 years old) from a large regional aquifer system. Regional groundwater inputs had no measurable effect on stream gas exchange velocity, stream water CH4 concentration, or stream CH4 emissions, but it significantly increased stream water CO2 concentration and degassing. CO2 emissions from the stream receiving regional groundwater averaged 5.5 moles of carbon per m2 of stream surface per day, about 7.5 times higher than the average from the stream with no regional groundwater input. Carbon emissions from both streams were dominated by CO2, with CH4 accounting for only 0.06 percent to 1.70 percent of the total (average CH4 degassing rate from both streams was 0.005 moles of carbon per m2 of stream surface per day). Annual stream degassing fluxes normalized by watershed area were 299 and 48 moles of carbon per m2 of watershed surface in the watersheds with and without inputs of old regional groundwater, respectively. Stream degassing of CO2 is a major carbon flux in the watershed receiving inputs of old regional groundwater, and is similar in magnitude to the average net ecosystem exchange estimated by eddy covariance. Examining the effects of watershed connections to underlying hydrogeological systems can help avoid overestimation of ecosystem respiration and advance understanding of the carbon source and sink status and overall carbon budgets of terrestrial ecosystems.

Contacts
(BER PM)

Daniel Stover, SC-23.1, daniel.stover@science.doe.gov, 301-903-0289; and Jared DeForest, SC-23.1, jared.deforest@science.doe.gov, 301-903-1678

(PI Contact)
David Genereux
North Carolina State University
genereux@ncsu.edu, 919-515-6017

Funding
This work was funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program (award DE-SC0006703).

Publications
Oviedo-Vargas, D., D. P. Genereux, D. Dierick, and S. F. Oberbauer. 2015. “The Effect of Regional Groundwater on Carbon Dioxide and Methane Emissions from a Lowland Rainforest Stream in Costa Rica,” Journal of Geophysical Research Biogeosciences 120(12), 2579–95. DOI: 10.1002/2015JG003009. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


December 11, 2015

Physiologically-Linked Indices of Rainfall Variation Predict Water Stress For Central U.S. Tree Species

Multiyear measurements enable researchers to predict impacts of precipitation regimes on central U.S. deciduous forest trees.

The Science
Long-term measurements at an AmeriFlux site in Missouri have enabled researchers to understand and predict how precipitation regimes affect water stress levels for key plant species in a central U.S. deciduous forest.

The Impact
How precipitation regimes affect water stress levels for plant species with contrasting water use strategies is not well understood. This study establishes a simple approach to quantifying plant physiological drought and the ecological impacts of precipitation regimes. This approach will be useful in predictions of forest response to climate change.

Summary
Variations in precipitation regimes can shift ecosystem structure and function by altering frequency, severity, and timing of plant water stress. Being able to predictively understand impacts of precipitation regimes on plant water stress is crucial in a changing climate. The research team, led by Oak Ridge National Laboratory (ORNL), formulated complementary, physiologically-linked indices of precipitation variability (PV) and related them to continuous measurements of predawn leaf water potential—a fundamental indicator of plant water status—in six tree species with different water use strategies in a central U.S. forest. These indices explained nearly all interannual variations in water stress levels for all species. These species differed in sensitivities to variations in precipitation regimes with the differences more pronounced in response to PV than to amount. Further, they exhibited stress tradeoffs between low and high PV, suggesting that how different plant species respond to PV is part of species-specific water use strategies in a plant community facing the uncertainty of fluctuating precipitation regimes. The new indices provide simple ways to quantify physiological drought and the ecological impacts of precipitation regimes in a changing climate.

Contacts
(BER PM)

Daniel Stover, SC-23.1, daniel.stover@science.doe.gov, 301-903-0289; and Jared DeForest, SC-23.1, jared.deforest@science.doe.gov, 301-903-1678

(PI Contact)
Lianhong Gu
Environmental Sciences Division and Climate Change Science Institute, ORNL
lianhong-gu@ornl.gov, 865-241-5925

Funding
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, Climate and Environmental Sciences Division. ORNL is managed by the University of Tennessee (UT)-Battelle, LLC, for DOE under contract DE-AC05-00OR22725.

Publications
Gu, L., S. G. Pallardy, K. P. Hosman, and Y. Sun. 2016. “Impacts of Precipitation Variability on Plant Species and Community Water Stress in a Temperate Deciduous Forest in the Central US,” Agricultural and Forest Meteorology 217, 120–36. DOI: 10.1016/j.agrformet.2015.11.014. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


December 07, 2015

Large Divergence of Satellite and Earth System Model Estimates of Global Terrestrial CO2 Fertilization

Atmospheric mass balance analyses suggest that terrestrial carbon storage is increasing, partially abating the atmospheric carbon dioxide (CO2) growth rate, although the continued strength of this ecosystem service remains uncertain. This research presents a new, satellite-derived global terrestrial Net Primary Production (NNP) dataset, which shows a significant increase in NPP from 1982 to 2011. However, comparison against Earth system model (ESM) estimates reveals a significant divergence, with satellite-derived increases (2.8 ± 1.5%) less than half of ESM-derived increases (7.60 ± 1.67%) over the 30-year period. By isolating the CO2 fertilization effect and comparing against a synthesis of available free-air CO2 enrichment data, the researchers provide evidence that much of the discrepancy may be due to an over-sensitivity of ESMs to atmospheric CO2, potentially reflecting an under-representation of climatic feedbacks and a lack of representation of nutrient constraints. Understanding of CO2 fertilization effects on NPP needs rapid improvement to enable more accurate projections of future carbon cycle-climate feedbacks. The study suggests that better integration of modeling, satellite, and experimental approaches offers a promising way forward.

Reference: Smith, W. K., S. C. Reed, C. C. Cleveland, A. P. Ballantyne,W. R. L. Anderegg, W. R.Wieder, Y. Y. Liu, and S. W. Running. 2015 “Large Divergence of Satellite and Earth System Model Estimates of Global Terrestrial CO2 Fertilization,” Nature Climate Change 6, 306-10. DOI: 10.1038/nclimate2879. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 26, 2015

Warming Increases Carbon Losses in Biocrust Soils

Many arid and semiarid ecosystems have soils covered with well-developed biological soil crust communities (biocrusts) made up of mosses, lichens, cyanobacteria, and heterotrophs living at the soil surface. These communities are a fundamental component of dryland ecosystems and are critical to dryland carbon cycling. To examine the effects of warming temperatures on soil carbon balance in a dryland ecosystem, a recent study used infrared heaters to warm biocrust-dominated soils to 2°C above control conditions at a field site on the Colorado Plateau. The researchers monitored net soil exchange (NSE) of carbon dioxide (CO2) every hour for 21 months using automated flux chambers (5 control and 5 warmed chambers), which included the CO2 fluxes of the biocrusts and the soil beneath them. They observed measurable photosynthesis in biocrust soils on 12 percent of measurement days, which correlated well with precipitation events and soil wet-up. These days included several snow events, providing what is believed to be the first evidence of substantial photosynthesis underneath snow by biocrust organisms in drylands. Overall, biocrust soils in both the control and warmed plots were net CO2 sources to the atmosphere, with control plots losing 62 ± 8 g carbon m-2 (mean ± SE) over the first year of measurement and warmed plots losing 74 ± 9 g carbon m-2. Between the control and warmed plots, the difference in soil carbon loss was uncertain over the course of the entire year due to large and variable rates in spring, but on days during which soils were wet and crusts were actively photosynthesizing, biocrusts that were warmed by 2 oC had a substantially more negative carbon balance (i.e., biocrust soils took up less carbon and/or lost more carbon in warmed plots). Taken together, these data suggest a substantial risk of increased carbon loss from biocrust soils with higher future temperatures, and highlight a robust capacity to predict CO2 exchange in biocrust soils using easily measured environmental parameters.

Reference: Darrouzet-Nardi, A., S. C. Reed, E. E. Grote, and J. Belnap. 2015. “Observations of Net Soil Exchange of CO2 in a Dryland Show Experimental Warming Increases Carbon Losses in Biocrust Soils,” Biogeochemistry 126, 366-78. DOI: 10.1007/s10533-015-0163-7. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 23, 2015

Geochemical Analysis of Permafrost Soils Reveals Factors Controlling Methane Emissions from Arctic Tundra

A recent study measured the changes in dissolved organic carbon compounds during anoxic incubations of low-centered polygon soils from the Barrow Environmental Observatory in Alaska (Herndon et al. 2015a). Analyses used Fourier transform infrared and ultraviolet-visible spectroscopies to identify an initial increase in soluble carbohydrate and organic acid pools, followed by a decline in organic acids. These results describe the upstream microbial processes of soil organic matter decomposition that feed anaerobic microbial fermentation, methanogenesis, and iron reduction, which are highly temperature-sensitive processes and thus likely to control rate and magnitude of methane emissions from thawing permafrost. In a companion study, samples from mineral and organic soils were analyzed at the Stanford Synchrotron Radiation Lightsource to further characterize the geochemistry of active layer soils and permafrost (Herndon et al. 2015b). From those results, the researchers infer that geochemical differences induced by water saturation dictate microbial products of soil organic matter decomposition, and that iron geochemistry is an important factor regulating methanogenesis in anoxic tundra soils. Together, these coordinated datasets provided a conceptual framework from which to parameterize and enhance fine-scale biogeochemical models from the Next-Generation Ecosystem Experiments-Arctic project that specifically represent these anaerobic processes. The datasets are being used to assess the effects of newly represented iron-reduction processes on simulations of carbon dioxide, methane, and pH production in one-dimensional models.

References:
Herndon, E. M., B. F. Mann, T. R. Chowdhury, Z. Yang, D. E. Graham, S. D. Wullschleger, L. Liang, and B. Gu. 2015a. “Pathways of Anaerobic Organic Matter Decomposition in Tundra Soils from Barrow, Alaska,” Journal of Geophysical Research Biogeosciences 120, 2345-59. DOI: 10.1002/2015JG003147. (Reference link)

Herndon, E. M., Z. Yang, J. Bargar, N. Janot, T. Z. Regier, D. E. Graham, S. D. Wullschleger, B. Gu, and L. Liang. 2015b. “Geochemical Drivers of Organic Matter Decomposition in the Active Layer of Arctic Tundra Soils,” Biogeochemistry 126(3), 397-414. DOI: 10.1007/s10533-015-0165-5. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 18, 2015

Elevated CO2 Levels Alter Forest Succession and Carbon Cycling

Regenerating forests influence the global carbon cycle, and understanding how climate change will affect patterns of regeneration and carbon storage is necessary to predict the rate of atmospheric carbon dioxide (CO2) increase in future decades. While experimental CO2 elevation has revealed that young forests respond with increased productivity, there remains considerable uncertainty as to how the long-term dynamics of forest regrowth are shaped by elevated CO2 (eCO2). In a recent study, researchers used the mechanistic size- and age-structured Ecosystem Demography model to investigate the effects of CO2 enrichment on forest regeneration, using data from the Duke Forest Free-Air Carbon Dioxide Enrichment (FACE) experiment, a forest, and an eddy-covariance tower for model parameterization and evaluation. They found that the dynamics of forest regeneration are accelerated, and stands consistently hit a variety of developmental benchmarks earlier under eCO2. Because responses to eCO2 varied by plant functional type, successional pathways and mature forest composition differed under eCO2, with mid- and late-successional hardwood functional types experiencing greater increases in biomass compared to early-successional functional types and the pine canopy. Over the simulation period, eCO2 led to an increase in total ecosystem carbon storage of 9.7 Mg carbon/ha. Model predictions of mature forest biomass and ecosystem-atmosphere exchange of CO2 and water were sensitive to assumptions about nitrogen limitation; both the magnitude and persistence of the ecosystem response to eCO2 were reduced under nitrogen limitation. These simulations demonstrate that eCO2 can result in a general acceleration of forest regeneration, while altering the course of successional change and having a lasting impact on forest ecosystems.

Reference: Miller, A. D., M. C. Dietze, E. H. DeLucia, and K. J. Anderson-Teixeira. 20156. “Alteration of Forest Succession and Carbon Cycling Under Elevated CO2,” Global Change Biology 22(1), 351-63. DOI: 10.1111/gcb.13077. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 12, 2015

Representing Northern Peatland Microtopography and Hydrology Within the Community Land Model

Predictive understanding of northern peatland hydrology is a necessary precursor to understanding the fate of massive carbon stores in these systems under the influence of present and future climate change. Current models have begun to address microtopographic controls on peatland hydrology, but none have included a prognostic calculation of peatland water table depth for a vegetated wetland, independent of prescribed regional water tables. A recent study introduces a new configuration of the Community Land Model (CLM), which includes a fully prognostic water table calculation for a vegetated peatland. The structural and process changes to CLM focus on modifications needed to represent the hydrologic cycle of the bog environment with perched water tables, as well as distinct hydrologic dynamics and vegetation communities of the raised hummock and sunken hollow microtopography characteristic of peatland bogs. The modified model was parameterized and independently evaluated against observations from an ombrotrophic raised-dome bog in northern Minnesota (S1-Bog), the site for the Spruce and Peatland Responses Under Climatic and Environmental Change experiment (SPRUCE). Simulated water table levels compared well with site-level observations. The new model predicts hydrologic changes in response to planned warming at the SPRUCE site. At present, standing water is commonly observed in bog hollows after large rainfall events during the growing season, but simulations suggest a sharp decrease in water table levels due to increased evapotranspiration under the most extreme warming level, nearly eliminating the occurrence of standing water in the growing season. Simulated soil energy balance was strongly influenced by reduced winter snowpack under warming simulations, with the warming influence on soil temperature partly offset by the loss of insulating snowpack in early and late winter. The new model provides improved predictive capacity for seasonal hydrological dynamics in northern peatlands and a useful foundation for investigating northern peatland carbon exchange.

Reference: Shi, X., P. E. Thornton, D. M. Ricciuto, P. J. Hanson, J. Mao, S. D. Sebestyen, N. A. Griffiths, and G. Bisht. 2015. “Representing Northern Peatland Microtopography and Hydrology Within the Community Land Model,” Biogeosciences 12(21), 6463–77. DOI: 10.5194/bg-12-6463-2015. (Reference link)

Contact: Dorothy Koch, SC-23.1, (301) 903-0105, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 09, 2015

Comprehensive Data Acquisition and Management System for Ecosystem-Scale Warming and Elevated CO2 Experiment

Ecosystem-scale manipulation experiments represent large science investments that require well-designed data acquisition and management systems to provide reliable, accurate information to project participants and third party users. The Spruce and Peatland Responses Under Climatic and Environmental Change (SPRUCE) project is such an experiment funded by the Department of Energy’s Terrestrial Ecosystem Science program. The SPRUCE experimental mission is to assess ecosystem-level biological responses of vulnerable, high-carbon terrestrial ecosystems to a range of climate warming manipulations and an elevated carbon dioxide (CO2) atmosphere. SPRUCE provides a platform for testing mechanisms controlling the vulnerability of organisms, biogeochemical processes, and ecosystems to climatic change (e.g., thresholds for organism decline or mortality, limitations to regeneration, biogeochemical limitations to productivity, and cycling and release of CO2 and methane to the atmosphere). As a result, the SPRUCE experiment will generate a wide range of continuous and discrete measurements. In a recent publication, project researchers lay out their approach to meeting the challenges of designing and constructing an efficient data system for managing high volume sources of in situ observations in a remote and harsh environmental location. The approach covers data flow starting from the sensors and ending at the archival and distribution points, discusses types of hardware and software used, examines design considerations that were used to choose them, and describes the data management practices chosen to control and enhance the data’s value.

Reference:Krassovski, M. B., J. S. Riggs, L. A. Hook, W. R. Nettles, P. J. Hanson, and T. A. Boden. 2015. “A Comprehensive Data Acquisition and Management System for an Ecosystem-Scale Peatland Warming and Elevated CO2 Experiment,” Geoscientific Instrumentation, Methods, and Data Systems 4, 203–13. DOI: 10.5194/gi-4-203-2015. (Reference link)
See also SPRUCE project website at http://mnspruce.ornl.gov.

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 02, 2015

Toward Improved Model structures for Analyzing Priming Effect

Rising atmospheric carbon dioxide (CO2) concentrations are projected to increase plant inputs to soil, which may stimulate soil carbon decomposition. Many studies attempting to quantify this priming effect use a simple analytical framework that is inappropriate for inferring complex dynamics. Using a multipool soil carbon model, a recent study shows that changes in carbon flows that would be attributed to priming in a one-pool model (using overall respiration and carbon stocks) can be explained without a change in decomposition rate constants of individual pools. Furthermore, a sensitivity analysis demonstrates the potential range of “false priming” responses inferred from simple, first-order models. The researchers argue that, in addition to standard measurements of carbon stocks and CO2 fluxes, quantifying the fate of new plant inputs requires isotopic tracers and microbial measurements. They discuss the pitfalls of using simple model structures to infer complex dynamics and suggest appropriate model structures and necessary observational constraints for projections of carbon feedbacks.

Reference: Georgiou, K., C. D. Koven, W. J. Riley, and M. S. Torn. 2015. “Toward Improved Model Structures for Analyzing Priming: Potential Pitfalls of Using Bulk Turnover Time,” Global Change Biology 21(12), 4298–4302. DOI:10.1111/gcb.13039. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 17, 2015

Vertical Transport of Greenhouse Gases Through the Nocturnal Atmospheric Boundary Layer

Results from a tracer release study were applied to estimate a tower footprint.

The Science
At night, can an upper-level carbon dioxide sensor be overly influenced by gas released from nearby vegetation, reducing researchers’ confidence in its ability to provide information on continental-scale surface fluxes? The vertical dispersion of a gas released at night was studied with a field project in South Carolina comprising (1) the release of five perfluorocarbons (inert airborne “tracer” gases) from multiple surface locations, and (2) downwind detection of the tracers at four elevations on a tall television transmitter tower.

The Impact
A simulation of the tracer release reproduced the motion of tracer from its source to the detectors, but also indicated that the uppermost detector (at 329 m above ground) was mainly sampling air from far beyond 25 km, with a minor contribution from areas within that range. Therefore, for nocturnal conditions, the researchers are confident that the tower is sampling air from over a regional-scale area (25 km to 150 km), and is only weakly influenced by nearby emissions.

Summary
On two nights characterized by moderate to strong vertical stability, tracer gases were released at the surface from locations upwind of a South Carolina tower equipped with sensors at 34 m, 68 m, and 329 m. The uppermost sensor was able to detect the tracer gas released from the ground at a distance of about 25 km—evidence for some vertical transport despite the weak vertical mixing on the nights it was released. Simulations of the experiment, validated against the field project data, were conducted to estimate the tower “footprint,” or total area from which tracer released at the surface will be detected by the 329 m sensor. These simulations indicate that most of the air reaching the highest tower level came from surface locations much more distant than the domain of the tracer release, with the sensor footprint extending well beyond 25 km. The low-level nocturnal jet (located at 100 m to 1000 m above ground, and at 8-20 m/sec speed) was an important reason for the dominant role of distant upwind sources.

Contact (BER PM)
Dan Stover
SC-23.1
daniel.stover@science.doe.gov, 301-903-0289

(PI Contact)
David Werth
Savannah River National Laboratory
David.Werth@srnl.doe.gov, 803-725-3717

Funding
Funding was provided by the U.S Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program.

Publication
Werth, D., R. Buckley, G. Zhang, R. Kurzeja, M. Leclerc, H. Duarte, M. Parker, and T. Watson. 2015. “Quantifying the Local Influence at a Tall Tower Site in Nocturnal Conditions,”Theoretical and Applied Climatology, DOI:10.1007/s00704-015-1648-y. (Reference link)

Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 29, 2015

Climate Change and Physical Disturbance Cause Similar Community Shifts in Biological Soil Crusts

Biological soil crusts (biocrusts)—communities of mosses, lichens, cyanobacteria, and heterotrophs living at the soil surface—are fundamental components of drylands worldwide, and their destruction dramatically alters biogeochemical processes, hydrology, surface energy balance, and vegetation cover. Impacts of physical disturbances on biocrusts (e.g., trampling by livestock and damage from vehicles) have been a long-standing concern, and concern is also increasing over the potential for climate change to alter biocrust community structure. Using long-term data from the Colorado Plateau, a recent study examined the effects of 10 years of experimental warming and altered precipitation on biocrust communities and compared the effects of altered climate with those of long-term physical disturbance (more than 10 years of replicated human trampling). Surprisingly, altered climate and physical disturbance treatments had similar effects on biocrust community structure. Warming, altered precipitation, and physical disturbance from trampling all promoted early successional community states. Although the pace of biocrust community change varied significantly among treatments, these results suggest that multiple aspects of climate change will affect biocrusts to the same degree as physical disturbance. This finding is particularly disconcerting in the context of warming, as temperatures for drylands are projected to increase beyond those imposed as treatments in this study.

Reference: Ferrenberg, S., S. C. Reed, and J. Belnap. 2015. “Climate Change and Physical Disturbance Cause Similar Community Shifts in Biological Soil Crust,” Proceedings of the National Academy of Sciences (USA) 112(39), 12116-121. DOI: 10.1073/pnas.1509150112. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 15, 2015

Fog and Rain in the Amazon

The diurnal and seasonal water cycles in the Amazon remain poorly simulated in general circulation models. Simulations using existing models exhibit peak evapotranspiration during the wrong season and rain occurring too early in the day. A team of researchers supported by the Terrestrial Ecosystem Science and Atmospheric System Research programs and using data from the GOAmazon campaign show that those biases are not present in an approach opposite to that taken by general circulation models, in which they resolve convection and parameterize large-scale circulation as a function of the resolved convection.

The ability to simulate the seasonality of the hydrologic cycle in the Amazon using this approach is attributed to (1) the representation of the morning fog layer, and (2) more accurate characterization of convection and its coupling with large-scale circulation. The morning fog layer, present during the wet season, but absent in the dry season, dramatically increases cloud albedo, which reduces evapotranspiration through its modulation of the surface energy budget. These results highlight the importance of the coupling between the energy and hydrological cycles and the key role of cloud albedo feedback for climates over tropical continents. The study indicates understanding of tropical climates over land can be considerably advanced by using coupled land–atmosphere models with explicit convection and parameterized large-scale dynamics.

Reference: Anber, U., P. Gentine, S. Wang, and A. H. Sobel. 2015. “Fog and Rain in the Amazon,” Proceedings of the National Academy of Sciences (USA) 112(37), 11,473–477. DOI: 10.1073/pnas.1505077112. (Reference link)

Contact: Sally McFarlane, SC-23.1, (301) 903-0943, Daniel Stover, SC-23.1, (301) 903-0289, Ashley Williamson, SC-23.1, (301) 903-3120
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 02, 2015

Links Between Ecosystem Multifunctionality and Above- and Belowground Biodiversity Mediated by Climate

Plant biodiversity is often correlated with ecosystem functioning in terrestrial ecosystems. However, little is known about the relative and combined effects of above- and belowground biodiversity on multiple ecosystem functions [e.g., ecosystem multifunctionality (EMF)] or how climate might mediate those relationships. A recent study teases apart the effects of biotic and abiotic factors, both above- and belowground, on EMF on the Tibetan Plateau in China. The researchers found that a suite of biotic and abiotic variables account for up to 86% of the EMF variation, with the combined effects of above- and belowground biodiversity accounting for 45% of the EMF variation. These results have two important implications: (1) including belowground biodiversity in models can improve the ability to explain and predict EMF, and (2) regional-scale variation in climate, and perhaps climate change, can determine, or at least modify, the effects of biodiversity on EMF in natural ecosystems.

Reference: Jing, X., N. J. Sanders, Y. Shi, H. Chu, A. T. Classen, K. Zhao, L. Chen, Y. Shi, Y. Jiang, and J.-S. He. 2015. “The Links Between Ecosystem Multifunctionality and Above- and Belowground Biodiversity are Mediated by Climate,” Nature Communications 6(8159), DOI: 10.1038/ncomms9159. (Reference link)

Media:

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 24, 2015

Call for Expansion of International Soil Experiment Networks

Researchers are calling for an expansion of international networks of deep soil manipulation experiments in the field, with coordination, common variables, integration, and collaboration. Siting along environmental and land-use gradients will accelerate understanding of soil organic carbon (SOC) cycling. Data are lacking to unravel the importance of various mechanisms controlling deep SOC cycling in different soils under different environmental conditions. Field manipulation experiments will overcome limitations of laboratory studies, enabling testing for cause and effect and isolating direct response function in real ecosystems. Reduced uncertainty of the role of soils as positive or negative feedbacks to global climate change will improve climate projections. Also, mitigation strategies and solutions for ecological and agricultural challenges can be developed and tested at the networks’ facilities.

Reference: Torn, M. S., A. Chabbi, P. Crill, P. J. Hanson, I. A. Janssens, Y. Luo, C. H. Pries, C. Rumpel, M. W. I. Schmidt, J. Six, M. Schrumpf, and B. Zhu. 2015. “A Call for International Soil Experiment Networks for Studying, Predicting, and Managing Global Change Impacts,” SOIL 1, 575–82. DOI:10.5194/soil-1-575-2015. (Reference link)

Contact: Daniel Stover, SC-23.1, (301) 903-0289, Jared DeForest, SC-23, (301) 903-3251
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 28, 2015

Foliar Age and Season Affect Photosynthetic Temperature Response in Black Spruce

Black spruce trees at the southern edge of the vast boreal forest are being exposed to progressive increases in temperature due to climate change. Temperature increases could change the balance between photosynthetic uptake of carbon dioxide (CO2) and respiratory release of CO2, which could further affect climate change. Since black spruce trees retain their needles for several years, the different age classes may have different responses to temperature increases. Thus, to understand and model how the boreal forest will function in the future, seasonal- and age-specific photosynthetic and respiratory temperature response functions must be measured. From 2011 to 2014, research was undertaken in a nutrient-limited black spruce and Sphagnum bog forest in northern Minnesota in the United States. Measurements were collected seasonally on different needle age classes from mature trees and included photosynthetic capacity, foliar respiration (Rd), and leaf biochemistry. Scientists from Oak Ridge National Laboratory used the results to model the predicted total annual carbon uptake by the trees under normal and elevated temperature scenarios. Temperature responses of key photosynthetic parameters were dependent on season and less responsive in the developing new needles (Y0) as compared with 1-year-old (Y1) or 2-year-old (Y2) needles. Each process initially increased with temperature, peaking between 19 °C and 38 °C, then declined at higher temperatures. Different age classes differed in their leaf structure and photosynthetic capacity, which resulted in 64% of modeled total annual carbon uptake from the older Y1 and Y2 needles (56% of the tree leaf area), and just 36% from Y0 cohorts (44% of tree leaf area). Under warmer climate change scenarios, the contribution of young needles was even less, just 31% of annual carbon uptake for a modeled 9 °C rise in summer temperature. Results suggest that net annual carbon uptake by black spruce could increase under elevated temperature and become more dependent on the older needle age classes. This study illustrates the physiological and ecological significance of different leaf ages, and indicates the need for seasonal- and leaf age-specific model parameterization when estimating carbon uptake capacity of boreal forests under current or future temperatures.

Reference: Jensen, A. M., J. M. Warren, P. J. Hanson, J. Childs, and S. D. Wullschleger. 2015. “Needle Age and Season Influence Photosynthetic Temperature Response in Mature Picea mariana Trees,” Annals of Botany 116, 821–32. DOI: 10.1093/aob/mcv115. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 04, 2015

Sustained Carbon Uptake and Storage Following Moderate Disturbance in a Great Lakes Forest

Carbon uptake rates in many forests are sustained, or decline only briefly, following disturbances that partially defoliate the canopy. The mechanisms supporting such functional resistance to moderate forest disturbance are largely unknown. Researchers used a large-scale experiment to identify mechanisms sustaining carbon uptake through partial canopy defoliation. The Forest Accelerated Succession Experiment in northern Michigan employs a suite of carbon-cycling measurements within paired treatment and control meteorological flux tower footprints. They found that enhancement of canopy light-use efficiency and maintenance of light absorption maintained net ecosystem production and aboveground wood net primary production (NPP) when leaf-area index (LAI) of the treatment forest temporarily declined by nearly half its maximum value. In the year following peak defoliation, redistribution of nitrogen in the treatment forest from senescent early successional aspen and birch to nongirdled later successional species facilitated the recovery of total LAI to predisturbance levels. Sustained canopy physiological competency following disturbance coincided with a downward shift in maximum canopy height, indicating that compensatory photosynthetic carbon uptake by undisturbed, later successional subdominant and subcanopy vegetation supported carbon-uptake resistance to disturbance. These findings have implications for ecosystem management and modeling, demonstrating that forests may tolerate considerable leaf-area losses without diminishing rates of carbon uptake. They conclude that the resistance of carbon uptake to moderate disturbance depends not only on replacement of lost leaf area, but also on rapid compensatory photosynthetic carbon uptake during defoliation by emerging later successional species.

Reference: Gough, C. M., B. S. Hardiman, L. E. Nave, G. Bohrer, K. D. Maurer, C. S. Vogel, K.J. Nadelhoffer, and P. S. Curtis. 2013. “Sustained Carbon Uptake and Storage Following Moderate Disturbance in a Great Lakes Forest,” Ecological Applications 23(5), 1202–15. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 21, 2015

Using Ecosystem Experiments to Improve Vegetation Models

Ecosystem responses to rising carbon dioxide (CO2) concentrations are a major source of uncertainty in climate change projections. Data from ecosystem-scale Free-Air CO2 Enrichment (FACE) experiments provide a unique opportunity to reduce this uncertainty. The recent FACE Model–Data Synthesis project aimed to use information gathered in two forest FACE experiments to assess and improve land ecosystem models. A new ‘assumption-centred’ model intercomparison approach was used, in which participating models were evaluated against experimental data based on the ways in which they represent key ecological processes. By identifying and evaluating the main assumptions causing differences among models, the assumption-centred approach produced a clear roadmap for reducing model uncertainty. In a recent paper, researchers explained this approach and summarized the resulting research agenda. They encourage the application of this approach in other model intercomparison projects to fundamentally improve predictive understanding of the Earth system.

Reference: Medlyn, B. E., S. Zaehle, M. G. De Kauwe, A. P. Walker, M. C. Dietze, P. J. Hanson, T. Hickler, A. K. Jain, Y. Luo, W. Parton, I. C. Prentice, P. E. Thornton, S. Wang, Y.-P. Wang, E. Weng, C. M. Iversen, H. R. McCarthy, J. M. Warren, R. Oren, and R. J. Norby. 2015. “Using Ecosystem Experiments to Improve Vegetation Models,” Nature Climate Change 5, 528–34. DOI: 10.1038/nclimate2621. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 19, 2015

Global Model Simulation for 3-D Radiative Transfer Impact on Surface Hydrology

Orographic forcing is an efficient and dominant mechanism for harnessing water vapor into consumable fresh water in the form of precipitation, snowpack, and runoff. Mountain water resources not only support human activities, but are also vital to diverse terrestrial and aquatic ecosystems. To study the long-term effect of solar radiation effect over three-dimensional (3-D) mountains and snow on surface energy and hydrology, the 3-D radiative transfer parameterization developed for the computation of surface solar fluxes has been incorporated into the Community Climate System Model version 4 [(CCSM4); Community Atmosphere Model version 4 (CAM4)/Community Land Model version 4 (CLM4)] global model and applied at a resolution of 0.23°x0.31° over the Rocky Mountains and Sierra Nevada areas in the western United States. In the 3-D radiative transfer parameterization, the surface topography data have been updated from a resolution of 1 km to 90 meters to improve parameterization accuracy. In addition, the upward-flux deviation [3D–plane-parallel (PP)] adjustment has also been modified to ensure that energy balance at the surface is conserved in global climate simulations based on 3-D radiation parameterization. Findings show that deviations of the net surface fluxes are not only affected by 3-D mountains, but also influenced by feedbacks of clouds and snow in conjunction with long-term simulations. Deviations in the sensible heat and surface temperature generally follow the patterns of net surface solar flux. Including 3D-mountain effects significantly increases (decreases) solar radiation at higher (lower) elevations, leading to increased (reduced) snowmelt. Combined with precipitation changes influenced by changes in the surface fluxes, runoff is significantly reduced in mountainous regions after the snow accumulation peaks in April. The 3-D mountain effects could have an important impact on vegetation by changing the energy and water available to plants. With the larger differences in solar radiation, soil moisture, and soil temperature developing in late spring and early summer, changes in photosynthetic rate and plant phenology may affect leaf area index and gross primary production. These findings will be further investigated in the future using longer simulations to quantify the 3-D mountain effects on radiation and the impacts on water and carbon cycles and vegetation globally.

Reference: Lee, W.-L., Y. Gu, K. N. Liou, L. R. Leung, and H.-H. Hsu. 2015. “A Global Model Simulation for 3-D Radiative Transfer Impact on Surface Hydrology over the Sierra Nevada and Rocky Mountains,” Atmospheric Chemistry and Physics 15, 5405-13. DOI: 10.5194/acp-15-5405-2015. (Reference link)

Contact: Dorothy Koch, SC-23.1, (301) 903-0105
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 18, 2015

Darcy’s Law Predicts Widespread Forest Mortality Under Climate Warming

Drought and heat-induced tree mortality is accelerating in many forest biomes as a consequence of a warming climate, resulting in a threat to global forests unlike any in recorded history. Forests store the majority of terrestrial carbon, thus their loss may have significant and sustained impacts on the global carbon cycle. In a recent paper, researchers used a hydraulic corollary to Darcy’s law, a core principle of vascular plant physiology, to predict characteristics of plants that will survive and die during drought under warmer future climates. Plants that are tall with isohydric stomatal regulation, low hydraulic conductance, and high leaf area are most likely to die from future drought stress. Thus, tall trees of old-growth forests are at the greatest risk of loss, which has ominous implications for terrestrial carbon storage. This application of Darcy’s law indicates today’s forests generally should be replaced by shorter and more xeric plants, owing to future warmer droughts and associated wildfires and pest attacks. The Darcy’s corollary also provides a simple, robust framework for informing forest management interventions needed to promote the survival of current forests. Given the robustness of Darcy’s law for predictions of vascular plant function, the researchers conclude with high certainty that today’s forests will be subject to continued increases in mortality rates that result in substantial reorganization of their structure and carbon storage.

Reference: McDowell, N. G., and C. D. Allen. 2015. “Darcy's Law Predicts Widespread Forest Mortality Under Climate Warming,” Nature Climate Change 5, 669–72. DOI: 10.1038/nclimate2641. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 18, 2015

Tall Trees Most Susceptible to Drought Stress

A significant portion of the carbon emitted from fossil fuel combustion is taken up by ocean and terrestrial systems. However, drought and heat-induced tree mortality is accelerating in many forest biomes, resulting in a threat to global forests unlike any in recorded history. Forests store the majority of terrestrial carbon, thus their loss may have significant and sustained impacts on the global carbon cycle. Researchers from Los Alamos National Laboratory have used a hydraulic corollary to Darcy’s law, a core principle of vascular plant physiology, to predict characteristics of plants that will survive and die during drought under warmer future climates. They find that plants that are tall are most likely to die from future drought stress. Thus, tall trees of old-growth forests are at the greatest risk of loss, which has ominous implications for terrestrial carbon storage. This application of Darcy’s law indicates today’s forests generally should be replaced by shorter and more xeric plants, owing to future warmer droughts and associated wildfires and pest attacks. The Darcy’s corollary also provides a simple, robust framework for informing forest management interventions needed to promote the survival of current forests. Given the robustness of Darcy’s law for predictions of vascular plant function, they conclude with high certainty that today’s forests are going to be subject to continued increases in mortality rates that will result in substantial reorganization of their structure and carbon storage.

Reference: McDowell, N. G., and C. D. Allen. 2015. “Darcy's Law Predicts Widespread Forest Mortality Under Climate Warming,” Nature Climate Change 5, 669–72. DOI: 10.1038/nclimate2641. (Reference link)

Contact: Renu Joseph, SC-23.1, (301) 903-9237, Dorothy Koch, SC-23.1, (301) 903-0105, Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 11, 2015

Dual Controls on Carbon Loss During Drought in Peatlands

Peatlands store a third of global soil carbon. Drought and drainage coupled with climate warming present the main threat to these stores. Hence, understanding drought effects and inherent feedbacks related to peat decomposition has been a primary global challenge. However, widely divergent results in recent studies concerning drought effects challenge the accepted paradigm that waterlogging and associated anoxia are the overarching controls locking up carbon stored in peat. By linking field and microcosm experiments, a recent study shows how previously unrecognized mechanisms regulate the buildup of phenolics, which protects stored carbon directly by reducing phenol oxidase activity during short-term drought and, indirectly, through a shift from low-phenolic Sphagnum and herbs to high-phenolic shrubs after long-term moderate drought. The study demonstrates that shrub expansion induced by drought and warming in boreal peatlands might be a long-term, self-adaptive mechanism not only increasing carbon sequestration but also potentially protecting historic soil carbon. The researchers propose that the projected “positive feedback loop” between carbon emissions and drought in peatlands may not occur in the long term.

Reference: Wang, H., C. J. Richardson, and M. Ho. 2015. “Dual Controls on Carbon Loss During Drought in Peatlands,” Nature Climate Change 5(6), 584–87. DOI: 10.1038/nclimate2643. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 02, 2015

Does Day and Night Sampling Reduce Spurious Correlation Between Canopy Photosynthesis and Ecosystem Respiration?

Eddy covariance measurements of carbon dioxide (CO2) exchange have to be partitioned into offsetting gross fluxes, canopy photosynthesis, and ecosystem respiration to understand biophysical controls on the net fluxes. Additionally, independent estimates of canopy photosynthesis (G) and ecosystem respiration (R) are needed to validate and parametrize carbon cycle models that are coupled with climate and ecosystem dynamics models. Carbon flux partitioning methods, however, may suffer from spurious correlation, because derived values of canopy photosynthesis and ecosystem respiration both contain common information on net carbon fluxes at annual time scales.

Researchers hypothesized that spurious correlation between canopy photosynthesis and ecosystem respiration can be minimized using day–night conditional sampling of CO2 exchange, with daytime fluxes dominated by photosynthesis and nighttime fluxes dominated by respiration. To test this hypothesis, the research team derived explicit equations that quantify the degree of spurious correlation between photosynthesis and respiration. Theoretically, day and night samples of net carbon exchange share a different common variable, daytime ecosystem respiration, and the degree of spurious correlation depends upon the variance of this shared variable. This theory was applied to ideal measurements of carbon exchange over a vigorous, irrigated, and frequently harvested alfalfa field in the sunny and windy region of the Sacramento-San Joaquin Delta of California, where soil CO2 efflux is strong. Results showed a correlation coefficient between canopy photosynthesis and ecosystem respiration of -0.79. This relatively high correlation between canopy photosynthesis and respiration was mostly real as the degree of spurious correlation was only -0.32.

This analysis was expanded to the FLUXNET database, which spans a spectrum of climate and plant functional types. On average, the correlation between gross photosynthesis and ecosystem respiration, using day–night sampling, was close to minus one (-0.828 ± 0.130). For perspective, a large fraction of this correlation was real, as the degree of spurious correlation (Eq. (22)) was -0.526. Consequently, the potential for spurious correlation between canopy photosynthesis and ecosystem respiration across the FLUXNET database was moderate. Looking across the database, the researchers found that the least negative spurious correlation coefficients (>-0.3) were associated with seasonal deciduous forests. The most negative spurious correlations coefficients (<-0.7) were associated with evergreen forests found in most boreal climates.

Reference: Baldocchi, D., C. Sturtevant, and FLUXNET contributors. 2015. “Does Day and Night Sampling Reduce Spurious Correlation Between Canopy Photosynthesis and Ecosystem Respiration?” Agricultural and Forest Meteorology 207, 117–26. DOI: 10.1016/j.agrformet.2015.03.010. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 30, 2015

Global Carbon Budget Audit

Over the last 5 decades, monitoring systems have been developed to detect changes in carbon (C) accumulations in the atmosphere and oceans, but the ability to detect changes in the behavior of the global carbon cycle is still hindered by measurement and estimate errors. In a recent study, researchers developed a rigorous and flexible framework for assessing the temporal and spatial components of estimate errors and their impact on uncertainty in net carbon uptake by the biosphere. They present a novel approach for incorporating temporally correlated random error into the error structure of emission estimates. Based on this approach, they conclude that the 2σ uncertainties of the atmospheric growth rate have decreased from 1.2 Pg C yr-1 in the 1960s to 0.3 Pg C yr-1 in the 2000s due to an expansion of the atmospheric observation network. The 2σ uncertainties in fossil fuel emissions have increased from 0.3 Pg C yr-1 in the 1960s to almost 1.0 Pg C yr-1 during the 2000s due to differences in national reporting errors and differences in energy inventories. Lastly, while land use emissions have remained fairly constant, their errors still remain high and thus their global carbon uptake uncertainty is not trivial. Currently, the absolute errors in fossil fuel emissions rival the total emissions from land use, highlighting the extent to which fossil fuels dominate the global carbon budget. Because errors in the atmospheric growth rate have decreased faster than errors in total emissions have increased, a 20% reduction in the overall uncertainty of net carbon global uptake has occurred. Given all the major sources of error in the global carbon budget that could be identified, the results are 93% confident that terrestrial carbon uptake has increased and 97% confident that ocean carbon uptake has increased over the last 5 decades. Thus, arguably one of the most vital ecosystem services that the biosphere currently provides is the continued removal of approximately half of atmospheric carbon dioxide emissions from the atmosphere, although there are certain environmental costs associated with this service, such as the acidification of ocean waters.

Reference: Ballantyne, A. P., R. Andres, R. Houghton, B. D. Stocker, R. Wanninkhof, W. Anderegg, L. A. Cooper, M. DeGrandpre, P. P. Tans, J. B. Miller, C. Alden, and J. W. C. White. 2015. “Audit of the Global Carbon Budget: Estimate Errors and Their Impact on Uptake Uncertainty,” Biogeosciences 12(8), 2565–84. DOI: 10.5194/bg-12-2565-2015. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 27, 2015

Predicting Long-Term Carbon Sequestration in Response to CO2 Enrichment

Large uncertainty exists in model projections of the land carbon sink response to increasing atmospheric carbon dioxide (CO2). Free-Air CO2 Enrichment (FACE) experiments lasting a decade or more have investigated ecosystem responses to a step change in atmospheric CO2 concentration. To interpret FACE results in the context of gradual increases in atmospheric CO2 over decades to centuries, a recent study used a suite of seven models to simulate the Duke Forest and Oak Ridge FACE experiments extended for 300 years of CO2 enrichment. It also determined key modeling assumptions that drive divergent projections of terrestrial carbon uptake and evaluated whether these assumptions can be constrained by experimental evidence. All models simulated increased terrestrial carbon pools resulting from CO2 enrichment, though there was substantial variability in quasi-equilibrium carbon sequestration and rates of change. In two of two models that assume that plant nitrogen uptake is solely a function of soil nitrogen supply, the net primary production response to elevated CO2 became progressively nitrogen limited. In four of five models assuming that nitrogen uptake is a function of both soil nitrogen supply and plant nitrogen demand, elevated CO2 led to reduced ecosystem nitrogen losses and thus progressively relaxed nitrogen limitation. Many allocation assumptions resulted in increased wood allocation relative to leaves and roots, which reduced the vegetation turnover rate and increased carbon sequestration. In addition, self-thinning assumptions had a substantial impact on carbon sequestration in two models. Accurate representation of nitrogen process dynamics (in particular nitrogen uptake), allocation, and forest self-thinning is key to minimizing uncertainty in projections of future carbon sequestration in response to elevated atmospheric CO2.

Reference: Walker, A. P., S. Zaehle, B. E. Medlyn, M. G. De Kauwe, S. Asao, T. Hickler, W. Parton, D. M. Ricciuto, Y.-P. Wang, D. Wårlind, and R. J. Norby. 2015. “Predicting Long–Term Carbon Sequestration in Response to CO2 Enrichment: How and Why Do Current Ecosystem Models Differ?” Global Biogeochemical Cycles 29(4), 476–95. DOI: 10.1002/2014GB004995. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 17, 2015

Differences in Organic Matter from a Range of Soil Types and Ecosystems

Organic matter in soils is a key reservoir for carbon and plays a significant role in nutrient biogeochemical cycling. Because of limited understanding of the molecular composition of soil organic matter (SOM), scientists are challenged to decipher the range of chemical processes in soils and to predict how terrestrial carbon fluxes will respond to changing climatic conditions and land use. To address this need, a team of scientists from the University of Idaho and Department of Energy’s Environmental Molecular Sciences Laboratory (EMSL) extracted SOM from multiple ecosystems using a variety of organic solvents, and then analyzed the SOM using EMSL’s ultra-high resolution mass spectrometry capabilities. The team found different solvents extracted different types of compounds from soils, significantly expanding the ability to sensitively detect and identify the vast suite of diverse organic molecules that compose SOM. These findings enable targeted extraction approaches to elucidate differences in organic matter among soils from different ecosystems. These findings also demonstrate that by using multiple solvents on the same soil material, scientists will be able to obtain a more complete characterization of the organic matter in a specific soil sample. Increased understanding of SOM composition in soils from multiple ecosystems is expected to improve predictions of how terrestrial carbon fluxes will respond to future climate change.

References: Tfaily, M., R. K. Chu, N. Tolic, K. M. Roscioli, C. R. Anderton, L. Paša-Tolic, E. W. Robinson, and N. J. Hess. 2015. “Advanced Solvent Based Methods for Molecular Characterization of Soil Organic Matter by High Resolution Mass Spectrometry,” Analytical Chemistry 87(10), 5206-15. DOI: 10.1021/acs.analchem.5b00116. (Reference link)
(See also)

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 09, 2015

Climate Change and Permafrost Carbon Feedback

Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emissions from these regions and their impact on climate change remain uncertain. In a recent study, researchers find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.

Reference: Schuur, E. A. G., A. D. McGuire, C. Schädel, G. Grosse, J. W. Harden, D. J. Hayes, G. Hugelius. C. D. Koven, P. Kuhry, D. M. Lawrence, S. M. Natali, D. Olefeldt, V. E. Romanovsky, K. Schaefer, M. R. Turetsky, C. C. Treat, and J. E. Vonk. “Climate Change and the Permafrost Carbon Feedback,” Nature 520, 171–79. DOI: 10.1038/nature14338. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 09, 2015

Effect of Temperature on Rate, Affinity, and 15N Fractionation of NO3- During Biological Denitrification in Soils

Soil isotopes are commonly used in environmental, agricultural, and biogeochemical studies to track sources and fate of labeled compounds, and also because they facilitate quantification of the intensity of a process relative to others. In a recent study, researchers worked to (1) elucidate the linear and nonlinear contributions of temperature to the reaction rate of isotopically labeled reactants, (2) highlight whether effects arise in other parameters, and (3) provide a comprehensive sensitivity analysis of kinetic isotopic effects over the concentration-temperature space using mathematical modeling of the effects in (1) and (2). To accomplish this, nine independent experiments of nitrate (NO3-) denitrification were analyzed using the Arrhenius law and the Eyring’s transition-state theory to highlight how temperature affects reaction rate constants, affinities, and kinetic isotopic effects. For temperatures between 20 and 35 °C, the Arrhenius law and the transition-state theory described equally well observed temperature increases in 14NO3- and 15NO3- denitrification rates. These increases were partly caused by an increase in frequency factor and a slight decrease in activation energy (enthalpy and entropy). Parametric analysis also showed that the affinity of 14NO3- and 15NO3- toward a microbial enzyme increased exponentially with temperature and a strong correlation with the rate constants was found. Experimental time and temperature-averaged fractionation factor αP/S showed only a slight increase with increasing temperature (i.e., lower isotopic effects); however, a comprehensive sensitivity analysis in the concentration temperature domain using average thermodynamic quantities estimated here showed a more complex response; αP/S was relatively constant for initial bulk concentrations [NO3-]0 ≤ 0.01 mol kg-1, while substantial nonlinearities developed for [NO3-]0 ≥ 0.01 mol kg-1 and appeared to be strongly correlated with microbial biomass, whose concentration and activity varied primarily as a function of temperature and available substrate. Values of αP/S ranging between 0.9 and 0.98 for the tested temperatures suggested that interpretations of environmental isotopic signatures should include a sensitivity analysis to the temperature as this affects directly the rate constants and affinities in biochemical reactions and may hide process- and source-related isotopic effects.

Reference: Maggi, F., and W. J. Riley. 2015. “The Effect of Temperature on the Rate, Affinity, and 15N Fractionation of NO3- During Biological Denitrification in Soils,” Biogeochemistry 124(1), 235–53. DOI 10.1007/s10533-015-0095-2. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 07, 2015

Phenolic Profile Highlights Disconnect in Root Tissue Quality Predicted by Elemental- and Molecular-Level Carbon Composition

Fine roots constitute a significant source of plant productivity and litter turnover across terrestrial ecosystems, but less is known about the quantitative and qualitative profile of phenolic compounds within the fine-root architecture, which could regulate the potential contribution of plant roots to the soil organic matter pool. To understand the linkage between traditional macro-elemental and morphological traits of roots and their molecular-level carbon chemistry, researchers analyzed seasonal variations in monomeric yields of the free, bound, and lignin phenols in fine roots (distal five orders) and leaves of Ardisia quinquegona. Fine roots contained two-fold higher concentrations of bound phenols and three-fold higher concentrations of lignin phenols than leaves. Within fine roots, the concentrations of free and bound phenols decreased with increasing root order, and seasonal variation in the phenolic profile was more evident in lower-order than in higher-order roots. The morphological and macro-elemental root traits were decoupled from the quantity, composition, and tissue association of phenolic compounds, revealing the potential inability of these traditional parameters to capture the molecular identity of phenolic carbon within the fine-root architecture and between fine roots and leaves. These results highlight the molecular-level heterogeneity in phenolic carbon composition within the fine-root architecture, and imply that traits that capture the molecular identity of the root construct might better predict the decomposition dynamics within fine-root orders.

Reference: Wang, J.-J., N. Tharayil, A. T. Chow, V. Suseela, and H. Zeng. 2015. “Phenolic Profile Within the Fine-Root Branching Orders of an Evergreen Species Highlights a Disconnect in Root Tissue Quality Predicted by Elemental- and Molecular-Level Carbon Composition,” New Phytologist 206(4), 1261–73. DOI: 10.1111/nph.13385. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 24, 2015

Stability of Carbon in Permafrost Soils

Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the post-thaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Using a carbon–nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, researchers show that the permafrost region’s future carbon balance is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg of carbon to 164 Pg carbon losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. Although nitrogen dynamics are highly uncertain, the future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw.

Reference: Koven, C. D., D. M. Lawrence, and W. J. Riley. 2015. “Permafrost Carbon– Climate Feedback is Sensitive to Deep Soil Carbon Decomposability but not Deep Soil Nitrogen Dynamics,” Proceedings of the National Academy of Sciences (USA) 112(12), 3752–57. DOI: 10.1073/pnas.1415123112. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 06, 2015

Decomposition by Ectomycorrhizal Fungi Alters Soil Carbon Storage in Simulation Model

Carbon cycle models often lack explicit belowground organism activity, yet belowground organisms regulate carbon storage and release in soil. Ectomycorrhizal fungi are important players in the carbon cycle because they are a conduit into soil for carbon assimilated by the plant. It is hypothesized that ectomycorrhizal fungi can also be active decomposers when plant carbon allocation to fungi is low. In this study, researchers developed a simulation model of the plant-mycorrhizae interaction where a reduction in plant productivity stimulates ectomycorrhizal fungi to decompose soil organic matter. The model output suggests that ectomycorrhizal activity accounts for a portion of carbon decomposed in soil, but this portion varied with plant productivity and the mycorrhizal carbon uptake strategy simulated. Lower organic matter inputs to soil were largely responsible for reduced soil carbon storage. Using mathematical theory, the researchers demonstrated that biotic interactions affect predictions of ecosystem functions. Specifically, they developed a simple function to model the mycorrhizal switch in function from plant symbiont to decomposer. The study shows that including mycorrhizal fungi with the flexibility of mutualistic and saprotrophic lifestyles alters predictions of ecosystem function.

Reference: Moore, J. A. M., J. Jiang, W. M. Post, and A. T. Classen. 2015. “Decomposition by Ectomycorrhizal Fungi Alters Soil Carbon Storage in a Simulation Model,” Ecosphere 6(3), 29. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 06, 2015

Monoterpenes Play Important Antioxidant Roles, Serve as Sources of Secondary Organic Aerosol Precursors

Despite orders of magnitude difference in atmospheric reactivity and great diversity in biological functioning, little is known about monoterpene speciation in tropical forests. In a recent study, researchers report vertically resolved ambient air mixing ratios for 12 monoterpenes in a central Amazon rainforest, including observations of the highly reactive cis-β-ocimene [160 parts per trillion (ppt)], trans-β-ocimene (79 ppt), and terpinolene (32 ppt), which accounted for an estimated 21% of total monoterpene composition, yet 55% of the upper canopy monoterpene ozonolysis rate. All 12 monoterpenes showed a mixing ratio peak in the upper canopy, with three demonstrating subcanopy peaks in seven of 11 profiles. Leaf-level emissions of highly reactive monoterpenes accounted for up to 1.9% of photosynthesis, confirming light-dependent emissions across several Amazon tree genera. These results suggest that highly reactive monoterpenes play important antioxidant roles during photosynthesis in plants and serve as near-canopy sources of secondary organic aerosol precursors through atmospheric photooxidation via ozonolysis.

Reference: Jardine, A. B., K. J. Jardine, J. D. Fuentes, S. T. Martin, G. Martins, F. Durgante, V. Carneiro, N. Higuchi, A. O. Manzi, and J. Q. Chambers. 2015. “Highly Reactive Light-Dependent Monoterpenes in the Amazon,” Geophysical Research Letters 42(5), 1576–83. DOI: 10.1002/2014GL062573. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 06, 2015

Urgent Need for Warming Experiments in Tropical Forests

Although tropical forests account for only a fraction of the planet’s terrestrial surface, they exchange more carbon dioxide with the atmosphere than any other biome on Earth and thus play a disproportionate role in the global climate. Over the next 20 years, the tropics will experience unprecedented warming, yet exceedingly high uncertainty persists about their potential responses to this imminent climatic change. In a recent study, researchers investigated overall model uncertainty of tropical latitudes and explored the scientific benefits and inevitable trade-offs inherent in large-scale manipulative field experiments. With a Coupled Model Intercomparison Project Phase 5 analysis, they found that model variability in projected net ecosystem production was nearly three times greater in the tropics than for any other latitude. Through a review of the most current literature, they concluded that manipulative warming experiments are vital to accurately predict future tropical forest carbon balance, and they further recommend establishing a network of comparable studies spanning gradients of precipitation, edaphic qualities, plant types, and land use change. In addition, they provide arguments for long-term, single-factor warming experiments that incorporate warming of the most biogeochemically active ecosystem components (i.e., leaves, roots, and soil microbes). Hypothesis testing of underlying mechanisms should be a priority, along with improving model parameterization and constraints. No single tropical forest is representative of all tropical forests; therefore, logistical feasibility should be the most important consideration for locating largescale manipulative experiments.

Reference: Cavaleri, M. A., S. C. Reed, W. K. Smith, and T. E. Wood. 2015. “Urgent Need for Warming Experiments in Tropical Forests,” Global Change Biology 21 (6), 2111–21. DOI: 10.1111/gcb.12860. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 02, 2015

Optimal Stomatal Behavior Around the World

Stomatal conductance (gs) is a key land-surface attribute as it links transpiration, the dominant component of global land evapotranspiration, and photosynthesis, the driving force of the global carbon cycle. Despite the pivotal role of gs in predictions of global water and carbon cycle changes, a global scale database and an associated globally applicable gs model that enable predictions of stomatal behavior are lacking. In a recent study, researchers present a database of globally distributed gs obtained in the field for a wide range of plant functional types (PFTs) and biomes. They found that stomatal behavior differs among PFTs according to their marginal carbon cost of water use, as predicted by the theory underpinning the optimal stomatal model and the leaf and wood economics spectrum. They also demonstrate a global relationship with climate. These findings provide a robust theoretical framework for understanding and predicting gs behavior across biomes and across PFTs that can be applied to regional, continental, and global-scale modeling of ecosystem productivity, energy balance, and ecohydrological processes in a future changing climate.

Reference: Lin, Y.-S., et al. 2015. “Optimal Stomatal Behaviour Around the World,” Nature Climate Change 5, 459–64. DOI: 10.1038/nclimate2550. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 05, 2015

Permafrost Soils and Carbon Cycling

Knowledge of soils in the permafrost region has advanced immensely in recent decades, despite the remoteness and inaccessibility of most of the region and the sampling limitations posed by the severe environment. These efforts have significantly increased estimates of the amount of organic carbon stored in permafrost-region soils and improved understanding of how pedogenic processes unique to permafrost environments built enormous organic carbon stocks during the Quaternary. This knowledge also has called attention to the importance of permafrost-affected soils to the global carbon cycle and the potential vulnerability of the region’s soil organic carbon (SOC) stocks to changing climatic conditions. In a recent review, researchers briefly introduce the permafrost characteristics, ice structures, and cryopedogenic processes that shape the development of permafrost-affected soils and discuss their effects on soil structures and organic matter distributions within the soil profile. They examine the quantity of organic carbon stored in permafrost-region soils, as well as the characteristics, intrinsic decomposability, and potential vulnerability of this organic carbon to permafrost thaw under a warming climate. Overall, frozen conditions and cryopedogenic processes, such as cryoturbation, have slowed decomposition and enhanced sequestration of organic carbon in permafrost-affected soils over millennial timescales. Due to the low temperatures, the organic matter in permafrost soils is often less humified than in more temperate soils, making some portion of this stored organic carbon relatively vulnerable to mineralization upon thawing of permafrost.

Reference: Ping, C. L., J. D. Jastrow, M. T. Jorgenson, G. J. Michaelson, and Y. L. Shur. 2015. “Permafrost Soils and Carbon Cycling,” SOIL 1, 147–71. DOI: 10.5194/soil-1-147-2015. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 27, 2015

Moderate Forest Disturbance as a Stringent Test for Gap and Big-Leaf Models

Disturbance-induced tree mortality is a key factor regulating the carbon balance of a forest, but tree mortality and its subsequent effects are poorly represented processes in terrestrial ecosystem models. Thus unclear is whether models can robustly simulate moderate (noncatastrophic) disturbances, which tend to increase biological and structural complexity and are increasingly common in aging U.S. forests. Researchers recently tested whether three forest ecosystem models—Biome-BGC (BioGeochemical Cycles), a classic big-leaf model, and the ZELIG and ED (Ecosystem Demography) gap-oriented models—could reproduce the resilience to moderate disturbance observed in an experimentally manipulated forest (Forest Accelerated Succession Experiment in northern Michigan, where 38% of canopy dominants were stem girdled and compared to control plots). Each model was parameterized, spun up, and disturbed following similar protocols and run for 5 years post-disturbance. The models replicated observed declines in aboveground biomass well. Biome-BGC captured the timing and rebound of observed leaf area index (LAI), while ZELIG and ED correctly estimated the magnitude of LAI decline. None of the models fully captured the observed post-disturbance carbon fluxes, in particular gross primary production or net primary production (NPP). Biome-BGC NPP was correctly resilient but for the wrong reasons, and could not match the absolute observational values. ZELIG and ED, in contrast, exhibited large, unobserved drops in NPP and net ecosystem production. The biological mechanisms proposed to explain the observed rapid resilience of the carbon cycle typically are not incorporated by these or other models. Thus, an open question is whether most ecosystem models will simulate correctly the gradual and less extensive tree mortality characteristic of moderate disturbances.

Reference: Bond-Lamberty, B., J. P. Fisk, J. A. Holm, V. Bailey, G. Bohrer, and C. M. Gough. 2015. “Moderate Forest Disturbance as a Stringent Test for Gap and Big-Leaf Models,” Biogeosciences 12(2), 513–26. DOI: 10.5194/bg-12-513-2015. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 08, 2015

Dimethyl Sulfide Emissions in the Amazon Rainforest

Surface-to-atmosphere emissions of dimethyl sulfide (DMS) may impact global climate through the formation of gaseous sulfuric acid, which can yield secondary sulfate aerosols and contribute to new particle formation. While oceans are generally considered the dominant sources of DMS, a shortage of ecosystem observations prevents an accurate analysis of terrestrial DMS sources. Using mass spectrometry, researchers recently quantified ambient DMS mixing ratios within and above a primary rainforest ecosystem in the central Amazon Basin in real time (2010–2011) and at high vertical resolution (2013–2014). Elevated, but highly variable DMS mixing ratios were observed within the canopy, showing clear evidence of a net ecosystem source to the atmosphere during both day and night in both the dry and wet seasons. Periods of high DMS mixing ratios lasting up to 8 hours [up to 160 parts per trillion (ppt)] often occurred within the canopy and near the surface during many evenings and nights. Daytime gradients showed mixing ratios (up to 80 ppt) peaking near the top of the canopy as well as near the ground following a rain event. The spatial and temporal DMS distribution suggests that ambient levels and their potential climatic impacts are dominated by local soil and plant emissions. A soil source was confirmed by measurements of DMS emission fluxes from Amazon soils as a function of temperature and soil moisture. Furthermore, light- and temperature-dependent DMS emissions were measured from seven tropical tree species. This study has important implications for understanding terrestrial DMS sources and their role in coupled land-atmosphere climate feedbacks.

Reference: Jardine, K., A. M. Yañez-Serrano, J. Williams, N. Kunert, A. Jardine, T. Taylor, L. Abrell, P. Artaxo, A. Guenther, C. N. Hewitt, E. House, A. P. Florentino, A. Manzi, N. Higuchi, J. Kesselmeier, T. Behrendt, P. R. Veres, B. Derstroff, J. D. Fuentes, S. T. Martin, and M. O. Andreae. 2015. “Dimethyl Sulfide in the Amazon Rainforest,” Global Biogeochemical Cycles 29(1), 19–32. DOI: 10.1002/2014GB004969. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 08, 2015

Global Leaf Trait Database Supports Earth System Models

In science, researchers collaborate so that they can complement existing disciplinary expertise, gain access to specialized equipment, or expand the depth and breadth of datasets that can be used to derive new knowledge. Motivated by this latter objective, a research team has compiled a global database (GlobResp) that details rates of leaf dark respiration and associated traits from sites that span Arctic tundra to tropical forests. This database builds on earlier research and was supplemented by recent field campaigns and unpublished data. In keeping with other trait databases, GlobResp provides insights on how physiological traits, especially rates of dark respiration, vary as a function of environment and how that variation can be used to inform terrestrial biosphere models and land surface components of Earth system models. Although an important component of plant and ecosystem carbon budgets, respiration has only limited representation in models. This database gives users a unique perspective of the climatic controls on respiration, thermal acclimation and evolutionary adaptation of dark respiration, and insights into the covariation of respiration with other leaf traits.

References:

  1. Atkin, O. K., et al. 2015. “Global Variability in Leaf Respiration in Relation to Climate, Plant Functional Types, and Leaf Traits,” New Phytologist 206(2), 614–36. DOI: 10.1111/nph.13253. (Reference link)
  2. Wullschleger, S. D., J. M. Warren, and P. E. Thornton. 2015. “Leaf Respiration (GlobResp)–Global Trait Database Supports Earth System Models,” New Phytologist 206(2), 483–85. DOI: 10.1111/nph.13364. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 01, 2015

Net Primary Production of Temperate Deciduous Forest Exhibits Threshold Response to Increasing Disturbance Severity

The global carbon balance is vulnerable to disturbances that alter terrestrial carbon storage. Disturbances to forests occur along a continuum of severity, from low-intensity disturbance causing the mortality or defoliation of only a subset of trees to severe stand-replacing disturbance that kills all trees; yet, considerable uncertainty remains in how forest production changes across gradients of disturbance intensity. In a recent study, researchers used a gradient of tree mortality in an upper Great Lakes forest ecosystem to: (1) quantify how aboveground wood net primary production (ANPPw) responds to a range of disturbance severities and 2) identify mechanisms supporting ANPPw resistance or resilience following moderate disturbance. They found that ANPPw declined nonlinearly with rising disturbance severity, remaining stable until > 60 % of the total tree basal area senesced. As upper canopy openness increased from disturbance, greater light availability to the subcanopy enhanced the leaf-level photosynthesis and growth of this formerly light-limited canopy stratum, compensating for upper canopy production losses and a reduction in total leaf area index (LAI). As a result, whole-ecosystem production efficiency (ANPPw/LAI) increased with rising disturbance severity, except in plots beyond the disturbance threshold. These findings provide a mechanistic explanation for a nonlinear relationship between ANPPw and disturbance severity, in which the physiological and growth enhancement of undisturbed vegetation is proportional to the level of disturbance until a threshold is exceeded. These results have important ecological and management implications, demonstrating that in some ecosystems moderate disturbance levels minimally alter forest production.

Reference: Stuart-Haëntjens, E., P. S. Curtis, R. T. Fahey, C. S. Vogel, and C. M. Gough. 2015. “Net Primary Production of a Temperate Deciduous Forest Exhibits a Threshold Response to Increasing Disturbance Severity,” Ecology 96, 2478–87. (Reference link)

Contact: Jared DeForest, SC-23, (301) 903-3251, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 05, 2014

Multiscale Model Unifies Simulation of Surface and Groundwater Flow

Modeling hydrological processes in ecosystems containing both surface water and groundwater is crucial for understanding fluid flow in general, and, more specifically, for understanding the cycling of organic and inorganic elements and the availability of nutrients to microbes and plants. Such understanding could lead to approaches to better control carbon and water cycles, mitigate contamination, and enhance nutrient availability for bioenergy crops. However, a long-standing challenge has been that models use separate sets of equations to describe fluid flow in surface water and groundwater, thus requiring complex approaches to couple equations. Now, scientists from the University of Central Florida and Pacific Northwest National Laboratory have developed a unified multiscale model that uses a single set of equations to simultaneously simulate fluid flow in an ecosystem containing both surface water and groundwater. Simulations were performed using the Cascade supercomputer at the Environmental Molecular Sciences Laboratory, one of the Department of Energy’s scientific user facilities. The team applied the modeling approach to the Disney Wilderness Preserve in Kissimmee, Florida, where active field monitoring and measurements are ongoing to understand hydrological and biogeochemical processes. The simulation results demonstrated that the Disney Wilderness Preserve is subject to frequent changes in soil saturation, geometry and volume of surface waterbodies, and groundwater and surface water exchange. The unified multiscale model is expected to lead to a better understanding of fluid flow in active groundwater and surface water interaction zones, such as wetlands, which play important roles in global cycling of carbon and nitrogen, degradation of metals and organic contaminants, and production and mitigation of greenhouse gases.

References: Yang, X., C. Liu, Y. Fang, R. Hinkle, H.-Y. Li, V. Bailey, and B. Bond-Lamberty. 2015. “Simulations of Ecosystem Hydrological Processes Using a Unified Multi-Scale Model,” Ecological Modelling 296,93–101. DOI: 10.1016/j.ecolmodel.2014.10.032. (Reference link)
Further information

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 13, 2014

Contemporary Terrestrial Biosphere May Be More CO2 Limited than Previously Thought

In plants with C3 photosynthetic pathways, CO2 concentrations drop considerably along leaf mesophyll diffusion pathways from sub-stomatal cavities to chloroplasts where CO2 assimilation occurs. Global carbon cycle models have not explicitly represented this internal drawdown, overestimating CO2 available for carboxylation and underestimating photosynthetic responsiveness to atmospheric CO2. Researchers at Oak Ridge National Laboratory sought to determine how mesophyll diffusion affects the global land CO2 fertilization effect estimated by global carbon models. The team found that current carbon cycle models underestimate by 16% the long-term responsiveness of global terrestrial productivity to CO2 fertilization. This underestimation of CO2 fertilization is caused by an inherent model structural deficiency related to a lack of explicit representation of CO2 diffusion inside leaves, which results in an overestimation of CO2 available at the carboxylation site. The magnitude of CO2 fertilization underestimation matches the long-term positive growth bias in the historical atmospheric CO2 predicted by Earth system models. This finding implies that the contemporary terrestrial biosphere is more CO2 limited than previously thought and will lead to improved understanding and modeling of carbon-climate feedbacks.

Reference: Sun, Y., L. Gu, R. E. Dickinson, R. J. Norby, S. G. Pallardy, and F. M. Hoffman. 2014. “Impact of Mesophyll Diffusion on Estimated Global Land CO2 Fertilization,” Proceedings of the National Academy of Sciences (USA) 111(44), 15,774-779. DOI: 10.1073/pnas.1418075111. (Reference link)

Contact: Daniel Stover, SC-23.1, (301) 903-0289, Mike Kuperberg, SC-23.1, (301) 903-3281
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 13, 2014

Elevated CO2 Suppresses Dominant Plant Species in a Mixed-Grass Prairie

Climate controls vegetation distribution across the globe, with some vegetation types being more vulnerable to climate change and others more resistant. Because resistance and resilience can influence ecosystem stability and determine how communities and ecosystems respond to climate change, it is important to evaluate the potential for resistance in future ecosystem function. In a mixed-grass prairie in the northern Great Plains, researchers utilized a large field experiment to test the effects of elevated CO2, warming, and summer irrigation on plant community structure and productivity. This study sought to understand changes to both stability in plant community composition and biomass production. The researchers found that the independent effects of CO2 and warming on community composition and productivity depend on interannual variation in precipitation and that the effects of elevated CO2 are not limited to water saving because they differ from those of irrigation. They also show that production in this mixed-grass prairie ecosystem is not only relatively resistant to interannual variation in precipitation, but also rendered more stable under elevated CO2 conditions. This increase in production stability is the result of altered community dominance patterns: Community evenness increases as dominant species decrease in biomass under elevated CO2. In many grasslands that serve as rangelands, the economic value of the ecosystem is largely dependent on plant community composition and the relative abundance of key forage species. These results have implications for how native grasslands are managed in the face of changing climate.

Reference: Zelikova, T. J., D. M. Blumenthal, D. G. Williams, L. Souza, D. R. LeCain, J. Morgan, and E. Pendall. 2014. “Long-Term Exposure to Elevated CO2 Enhances Plant Community Stability by Suppressing Dominant Plant Species in a Mixed-Grass Prairie,” Proceedings of the National Academy of Sciences (USA) 111(43), 15,456-461. DOI: 10.1073/pnas.1414659111. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


May 02, 2014

Faster Decomposition Under Increased Atmospheric CO2 Limits Soil Carbon Storage

Carbon dioxide (CO2) is released to the atmosphere when humans burn oil, coal, and gasoline, and it is the major cause of global warming. Soils can store carbon, helping to counteract rising CO2. Carbon accumulates in soil through many years of plant photosynthesis, but also is lost from soil as microscopic organisms, mostly bacteria and fungi, decompose soil carbon, converting it back to CO2 and releasing it to the atmosphere. The balance of these two processes and the future of the soil carbon sink are uncertain. How much will soil organic carbon persist, and how much will soil microorganisms convert back to CO2, returning it to the atmosphere? This study compared data gathered from experiments around the world with models of the soil carbon cycle to test how carbon release from soil by microorganisms responds to rising CO2. The main finding was surprising: increased plant growth caused by rising atmospheric CO2 was associated with higher rates of CO2 release from soil. On balance, the findings suggest that if rising CO2 enhances carbon storage in soil at all, the effect will be small. These results indicate that soil carbon may not be as stable as previously thought, and that soil microorganisms exert more direct control on long-term carbon accumulation than currently represented in global models.

Reference: Van Groenign, K. J., X. Qi, C. W. Osenberg, Y. Luo, and B. A. 2014. “Faster Decomposition Under Increased Atmospheric CO2 Limits Soil Carbon Storage,” Science 344(6183), 508-509. DOI:10.1126/science.1249534. (Reference link)

Contact: Renu Joseph, SC-23.1, (301) 903-9237, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 01, 2014

Isoprene Fluxes from an Oak-Dominated Temperate Forest

Isoprene is a biogenic volatile organic compound. Its oxidation in the atmosphere affects both the production of tropospheric ozone and secondary aerosol formation. Isoprene production by plants, therefore, has implications for the control of regional air quality and global climate change. Scientists at Oak Ridge National Laboratory recently conducted a study to understand these isoprene emissions and to test predictive models at multiple scales. The study took place at the Missouri Ozark AmeriFlux (MOFLUX) site in central Missouri, an oak-hickory dominated forest. Ecosystem fluxes of isoprene emissions were measured during the 2011 growing season. The isoprene flux measurements were used to test understanding of the controls on isoprene emission from hourly to seasonal timescales with a state-of-the-art emission model, MEGAN (Model of Emissions of Gases and Aerosols from Nature). Isoprene emission rates observed during the drought of 2011 reached 53.3 mg m-2 h-1 (217 nmol m-2 s-1), the highest ever recorded for any ecosystem in the world. The MEGAN model correctly predicted isoprene emission rates before drought, but its performance deteriorated as the drought progressed (in response to water stress). Overall, MEGAN’s performance was robust and could explain 90% of the observed variance in the measured fluxes, but the response of isoprene emission to drought stress is a major source of uncertainty. Since isoprene is chemically reactive in the atmosphere, it is critically important to understand these emissions as well as to incorporate this process into atmosphere-biosphere models.

Reference: Potosnak, M. J., L. LeStourgeon, S. G. Pallardy, K. P. Hosman, L. H. Gu, T. Karl, C. Gerone, and A. B. Guenther. 2014. “Observed and Modeled Ecosystem Isoprene Fluxes from an Oak-Dominated Temperate Forest and the Influence of Drought Stress,” Atmospheric Environment 84, 314–22. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 08, 2014

Symbiotic Fungi Inhabiting Plant Roots Have Major Impact on Atmospheric Carbon

Of central concern to climate change science is the potential for natural feedbacks to the warming currently under way as a result of anthropogenic CO2 emissions. Soil is the largest reservoir of carbon in the terrestrial biosphere, containing more than that already found in the atmosphere and biomass combined. If soils were to lose even a small fraction of their carbon, climate could change rapidly with important repercussions for U.S. policy on topics as disparate as food security and coastal inundation. To date, it is has been difficult to identify the factors controlling gains of soil carbon on local to global scales. In recent study, researchers show that mycorrhizal fungi—symbiotic fungi on plant roots—control the quantity of carbon in today’s soils. Using global datasets, they found that the soil in ecosystems dominated by ecto- and ericoid mycorrhizal fungi contains ~70% more carbon than those dominated by arbuscular mycorrhizal fungi. In their analysis, the effect of mycorrhizal type on soil carbon pools was of far larger consequence than the effects of an ecosystem’s productivity, its climate (i.e., temperature and precipitation) or the physical properties of its soil (e.g., clay content). While the mechanism accounting for the difference in soil carbon storage is still debated, it appears that competition for nitrogen in the soil provides the best answer. Ecto- and ericoid mycorrhizal fungi produce many different types of enzymes that they release into the soil in an effort to unlock the nitrogen bound to carbon pools in soil. These fungi also are very effective competitors for nitrogen, making it very scarce to other decomposers in the soil, reducing their biomass and hence the rate of decomposition. By contrast, arbuscular mycorrhizal fungi lack many of these enzyme systems and decomposition rates are rapid. Importantly, this research links the traits of mycorrhizal fungi to carbon storage at the global scale—from tropical forests to the far northern reaches of the boreal forest—suggesting that decomposer competition for nutrients exerts fundamental control over the terrestrial carbon cycle. Whether climate change alters the distribution of these different fungal species remains to be seen, but increases in the abundance or geographical spread of arbuscular mycorrhizal may portend a significant, biologically controlled positive feedback to the climate system.

Reference: Averill, C., B. L. Turner, and A. C. Finzi. 2014. “Mycorrhiza-Mediated Competition Between Plants and Decomposers Drives Soil Carbon Storage,” Nature 505, 543-45. DOI:10.1038/nature12901. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


December 17, 2013

Improving Methods for Measuring Mesophyll Conductance in Response to CO2

Current studies with the chlorophyll fluorescence-based (i.e., variable J) method have reported that mesophyll conductance rapidly decreases with increasing intercellular CO2 partial pressures or decreasing solar irradiance. However, the current method can produce an artifactual dependence of gas conductance in the leaf. A new study at Oak Ridge National Laboratory has identified deficiencies in the chlorophyll fluorescence-based (i.e., variable J) and carbon isotope-based (i.e., online carbon isotope discrimination) methods for measuring mesophyll conductance and has proposed effective solutions. They also derived a new photosynthesis carbon isotope discrimination equation that considers multiple CO2 sources for carboxylation. The significance of this work lies in our understanding of mesophyll conductance, since it is crucial for understanding and predicting responses of photosynthesis to increases in atmospheric CO2. As a result of this study, scientists will be able to improve key methods for measuring mesophyll conductance that will improve the representation of photosynthesis and carbon isotope discrimination in carbon cycle models. Additionally, since photosynthesis is the foundation for the terrestrial carbon isotope ecology, this study will facilitate the application of carbon isotopes in studying ecological processes.

Reference: Gu, L., and Y. Sun. 2013. “Artefactual Responses of Mesophyll Conductance to CO2 and Irradiance Estimated with the Variable J and Online Isotope Discrimination Methods,” Plant, Cell and Environment, DOI:10.1111/pce.12232. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 25, 2013

Spatial Distribution of U.S. Anthropogenic Methane Sources

This study, jointly funded by the Department of Energy’s Atmospheric Radiation Measurement (ARM) and Terrestrial Ecosystem Science (TES) programs along with support from the National Science Foundation and National Aeronautics and Space Administration, sought to quantitatively estimate the spatial distribution of anthropogenic methane sources in the United States by combining comprehensive atmospheric methane observations, extensive spatial datasets, and a high-resolution atmospheric transport model. Using eddy covariance tower and aircraft-based atmospheric observations of methane, along with a high-resolution atmospheric transport model (STILT), results were compared to inventories from the U.S. Environmental Protection Agency and Emissions Database for Global Atmospheric Research (EDGAR) database. Current inventories from the database underestimate methane emissions nationally by a factor of ~1.5 to ~1.7. This study indicates that emissions due to ruminant animals (livestock) and manure are up to twice the magnitude of existing inventories. The discrepancy in methane source estimates is particularly pronounced in the south-central United States, where total emissions are ~2.7 times greater than in most inventories and account for ~24% of national emissions. The spatial patterns of emission fluxes and observed methane-propane correlations indicate that fossil fuel extraction and refining are major contributors (~45%) in the south-central United States. This result suggests that regional methane emissions due to fossil fuel extraction and processing could be nearly five times larger than in EDGAR, the most comprehensive global methane inventory. These results cast doubt on a recent decision to downscale estimates of national natural gas emissions by 25-30%. Overall, the investigators conclude that methane emissions associated with both the animal husbandry and fossil fuel industries have larger greenhouse gas impacts than indicated by existing inventories.

Reference: Miller, S. M., S. C. Wofsy, A. M. Michalak, E. A. Kort, A. E. Andrews, S. C. Biraud, E. J. Dlugokencky, J. Eluszkiewiczf, M. L. Fischer, G. Janssens-Maenhout, B. R. Miller, J. B. Miller, S. A. Montzkad, T. Nehrkornf, and C. Sweeney. 2013. “Anthropogenic Emissions of Methane in the United States,” Proceedings of the National Academy of Sciences (USA) 110(50), 20018-22. DOI:10.1073/pnas.1314392110. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Rickey Petty, SC-23.1, (301) 903-5548, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 15, 2013

Stability of Soil Organic Carbon: Impacts of Particle Size

Studies comparing the mineralization rate of organic carbon (C) associated with different particle size fractions are extremely limited. Organic C associated with the mineral fraction, in particular, is thought to have long residence times. Studies of C decomposition as a function of particle size should improve the representation of long-term C stabilization processes in terrestrial carbon cycle models. A recent study at Oak Ridge National Laboratory sought to quantify decomposition of native soil organic C and a newly added C substrate from both particulate and mineral soil pools. Five different soils were fractionated into particulate (> 53 µm) and mineral (< 53 µm) fractions, radiolabeled with glucose, and incubated for 150 days. Results indicated that the mineralization of native soil organic C was higher from the particulate fraction than the mineral fraction, while mineralization of glucose was similar from both fractions. Furthermore, native organic C in the soil mineral fraction was observed to be resistant to decomposition, in contrast to added glucose which was readily decomposed. Glucose additions therefore appear to be an inadequate surrogate for quantifying long residence times of organic C associated with soil minerals. Although we currently lack adequate experimental data on mineral-associated fractions, this study represents a significant step toward improving our understanding of long-term C stability of soil organic matter and representing these mechanisms in ecosystem-scale models.

Reference: Jagadamma, S., J. M. Steinweg, M. A. Mayes, G. Wang, and W. M. Post. 2013. “Decomposition of Added and Native Organic Carbon from Physically Separated Fractions of Diverse Soils,” Biology and Fertility of Soils, DOI:10.1007/s00374-013-0879-2. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 08, 2013

Worldwide Dataset Demonstrates Importance of CO2 Diffusion in Leaves on Photosynthesis

Oak Ridge National Laboratory scientists used worldwide datasets gathered through an online virtual laboratory for photosynthesis research (leafweb.ornl.gov) to determine the effects of CO2 diffusion inside leaves (i.e., mesophyll conductance) on photosynthesis across all major plant functional types and climates.   Molded mesophyll conductance (gm) generally has been assumed to be infinitely large.   Synthesis of LeafWeb data from over 130 C3 photosynthetic species in different countries showed that mesophyll conductance of most species is as important as stomatal conductance in affecting photosynthesis.   The study found that standard assumptions of an infinite mesophyll conductance resulted in a major underestimation of CO2 assimilation capacities of the photosynthetic machinery and a distortion of relationships between key biochemical processes.   Based on the study’s findings, a new functional model is proposed to facilitate the representation of mesophyll conductance in global carbon cycle models.   This study will lead to better understanding of photosynthetic processes under natural conditions and development of better global carbon cycle models.   A virtual laboratory like LeafWeb is a cost effective, efficient tool for promoting international collaboration, collecting spatially distributed datasets of global importance, and conducting synthesis research that would otherwise be difficult to carry out.

Reference: Sun, Y., L. Gu, R. E. Dickinson, S. G. Pallardy, J. Baker, Y. Cao, F. M. DaMatta, X. Dong, D. Ellsworth, D. Van Goethem, A. M. Jensen, B. E. Law, R. Loos, S. C. Vitor Martins, R. J. Norby, J. Warren, D. Weston, and K. Winter. 2013. “Asymmetrical Effects of Mesophyll Conductance on Fundamental Photosynthetic Parameters and Their Relationships Estimated from Leaf Gas Exchange Measurements,” Plant, Cell and Environment, DOI:10.1111/pce.12213. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 04, 2013

Sagebrush Carrying Out Hydraulic Lift Enhances Surface Soil Nitrogen Cycling and Nitrogen Uptake into Inflorescences

Plant roots are conduits for water flow from soil to leaves and from wetter to drier soil. This hydraulic redistribution through root systems occurs in soils worldwide and can enhance stomatal opening, transpiration, and plant carbon gain. For decades, upward hydraulic lift (HL) of deep water through roots into dry, litter-rich, surface soil also has been hypothesized to enhance nutrient availability to plants by stimulating microbe controlled nutrient cycling, but this link has not been demonstrated in the field. Working in sagebrush-steppe, where water and nitrogen limit plant growth and reproduction and where HL occurs naturally during summer drought, Department of Energy scientists from the Marine Biological Laboratory slightly augmented deep soil water availability (HL+) to plants throughout the summer growing season. The treated sagebrush lifted greater amounts of water than control plants and had slightly less negative predawn and midday leaf water potentials. Soil respiration also was augmented under HL+ plants. At summer’s end, they observed increased rates of nitrogen cycling in surface soil layers around HL+ plants and increased nitrogen uptake into HL+ plants’ inflorescences as sagebrush set seed. These treatment effects persisted even though unexpected monsoon rainstorms arrived during assays and increased surface soil moisture around all plants. Simulation models from ecosystem to global scales have just begun to include effects of hydraulic redistribution on water and surface energy fluxes. Results from this field study indicate that plants carrying out HL also can substantially enhance decomposition and nitrogen cycling in surface soils.

Reference: Cardon, Z. G., J. M. Stark, P. M. Herron, and J. A. Rasmussen. 2013. “Sagebrush Carrying Out Hydraulic Lift Enhances Surface Soil Nitrogen Cycling and Nitrogen Uptake into Inflorescences,” Proceedings of the National Academy of Sciences (USA) 110, 18988-991. DOI:10.1073/pnas.1311314110. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 30, 2013

Faster Organic Matter Decomposition Predicted for Well-Drained Boreal Soils Following Permafrost Degradation

Roots and litterfall can release readily decomposable carbon sources into soil. This newly added carbon may increase or suppress the decomposition of older soil organic matter phenomena known as positive or negative “priming effects.” In temperate regions, recent research suggests priming effects can be a critical mechanism controlling soil carbon dynamics, yet virtually nothing is known about priming effects in boreal ecosystems. To investigate the importance of priming effects in boreal forest soils, researchers at Argonne National Laboratory developed a mechanistic model that can simulate simultaneously occurring soil physical, chemical, biological, and hydrological processes and their interactions. The model was then used to perform sensitivity analyses for two black spruce forest sites, with and without underlying permafrost. Overall, priming effects were strongly controlled by the intensity and frequency of dissolved organic carbon (DOC) inputs to soil. Greater priming effects were predicted for the site with favorable soil water flow than for the site where soil water flow was limited because water flow can carry DOC to deep soil layers, which are rich in organic carbon in boreal soils. Modeling results suggest that priming effects might be accelerated for sites where permafrost degradation leads to drier soil conditions and favorable water transport into deeper layers. In addition to DOC dynamics, priming effects were most sensitive to changes in the composition of solid soil organic carbon, followed by biomass changes in the soil microbial community. The findings from this model sensitivity analysis highlight the urgent need to better study these key parameters in future laboratory and field experiments in permafrost regions.

Reference: Fan, Z., J. D. Jastrow, C. Liang, R. Matamala, and R. M. Miller. 2013. “Priming Effects in Boreal Black Spruce Forest Soils: Quantitative Evaluation and Sensitivity Analysis,” PLoS ONE 8, e77880. DOI:10.1371/journal.pone.0077880. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 08, 2013

Earthworms Affect Forest Soil Carbon Stabilization

The role of soils in mitigating increases in atmospheric carbon dioxide (CO2) is uncertain, in part due to the complex biotic and abiotic interactions determining soil carbon change. Earthworms, in particular, interact with the physical and chemical protection mechanisms of organic matter, major determinants of carbon storage capacity of soils. Protection of enhanced plant litter inputs from rapid decomposition by soil aggregates was a key mechanism facilitating the carbon gain observed in surface soils of the sweetgum forest Free-Air CO2 Enrichment (FACE) experiment in Oak Ridge, TN. To evaluate whether two earthworm species with different feeding behaviors played a role in soil aggregate formation and the stabilization of leaf and/or root litter in these aggregates, Department of Energy researchers conducted a laboratory incubation experiment with earthworms plus isotopically labeled soil and plant materials from the sweetgum FACE site. Compared to the experimental treatments without worms, the presence of either earthworm species increased the formation of soil macroaggregates (greater than 250 µm in diameter). The invasive European earthworm species, which feeds on both plant residues and soil organic matter, incorporated significant amounts of leaf- and root-derived carbon, in addition to soil-derived carbon, into newly formed aggregates. In contrast, the native earthworm species, which feeds mostly on soil organic matter, produced almost twice as many aggregates, but hardly any of the carbon in these aggregates was derived from the added plant materials. Overall, these findings suggest that the presence or absence of earthworms—and specifically the type of earthworm—could be an important factor contributing to the fate of increased plant litter produced as a result of rising atmospheric CO2 concentrations.

Reference: Sánchez-de León, Y., J. Lugo-Pérez, D. H. Wise, J. D. Jastrow, and M. A. González-Meler. 2014. “Aggregate Formation and Carbon Sequestration by Earthworms in Soil from a Temperate Forest Exposed to Elevated Atmospheric CO2: A Microcosm Experiment,” Soil Biology and Biochemistry 68, 223–30. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 03, 2013

Combining Ground Station and Satellite Data for Better Estimates of CO2 Emissions

Scientists from Lawrence Berkeley National Laboratory present one of the first estimates of the global distribution of CO2 surface fluxes using total column CO2 measurements retrieved by the SRON-KIT RemoTeC algorithm from the Greenhouse gases Observing SATellite (GOSAT). The international research team used a series of calculations to combine data from the satellite over an 18-month period with nearly 17,000 surface-level observations from 132 locations during the same period. The team used this data to estimate the CO2 sources and sinks around the world. Their global scale results compared favorably to independent estimates made by government agencies, while at regional scales some differences raised questions for future exploration. The study shows that assimilating the bias corrected satellite data on top of surface CO2 data reduces the estimated global CO2 land sink and shifts the net terrestrial carbon uptake from the tropics to the extratropics. It is concluded that while GOSAT total column CO2 provides useful constraints for source-sink inversions, small spatiotemporal biases €"beyond what can be detected using current validation techniques €"have serious consequences for optimized fluxes, even aggregated over continental scales.

Reference: Basu, S., S. Guerlet, A. Butz, S. Houweling, O. Hasekamp, I. Aben, P. Krummel, P. Steele, R. Langenfeld, M. Torn, S. Biraud, B. Stephens, A. Andrews, and D. Worthy. 2013. “Global CO2 Fluxes Estimated from GOSAT Retrievals of Total Column CO2,” Atmospheric Chemistry and Physics 13, 8695-717. DOI:10.5194/acp-13-8695-2013. (Reference link)

Contact: Wanda Ferrell, SC-23.1, (301) 903-0043, Mike Kuperberg, SC-23.1, (301) 903-3281, Rickey Petty, SC-23.1, (301) 903-5548, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


August 19, 2013

Accounting for Root-Driven Priming of Soil Organic Matter Decomposition Can Improve Model Performance

The interactions between plants and soil play a central role in the functioning of terrestrial ecosystems and the global carbon cycle. Most of these interactions take place in the rhizosphere, the zone of soil that surrounds and is directly influenced by plant roots. The rhizosphere priming effect is a key interaction between living roots and associated rhizosphere organisms that has the potential to alter soil organic matter dynamics by stimulating or suppressing decomposition rates. In a review for New Phytologist, a series of modeling exercises explored how the rhizosphere priming effect might result from an evolutionarily stable mutualistic association between plants and rhizosphere microbes, and how the physiological responses of rhizosphere microbes to different types of plant-derived substrates might help to explain the existence of both positive and negative priming effects. Further, the ability of a commonly used ecosystem model to correctly simulate data from the U.S. Department of Energy-sponsored Duke Free-Air CO2 Enrichment (FACE) experiment was significantly improved by including a priming-induced acceleration of soil organic matter decomposition in response to atmospheric CO2 enrichment. A 40% increase over ambient decay rates for one of the model’s soil organic matter pools enabled better predictions of the increases in plant growth and nitrogen uptake as well as the lack of change in soil carbon observed in the elevated CO2 treatment. This model-data-comparison case study demonstrates the potential importance of the rhizosphere priming effect in terrestrial ecosystems and highlights the value of research efforts to enable its mechanistic incorporation into future ecosystem and Earth system models.

Reference: Cheng, W., W. J. Parton, M. A. Gonzalez-Meler, R. Phillips, S. Asao, G. G. McNickle, E. Brzostek, and J. D. Jastrow. 2013. “Synthesis and Modeling Perspectives of Rhizosphere Priming,” New Phytologist 201, 31-44. DOI: 10.1111/nph.12440. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.2 Biological Systems Science Division, BER


July 23, 2013

Isoprene Discovered to be an Antioxidant

A fraction of net carbon assimilation can be re-released as isoprene by many tropical plants; however, much uncertainty remains about its biological significance. A comprehensive analysis of the suite of isoprene oxidation products in plants has not been performed and production relationships with environmental stress have not been described. Traditionally, isoprene is assumed to only be oxidized in the atmosphere to methyl vinyl ketone, methacrolein, and 3-methly furan. Abiotic stress (e.g., high temperature, light, and freeze-thaw) is known to induce oxidative stress in plants. A study conducted at Lawrence Berkeley National Laboratory, in conjunction with the Department of Energy’s GOAmazon campaign in Brazil, aimed to identify and quantify emissions of potential isoprene oxidation products from mango tree leaves as a function of temperature. Isoprene oxidation products including methyl vinyl ketone, methacrolein, and 3-methyl furan were measured as direct emissions from mango trees grown in environmental chambers. Isoprene oxidation also was measured in a tropical mesocosm (Bisophere 2). These measurements were taken at the leaf, branch, mesocosm, and whole ecosystem scale using chamber and tower sampling systems. The study’s results indicate that emissions of isoprene oxidation products from plants increase with abiotic stress and may be associated with lipid peroxidation at high temperatures. The results suggest that isoprene is an important ecosystem antioxidant involved in signaling processes through the formation of reactive electrophile species. These observations highlight the need to investigate further the mechanisms of isoprene oxidation in plants under stress and its biological and atmospheric significance.

Reference: Jardine, K. J., K. Meyers, L. Abrell, E. G. Alves, A. M. Yanez Serrano, J.  Kesselmeier, T. Karl, A. Guenther, J. Q. Chambers, and C. Vickers. 2013. “Emissions of Putative Isoprene Oxidation Products from Mango Branches Under Abiotic Stress,” Journal of Experimental Botany 64(12), 3669-79. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 18, 2013

Improving Estimates of Soil Organic Carbon Stored in Permafrost

Recent research has revealed that the amount of soil organic carbon (SOC) stored in the northern circumpolar permafrost region is far larger than earlier estimates, calling attention to the potential vulnerability of this carbon for release to the atmosphere. Even so, these new estimates of the quantity, decomposability, and combustibility of permafrost-region SOC stocks are poorly constrained, contributing to large uncertainties in model predictions of carbon–climate feedbacks under future warming. Two workshops held at Argonne National Laboratory during 2011 and 2012 led to a synthesis of the current differences between empirical and model estimates of the size and distribution of permafrost-region SOC stocks, and research needs to reduce this discrepancy were identified. Five research challenges for improving empirical assessments of the distribution and potential mineralization of SOC stocks in the northern permafrost region were highlighted. These include (1) improving the number and robustness of observations, (2) predicting the spatial and vertical distributions of SOC stocks, (3) characterizing existing carbon forms to better predict their fate, (4) using improved observation-based SOC estimates to inform model development, and (5) quantifying uncertainties in observations and predictions. These challenges are interlinked and suggest opportunities to organize, prioritize, and coordinate future research efforts to better understand and predict the impacts of permafrost SOC.

Reference: Mishra, U., J. D. Jastrow, R. Matamala, G. Hugelius, C. D. Koven, J. W. Harden, C. L. Ping, G. J. Michaelson, Z. Fan, R. M. Miller, A. D. McGuire, C. Tarnocai, P. Kuhry, W. J. Riley, K. Schaefer, E. A. G. Schuur, M. T. Jorgenson, and L. D. Hinzman. 2013. “Empirical Estimates to Reduce Modeling Uncertainties of Soil Organic Carbon in Permafrost Regions: A Review of Recent Progress and Remaining Challenges,” Environmental Research Letters 8, 035020. DOI:10.1088/1748-9326/8/3/035020. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 01, 2013

Evaluating the CO2 Component of Climate Models Using ARM Southern Great Plains Site Data

Aircraft data collected over the Southern Great Plains (SGP) site were used to analyze changes in the three-dimensional (3D) distribution of atmospheric CO2 for several greenhouse gas concentration trajectories adopted by the Intergovernmental Panel on Climate Change for its fifth Assessment Report. Using the Community Earth System Model–Biogeochemistry (CESM1-BGC), scientists first compared CO2 concentrations simulated for 1850 to 2005 to surface, aircraft, and column observations. Second, the evolution of spatial and temporal gradients within the SGP’s 3D observational footprint during the twenty-first century was examined. By upscaling the results, the study showed that the mean annual cycle in atmospheric CO2 was underestimated for the historical period throughout the Northern Hemisphere, suggesting that the growing season net CO2 flux in the Community Land Model (the land component of CESM) was too weak. Over the last half century, the growth rate of atmospheric CO2 was higher in the model than in observations, suggesting that the overall sensitivity of land and ocean CO2 uptake to rising atmospheric CO2 (and other human global change perturbations) was too weak (i.e., model parameterization of the land and ocean to rising CO2 needs to be adjusted) . The diagnostics that were developed in this paper provide a means to test future generations of coupled carbon–climate models.

Reference: Keppel-Aleks, G., J. T. Randerson, K. Lindsay, B. B. Stephens, J. K. Moore, S. C. Doney, P. E. Thornton, N. M. Mahowald, F. M. Hoffman, C. Sweeney, P. P. Tans, P. O. Wennberg, and S. C. Wofsy. 2013. “Atmospheric Carbon Dioxide Variability in the Community Earth System Model: Evaluation and Transient Dynamics during the Twentieth and Twenty-First Centuries,” Journal of Climate 26, 4447–75. DOI: 10.1175/JCLI-D-12-00589.1. (Reference link)

Contact: Wanda Ferrell, SC-23.1, (301) 903-0043, Rickey Petty, SC-23.1, (301) 903-5548, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 15, 2013

Improving Carbon Fluxes in Earth System Models

The extreme complexity of earth system models (ESMs) is necessary to represent the many processes underlying terrestrial carbon cycle processes. However, simple models may be useful to qualitatively understand projected dynamic responses to warming and to identify processes missing in the models. A U.S. Department of Energy scientist at Lawrence Berkeley National Laboratory developed a simple model for vegetation carbon response by tracking the movement of the most statistically similar climate at every location in an ESM over past time and recalculating the carbon flux within the Fifth Climate Model Intercomparison Project (CMIP5) ESMs. The most important area of disagreement between this simple method and the full ESM calculations are in the southern boreal forest, where ESMs project carbon gains, while the simplified approach projects carbon losses. This finding suggests that potential carbon losses such as forest disturbance and mortality, known to be missing in the ESMs, need to be better represented to robustly predict the carbon response in this region.

Reference: Koven, C. 2013. “Boreal Carbon Loss Due to Poleward Shift in Low-Carbon Ecosystems,” Nature Geoscience, accepted.

Contact: Dorothy Koch, SC-23.1, (301) 903-0105
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 25, 2013

Forest Water Use and Water-Use Efficiency at Two FACE Sites

Predicted responses of transpiration to elevated atmospheric CO2 concentrations are highly variable among process-based models. To better understand and constrain this variability, forest carbon and water flux data from the free-air CO2 enrichment (FACE) experiments at Duke University and Oak Ridge National Laboratory were compared to simulations from 11 ecosystem models. A primary objective was to identify key underlying assumptions in model structure that cause differences in model predictions of transpiration and canopy water-use efficiency. Model-to-model and model-to-observations differences resulted from four key sets of assumptions: (1) the nature of the stomatal response to elevated CO2; (2) the roles of the leaf and atmospheric boundary layer; (3) the treatment of canopy interception; and (4) the impact of soil moisture stress. The degree of coupling between carbon and water fluxes, and how that coupling is calculated, is one of the key assumptions that determines how well the models compare with observations. This study yields a framework for analyzing and interpreting model predictions of transpiration responses to elevated CO2. This approach highlights key areas for immediate model improvement, hypotheses for experimental testing, and opportunities for data synthesis to significantly reduce discrepancies among models.

Reference: Kauwe, M. G., B. E. Medlyn, S. Zaehle, A. P. Walker, M. C. Dietze, T. Hickler, A. K. Jain, Y. Luo, W. J. Parton, C. Prentice, B. Smith, P. E. Thornton, S. Wang, Y. P. Wang, D. Wårlind, E. S. Weng, K. Y. Crous, D. S. Ellsworth, P. J. Hanson, H. Seok-Kim, J. M. Warren, R. Oren, and R. J. Norby. 2013. “Forest Water Use and Water Use Efficiency at Elevated CO2: A Model-Data Intercomparison at Two Contrasting Temperate Forest FACE Sites,” Global Change Biology, DOI: 10.1111/gcb.12164. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 20, 2013

Soil Feedbacks to the Climate System

A key question in Earth system science is: Will warming lead to increased soil organic matter decay and an accelerated release of soil carbon as CO2? If yes, a self-reinforcing feedback would result with warming begetting warming. In 1991, a replicated, in situ soil-warming experiment was established at the Harvard Forest in central Massachusetts to address this question. Rates of CO2 production have been measured monthly for microbial and root respiration from April through November. Initially, warmed plots had higher respiration than controls, but after about a decade, the warming-accelerated CO2 production decreased and returned to background levels. However, during the last seven years of the study (years 16–22), soil respiration again increased in the heated plots relative to the control plots – a long-term response to soil warming never before documented. Based on measurements made over the first 15 years that showed the depletion of the soil’s labile carbon pool, the investigators hypothesized that much of the carbon respired over the last seven years has come from the recalcitrant soil carbon pool. Using 13C compound-specific soil incubation studies, they found that long-term soil warming increases the microbial carbon-use efficiency (CUE) associated with the degradation of complex (recalcitrant) carbon compounds such as phenol, but that the CUE of simple carbon compounds such as glucose was not temperature sensitive. Additional preliminary data shows a shift in microbial community structure in the heated plots that indicates an increase in taxa or pathways adapted to recalcitrant carbon decomposition. This long-term study suggests that the soil microbial community will adapt to long-term warming in a way that will lead to a depletion of the recalcitrant soil carbon stocks and a self-reinforcing feedback to the climate system.

Reference: Frey, S. D., J. Lee, J. M. Melillo, J. Six. 2013. “Soil Carbon Cycling: The Temperature Response of Soil Microbial Efficiency and Its Feedback to Climate,” Nature Climate Change 3, 395–98. DOI: 10.1038/nclimate1796. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 23, 2012

Steve Wofsy (Harvard University) will be awarded the 2012 Roger Revelle Medal at this year's American Geophysical Union meeting

The Revelle Medal is awarded to an individual "for outstanding contributions in atmospheric sciences, atmosphere-ocean coupling, atmosphere-land coupling, biogeochemical cycles, climate, or related aspects of the Earth system." Wofsy is being recognized for a distinguished career in the factors that regulate atmospheric composition, including experimental field studies of the carbon cycle using long-term eddy-covariance measurements of atmosphere-biosphere exchange in tropical, boreal, and midlatitude forests. Wofsy is currently supported by BER's Terrestrial Ecosystem Science program and is working on land-biosphere interactions (biogenic volatile organic compound and trace gas emissions) in Brazil. Wofsy was also an organizer for the Next-Generation Ecosystem Experiment: Tropics workshop held in Bethesda, Md., in June 2012.

References: Roger Revelle Medal (Reference link)
Steve Wofsy (Reference link)

Contact: Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


June 27, 2012

Uncertainty Quantification Framework Applied to Community Land Model Reveals Uncertainty in Model Hydrology

Many aspects of land hydrology in climate models are uncertain and important for correctly simulating climate and cloud changes. A new, more precise system of estimating land model uncertainties has been designed and implemented in the Community Land Model (CLM4) by U.S. Department of Energy scientists at Pacific Northwest National Laboratory and Oak Ridge National Laboratory. They analyzed the sensitivity of simulated surface heat and energy fluxes to selected hydrologic parameters in CLM4 by applying a new method of uncertainty quantification (UQ) to 13 Ameriflux tower sites that span a wide range of climate conditions and provide measurements of surface water, energy, and carbon fluxes. UQ is used to select the most influential CLM parameters for increased focus and research. The results suggest that the CLM4 simulated latent/sensible heat fluxes show the largest sensitivity to parameters associated with subsurface runoff. This work is the first UQ study on the CLM4 and has demonstrated that uncertainties in hydrologic parameters could have significant impacts on the simulated water and energy fluxes and land surface states, which will in turn affect atmospheric processes and the carbon cycle.

Reference: Hou, Z., M. Huang, L. R. Leung, G. Lin, and D. M. Ricciuto. 2012. “Sensitivity of Surface Flux Simulations to Hydrologic Parameters Based on an Uncertainty Quantification Framework Applied to the Community Land Model,” Journal of Geophysical Research Atmospheres, DOI: 10.1029/2012JD017521. (Reference link)

Contact: Dorothy Koch, SC-23.1, (301) 903-0105
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 16, 2011

Deforestation Drives Cooling at Mid- to High Latitudes

Deforestation in mid- to high latitudes is hypothesized to have the potential to cool the Earth's surface by altering biophysical processes. When continental-scale land clearing is included in climate models, cooling is triggered by increases in surface albedo and is reinforced by a land albedo-sea ice feedback. This feedback is a key component of the model predictions; without it other processes overwhelm the albedo effect to generate warming. Ongoing activities, such as land management for climate mitigation, are occurring at local scales (hectares) presumably too small to generate the feedback. It is not known if the intrinsic biophysical mechanism on its own can consistently change surface temperatures. The effect of deforestation on climate has also not been demonstrated over large areas from direct observations. Now, DOE researchers show that surface air temperature is lower in open land than in nearby forested land. The effect is 0.85°±0.44K (mean ± one standard deviation) north of 45°N (essentially north of the U.S.-Canadian border) and 0.21°±0.53K southwards. Below 35°N (south of Tennessee, all of Texas and New Mexico, and southern California), there is weak evidence that deforestation leads to warming. Results are based on temperature comparisons at forested eddy covariance towers in the United States and Canada and, as a proxy for small areas of cleared land, nearby surface weather stations. Night-time temperature changes unrelated to changes in surface albedo are also an important contributor to the overall cooling effect. The observed latitudinal dependence is consistent with theoretical expectations of changes in energy loss from convection and radiation across latitudes in both the daytime and night-time phase of the diurnal cycle, the latter of which remains uncertain in climate models.

Reference: Lee, X., M. L. Goulden, D. Y. Hollinger, A. Barr, T. A. Black, G. Bohrer, R. Bracho, B. Drake, A. Goldstein, L. Gu, G. Katul, T. Kolb, B. E. Law, H. Margolis, T. Meyers, R. Monson, W. Munger, R. Oren, K. T. Paw, A. D. Richardson, H. P. Schmid, R. Stabler, S. Wofsy, and L. Zhao. 2011. “Observed Increase in Local Cooling Effect of Deforestation at Higher Latitudes,” Nature 479, 384-87. DOI: 10.1038/nature10588. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 02, 2011

Forest Soil Carbon Lost at a Greater Rate in Warmer Climates

Understanding and predicting the impacts of climate change and the stability of carbon stored in terrestrial ecosystems is an important part of planning future energy strategies. This Oak Ridge National Laboratory-led study compared the turnover time of labile soil carbon, in relation to temperature and soil texture, in several forest ecosystems that are representative of large areas of North America. Carbon (C) and nitrogen (N) stocks and C:N ratios were measured in the forest floor, mineral soil, and two mineral soil fractions (particulate and mineral-associated organic matter) at five AmeriFlux sites (a network that provides continuous observations of ecosystem-level exchanges of CO2, water, and energy across the Americas) along a latitudinal gradient in the eastern United States. With one exception, forest floor and mineral soil carbon stocks increased from warm, southern sites (with fine-textured soils) to cool, northern sites (with more coarse-textured soils). The exception was a northern site, with less than 10% silt-clay content, that had a soil organic carbon stock similar to the southern sites. Moving from south to north, the turnover time of labile soil organic C increased from approximately 5 to 14 years. Consistent with its role in stabilization of soil organic carbon, silt-clay content was positively correlated with stable C at each site. Latitudinal differences in the storage and turnover of soil C were related to mean annual temperature, but soil texture superseded temperature when there was too little silt and clay to stabilize labile soil C and protect it from decomposition. Overall, this study suggests that large labile pools of forest soil C are at risk of decomposition in a warming climate, especially in coarse textured forest soils.

Reference: Garten, C. T., Jr. 2011. "Comparison of Forest Soil Carbon Dynamics at Five Sites along a Latitudinal Gradient," Geoderma 167-168, 30-40, DOI: 10.1016/j.geoderma.2011.08.007. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 29, 2011

Global Rates of Photosynthesis Greater than Previously Assumed

Estimates of global carbon sinks have large uncertainties that complicate estimates of Earth's capacity to buffer rising atmospheric carbon dioxide (CO2). Photosynthesis is a major contributor to these carbon sinks. A DOE-funded team led by Ralph Keeling at the Scripps Institution of Oceanography followed the path of oxygen atoms on CO2 molecules during photosynthesis to create a new way to measure the efficiency of the world's plants. The ratio of two natural isotopes of oxygen in CO2 told researchers how long the CO2 had been in the atmosphere and how fast it had passed through plants. From this, they estimated that the global rate of photosynthesis is about 25 percent faster than thought. This new approach linked the changes in oxygen isotopes to El Niño, the global climate phenomenon associated with a variety of unusual weather patterns including low rainfall in tropical regions of Asia and South America. The naturally occurring isotopes of oxygen, 18O and 16O, are present in different proportions in the water inside leaves during dry, El Niño periods in the tropics. This oxygen ratio in leaf waters is passed along to CO2 when CO2 mixes with water inside leaves. This exchange of oxygen between CO2 and plant water also occurs in regions outside of the tropics that are not as affected by El Niño and where the 18O/16O ratio is more "normal." The team measured the time it took for the global 18O/16O ratio to return to normal following an El Niño event to infer the speed at which photosynthesis is taking place. They discovered that the ratio returned to normal faster than expected indicating that global photosynthesis occurs at a greater rate than previously assumed. The rate, expressed in terms of how much carbon is processed by plants in a year, has now been revised upward from the previous estimate of 120 Pg of carbon a year to a new annual rate between 150-175 Pg. These results suggest that the uncertainty in estimating global carbon sinks is even greater than previously thought.

Reference: Welp, L. R., R. F. Keeling, H. A. J. Meijer, A. F. Bollenbacher, S. C. Piper, K. Yoshimura, R. J. Francey, C. E. Allison, and M. Wahlen. 2011. "Interannual Variability in the Oxygen Isotopes of Atmospheric CO2 Driven by El Niño," Nature 477, 579-82. DOI:10.1038/nature10421. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 01, 2011

Elevated CO2 and O3 Alter Soil Organic Matter Cycling in Northern Deciduous Forests

Over time, changes in plant growth and litter production caused by rising CO2 and O3 concentrations could impact the storage and cycling of carbon in soil organic matter. DOE’s decade-long investment in a multi-factor Free-Air CO2 Enrichment (FACE) experiment in Rhinelander, Wisconsin, enabled scientists from Argonne National Laboratory and two Midwest universities to observe that elevated CO2 changed the trajectories of three soil organic matter pools characterized by extent of decomposition. As the experiment progressed, relatively undecomposed particulate organic matter fragments built up more rapidly in the soil of plots exposed to elevated CO2, while the amount of carbon found in more highly processed mineral-associated organic matter pools declined under elevated CO2 but not in ambient soils. Thus, elevated CO2 appears to have increased the cycling of carbon and nitrogen in the soil organic matter of the sandy soils at this site. In contrast, elevated O3 tended to have the opposite effect, reducing both detritus inputs and the cycling of soil carbon and nitrogen. The effects of O3 occurred regardless of atmospheric CO2 concentration. Although forest community composition altered the magnitude of the responses, enhanced turnover of soil organic matter could limit the potential for long-term soil carbon sequestration in the northern deciduous forests of an elevated CO2 world.

References: Hofmockel, K. S., D. R. Zak, K. K. Moran, and J. D. Jastrow. 2011. "Changes in Forest Soil Organic Matter Pools After a Decade of Elevated CO2 and O3," Soil Biology and Biochemistry 43, 1518-1527.

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 28, 2011

Declining Soil Nitrogen in a Free Air CO2-Enrichment Experiment (FACE)

The sustainability of higher ecosystem production under elevated atmospheric carbon dioxide (CO,2) is unknown. Nitrogen (N) is often limited in ecosystems as a result of N incorporation into long-lived biomass and soil organic matter. As a result, N limitation could eventually limit or nullify increasing forest productivity under elevated CO2 (i.e., “Progressive N Limitation”). In the first six years of the Oak Ridge National Laboratory (ORNL) FACE experiment, there was no apparent evidence that N limitation was exacerbated by elevated CO2 or that N limitation reduced sweetgum tree growth. However, the CO2 stimulation of sweetgum tree growth has more recently declined and was tentatively attributed to N limitation. Using stable N isotopes, temporal trends in sweetgum leaf litterfall 15N abundance provided strong evidence that N availability in the ORNL FACE plots has in fact declined over time, and declined faster in plots exposed to elevated CO2, providing evidence for progressive N limitation. Although these results cannot be generalized for other FACE sites, examination of leaf litterfall d15N may provide an accurate indicator of soil N availability and progressive N limitation.

References: Garten Jr., C. T., C. M. Iversen, and R. J. Norby. 2011. “Litterfall 15N Abundance Indicates Declining Soil Nitrogen Availability in a Free Air CO2 Enrichment Experiment,” Ecology 92, 133–39 [doi:10.1890/10-0293.1].

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 18, 2011

Changing Water Balance in Forests Exposed to Elevated CO2

Plants influence ecosystem water balance through responses to environmental conditions, and their sensitivity to climate change could alter the ecohydrology of future forests. DOE scientists at Oak Ridge National Laboratory used a combination of measurements, synthesis of existing literature, and modeling to study the consequences of elevated CO2 on ecohydrologic processes in forests. Data from five of DOE’s free-air CO2 enrichment (FACE) sites reveal that elevated CO2 reduced the passage of water vapor through the stomata, or small pores of the plant, leading to declines in canopy transpiration and water use for three closed-canopy forest sites. At the sweetgum FACE experiment in Oak Ridge, Tennessee, elevated CO2 reduced seasonal transpiration by 10–16%. Model simulations also predicted reduced demand for water in response to elevated CO2. The direct effect of elevated CO2 on forest water balance through reductions in transpiration could be considerable, especially following canopy closure and development of maximal leaf area index. Complementary, indirect effects of elevated CO2 include potential increases in root or leaf litter and soil organic matter, shifts in root distribution and altered patterns of water extraction.

References: Warren, J. M., E. Pötzelsberger, S. D. Wullschleger, P. E. Thornton, H. Hasenauer, and R. J. Norby. 2011. “Ecohydrologic Impact of Reduced Stomatal Conductance in Forests Exposed to Elevated CO2,” Ecohydrology 4, 196–210. DOI: 10.1002/eco.173.

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 21, 2011

Carbon Release from Roots to Microbes Prevents Nitrogen Limitation Under CO2 Enrichment

A forest’s ability to store carbon depends on resource limitations, such as nitrogen. The Progressive Nitrogen Limitation (PNL) theory suggests that under elevated CO2, a forest will immobilize nitrogen in biomass, limiting nitrogen needed for enhanced growth. DOE scientists show, for the first time, that mature trees exposed to CO2 enrichment increase the release of soluble carbon from roots to soil, and that such increases are coupled to the accelerated turnover of nitrogen pools in the rhizosphere. Over the course of three years, the team measured in situ rates of root exudation from intact loblolly pine (Pinus taeda L.) roots at the Duke Forest, near Chapel Hill, North Carolina. Trees fumigated with elevated CO2 increased exudation rates by 55% during the primary growing season, leading to a 50% annual increase in dissolved organic inputs to fumigated forest soils. These increases in root-derived carbon were positively correlated with microbial release of extracellular enzymes involved in breakdown of organic nitrogen in the rhizosphere, indicating that exudation stimulated microbial activity and accelerated the rate of soil organic matter turnover. Trees exposed to both elevated CO2 and nitrogen fertilization did not increase exudation rates and had reduced enzyme activities in the rhizosphere. These results provide field-based empirical support suggesting that sustained growth responses of forests to elevated CO2 in low fertility soils are maintained by enhanced rates of microbial activity and nitrogen cycling fuelled by inputs of root-derived carbon. However, the decomposition of soil organic matter by the stimulated microbes may prevent a large soil carbon pool from accumulating in forest soils.

References: Phillips, R. P, A. C. Finzi, and E. S. Bernhardt. 2011. “Enhanced Root Exudation Induces Microbial Feedbacks to N Cycling in a Pine Forest Under Long-Term CO2 Fumigation,” Ecology Letters 14, 187–94.

Drake, J. E, A. Gallet-Budynek, K. S. Hofmockel, E. S. Bernhardt, S. A. Billings, R. B. Jackson, K. S. Johnsen, J. Lichter, H. R. McCarthy, M. L. McCormack, D. J. P. Moore, R. Oren, S. Palmroth, R. P. Phillips, J. S. Pippen, S. G. Pritchard, K. K. Treseder, W. H. Schlesinger, E. H. DeLucia, and A. C. Finzi. 2011. “Increases in the Flux of Carbon Belowground Stimulate Nitrogen Uptake and Sustain the Long-Term Enhancement of Forest Productivity Under Elevated CO2,” Ecology Letters 14, 349–57.

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 22, 2011

Improving Our Understanding of Carbon Fluxes in Diverse Ecosystems

AmeriFlux is a long-term carbon dioxide measuring and monitoring network to help define the global carbon dioxide budget, improve predictions of future carbon dioxide concentrations, and enhance understanding of net ecosystem productivity and carbon sequestration of the terrestrial biosphere. DOE scientists studied key environmental and meteorological drivers from different vegetation types at 56 AmeriFlux sites that influence their ability to measure the fluxes of carbon dioxide. Using 305 site years worth of data and a statistical analysis of the cluster differences, the authors identified light intensity, vegetation type, and water vapor as key factors that impact the pattern and magnitude of the turbulent exchange. These results will improve our ability to measure and model carbon dioxide fluxes in diverse ecosystems.

Reference: Schmidt, A., C. Hanson, J. Kathilankal, and B. E. Law. 2011. “Classification and Assessment of Turbulent Fluxes above Ecosystems in North America with Self-Organizing Feature Map Networks,” Agricultural and Forest Meteorology 151, 508–20.

Contact: Daniel Stover, SC-23.1, (301) 903-0289, Mike Kuperberg, SC-23.1, (301) 903-3281
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 22, 2011

New Approach for Predicting Ecosystem Responses to Global Change

Long-term ecological responses to global change are strongly regulated by slow processes, such as changes in species composition, carbon dynamics in soil and long-lived plants, and accumulation of nutrient capitals. Understanding and predicting these processes require experiments on decadal time scales. But even decadal experiments may not be adequate because many of the slow processes have time scales much longer than those experiments. DOE-funded scientists have proposed a new, coordinated research approach that combines long-term, large-scale global change experiments with process studies and modeling. They propose that long-term global change manipulative experiments, especially in high-priority ecosystems such as tropical forests and high-latitude regions, be conducted in tandem with complementary process studies (e.g., using model ecosystems, species replacements, laboratory incubations, isotope tracers, and greenhouse facilities) to best inform long- and short-term responses. This new, coordinated approach that combines long-term experiments, process studies, and modeling has the potential to be the most effective strategy for gaining information on long-term ecosystem dynamics in response to global change.

Reference: Luo, Y., J. Melillo, S. Niu, C. Beier, J. S. Clarks, A. T. Classen, E. Davidson, J. S. Dukes, R. D. Evans, C. B. Field, C. J. Czimczik, M. Keller, B. A. Kimball, L. M. Kueppers, R. J. Norby, S. L. Pelini, E. Pendall, E. Rastetter, J. Six, M Smith, M. G. Tjoelker, and M. S. Torn. 2011. “Coordinated Approaches To Quantify Long-Term Ecosystem Dynamics in Response to Global Change,” Global Change Biology 17, 843–54.

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 25, 2010

AmeriFlux Contributes New Insights into Evapotranspiration

Large scale changes in the Earth's water cycle have been hypothesized to result from global warming. DOE-funded investigators and DOE's AmeriFlux network report in Nature evidence of systematic changes in global land evapotranspiration, although the authors are not able to assign causality to the changes. Using a combination of long-term observational (including data from numerous AmeriFlux sites), meteorological and remote sensing records, combined with model results, the authors identify a systematic increase in global land evapotranspiration from 1982 to 1997. From 1998 to 2008, this trend appears to have declined or leveled off. The authors suggest that soil moisture limitations, particularly in the southern hemisphere are responsible for the change. If this continues over the long-term, it may indicate that climate-driven changes in terrestrial hydrological cycles exist and that there are limits to the ability of these cycles to respond to changing climate.

Reference: Jung, M., M. Reichstein, P. Ciais, S. Seneviratne, J. Sheffield, M. Goulden, G. Bonan, A. Cescatti, J. Chen, R. de Jeu, A. J. Dolman, W. Eugster, D. Gerten, D. Gianelle, N. Gobron, J. Heinke, J. Kimball, B. Law, L. Montagnani, Q. Mu, B. Mueller, K. Oleson, D. Papale, A. Richardson, O. Roupsard, S. Running, E. Tomelleri, N. Viovy, U. Weber, C. Williams, E. Wood, S. Zaehle, and K. Zhang. 2010. "Recent Decline in the Global Land Evapotranspiration Trend Due to Limited Moisture Supply," Nature 467, 951–954. DOI: 10.1038/nature09396.(Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 18, 2010

Changing Climate Alters Plant Communities

A long-term ecosystem manipulation study was conducted in an old-field ecosystem on the Oak Ridge Reservation. Temperature, precipitation, and atmospheric carbon dioxide were manipulated over several years. The study found that while precipitation was the dominant factor, all manipulated factors impacted plant productivity and community structure. Plant species differed in their responses to each climate change factor, resulting in changes in the composition of the plant community. Such compositional shifts can alter ecosystem biomass production and nutrient inputs, and are an important part of ecosystem response to climatic change. This study highlights the complexity of understanding ecosystems and their responses to change.

Reference: Kardol, P; C. Campany; L. Souza; R. Norby; J. Weltzin and A. Classen; 2010. "Climate change effects on plant biomass alter dominance patterns and community evenness in an experimental old-field ecosystem," Global Change Biology, 16, 2676–2687, doi: 10.1111/j.1365-2486.2010.02162.x

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 15, 2010

DOE's AmeriFlux Network Improves Understanding of Global Carbon Cycle

A critical uncertainty in the terrestrial carbon cycle is the relationship between incoming solar radiation and the productivity of plants receiving that radiation. Data was collected from 35 carbon flux measurement sites around the world, including 13 U.S. AmeriFlux sites. By combining carbon flux and supporting biological and meteorological data with NASA satellite data, water availability was shown to have a larger impact on the function of vegetation than other measured physical parameters such as temperature. These results will improve estimates of how plant function is likely to respond to changing climate. The DOE-led multi-agency Ameriflux network provides measurements on the function and carbon cycle of ecosystems that advances understanding of processes regulating carbon assimilation, respiration, and storage, and linkages between carbon, water, energy, and nitrogen through measurements and modeling.

Reference: Martín F. Garbulsky, Josep Peñuelas, Dario Papale, Jonas Ardö, Michael L. Goulden, Gerard Kiely, Andrew D. Richardson, Eyal Rotenberg, Elmar M. Veenendaal and Iolanda Filella; 2010; "Patterns and controls of the variability of radiation use efficiency and primary productivity across terrestrial ecosystems," Global Ecology and Biogeography, 19, 253-267.

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 15, 2010

Elevated CO2 Changes Plant Dynamics in a Forest Ecosystem

DOE has developed and supported a number of long-term Free-Air CO2 Enrichment (FACE) studies to evaluate the response of entire ecosystems to increased CO2 associated with a changing climate. Oak Ridge National Laboratory has managed one of those sites for over 11 years and reports a set of findings in a recent issue of the Journal of Plant Ecology. Over the course of the experiment, the understory plant community changed dramatically. Above ground biomass was ~25% greater in plots exposed to elevated concentrations of carbon dioxide. Early in the study (2001-2003), herbaceous species made up 94% of the total understory biomass. After multiple years of treatments (2008), woody shrubs and saplings comprised 39% of total understory biomass in plots not receiving additional CO2 treatments and 67% in plots receiving elevated CO2 treatments. Understory communities in plots receiving elevated CO2 treatments also showed more rapid transition from herbaceous to woody-dominated communities, indicating faster succession. These results suggest that rising atmospheric CO2 concentration could accelerate ecosystem succession and have long-term impacts on forest dynamics.

References: Souza L, Belote RT, Kardol P, Weltzin JF, Norby RJ (2010) "CO2 enrichment accelerates successional development of an understory plant community," Journal of Plant Ecology 3(1): 33-39.

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 01, 2010

Limitations to Modeling Heterogeneous Landscapes in Climate Research

Characterizing the carbon balance and heat fluxes in heterogeneous landscapes is difficult, yet critical to understand present and future climate-land surface interactions, including ecosystem feedbacks to climatic change. A recent DOE study investigated modeling approaches, using three years of high quality measurements, to characterize land-atmosphere interactions in the very heterogeneous U.S. southern Great Plains. The modeling approach used in current land-surface models led to discrepancies in the regional carbon balance of up to 50% (weekly total) and 20% (annual total). Discrepancies in predicted weekly average regional latent heat fluxes were smaller but also existed for spatial and diurnal predictions. In this heterogeneous system, more rigorous characterization of spatial variation of land surface properties than that used in present models is needed to make accurate regional simulations.

Citation: Riley WJ, Biraud SC, Torn MS, Fischer ML, Billesbach DP, Berry JA (2009) Regional CO2 and latent heat surface fluxes in the Southern Great Plains: Measurements, modeling, and scaling. J. Geophys. Res. - Biogeosciences 114 Article Number: G04009

Contact: Jeffrey S. Amthor, SC-23.1, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


January 11, 2010

New Insights Into Climate Change and Mortality in Western Forests

Drought causes significant tree mortality at the regional and global scales, but it is difficult to predict likely effects of ongoing and future climatic changes on tree mortality because the relationships between climate and mortality remain unclear. Recently published DOE-sponsored research examined relationships between tree-climate interactions and mortality of ponderosa pine in northern New Mexico. Ponderosa pine is widely distributed in North America, ranging from central Mexico to southern Canada, and may be representative of a large group of tree species. The study results indicate that trees from drier areas (i.e., growing under long-term water-limited conditions) were predisposed to mortality caused by an acute drought event, which is an unexpected result. Because increased drought severity and frequency are projected for many mid-latitude regions, it appears possible that forest mortality events will increase in the drier regions of the western United States in the coming decades.

Reference: McDowell NG, Allen CD, Marshall L (2010) Growth, carbon-isotope discrimination, and drought-associated mortality across a Pinus ponderosa elevational transect. Global Change Biology 16:399-415.

Contact: Jeffrey S. Amthor, SC-23.1, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


November 02, 2009

Tree Mortality and Insights from a Decade of Climate Change Research

Ongoing global climatic change is expected to result in longer and more frequent droughts. Recent drought in the western United States has been associated with widespread mortality of pine trees, but because the mechanism of action has been unclear it has been impossible to realistically account for such mortality in global climate models. Now, after 10 years of DOE-sponsored research, it has been determined that long-term drought reduces photosynthesis (carbon assimilation) in pine trees to such an extent that they become "carbon starved." As a result, they are not able to ward off other stresses, such as attack by bark beetles. This new insight into the mechanism of action of drought on tree health will allow global climate models to appropriately account for potential ecological effects of climatic change.

Reference: Breshears, D.B., Myers O.B., Meyer, C.W., Barnes, F.J., Zou, C.B., Allen, C.D., McDowell, N.G., Pockman, W.T.. (2009) Tree die-off in response to global change-type drought: mortality insights from a decade of plant water potential measurements. Frontiers in Ecology and the Environment 7:185-189.

Contact: Jeffrey S. Amthor, SC-23.1, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


October 19, 2009

Adding another Century to the Central European Temperature Record by Removing Early Instrumental Warm-Bias - A Windfall for Global Change Research

Preindustrial surface air temperature records contain biases that make their use for global change research difficult. Understanding and removing those biases would give scientists access to records prior to 1850, broadening current temperature records to a multi-centennial scale. DOE-funded scientist Phil Jones (University of East Anglia in Norwich, UK) and his colleagues have succeeded in creating an instrumental temperature record for the Greater Alpine Region (GAR) in central Europe beginning in the year 1760 by accounting for changes in how instruments were inadequately protected from direct sunlight prior to 1850-1870, when new screening procedures were put in place. Lack of adequate protection caused temperatures in the summer to be biased warm and those in the winter to be biased cold. Removal of those systematic errors was the key to creating this valuable, new, expanded data resource. The results also have broader implications for the calibration of historical proxy climatic data in the region such as tree ring indices and documentation of grape harvest dates.

Reference: Böhm, R., P. D. Jones, J. Hiebl, D. Frank, M. Brunetti, and M. Maugeri. 2009. "The Early Instrumental Warm-Bias: A Solution for Long Central European Temperature Series, 1760-2007," Climatic Change 101(1–2), 41–67. DOI: 10.1007/s10584-009-9649-4. (Reference link)

Contact: Anjuli Bamzai, SC-23.1, (301) 903-0294, Renu Joseph, SC-23.1, (301) 903-9237
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


April 06, 2009

Climate-Relevant Isoprene Chemical Pathways Uncovered

In spite of their many positive attributes, including removing carbon from the atmosphere, some trees also contribute to the challenges of climate change. Many deciduous trees emit isoprene (2-methyl-1,3-butadiene, C5H8) during daylight hours, a major organic carbon compound  accounting for up to 2% of the carbon fixed by those plants and about one third of total volatile organic compounds (VOC) emissions. DOE research has previously demonstrated that isoprene oxidation may contribute significantly to the global aerosol burden with impacts on climate forcing and ozone production. A recent study by this same group described isoprene photooxidation and developed a detailed mechanism, including branching ratios and yields, for the compounds identified. The authors summarize the most important features of this mechanism in a scheme appropriate for use in global chemical transport models. The impact of this chemistry is important in the light of the potential for significant changes in isoprene emissions caused by climate change  and changes in land use.

Reference: F. Paulot, J. D. Crounse, H. G. Kjaergaard, J. H. Kroll, J. H. Seinfeld, and P. O. Wennberg (2009), Isoprene photooxidation: new insights into the production of acids and organic nitrates, Atmos. Chem. Phys., 9, 1479-1501.

Contact: Ashley Williamson, SC-23.1, (301) 903-3120
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


March 16, 2009

Estimating Fossil Energy-based CO2 Emissions from U.S. Croplands

DOE supports research to understand mechanisms of carbon sequestration in managed ecosystems. An important part of that research is knowing the sources of carbon emissions. Scientists from Oak Ridge National Laboratory report a method to estimate both on- and off-site fossil energy-based CO2 emissions (FCE) associated with crop production. FCE was found to differ by crop and region because of changes in energy requirements for crop production driven by environmental differences (e.g., soil texture, soil chemistry, and climate). Changes in policies (e.g., farm bills) and abrupt changes in annual weather patterns (e.g., droughts and wet years) have also resulted in annual shifts in FCE. This new method is important because estimates of fossil-fuel consumption for cropping practices and the associated CO2 emissions enable (1) monitoring of energy and emissions with changes in land management and (2) calculation and balancing of regional and national carbon budgets.

Reference:  Nelson, R.G., C.M. Hellwinckel, C.C. Brandt, T.O. West, D.G. De La Torre Ugarte, G. Marland. 2009. Energy Use and Carbon Dioxide Emissions from Cropland Production in the United States, 1990-2004. Journal of Environmental Quality 38: 418-425.

Contact: Mike Kuperberg, SC-23.1, (301) 903-3511; Roger Dahlman, SC-23.1, (301) 903-4951
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


February 23, 2009

DOE Terrestrial Carbon Researcher Named Georgia Regents' Professor

Professor Monique Leclerc, of the University of Georgia's Crop and Soil Sciences Department, has been named a State of Georgia Regents' Professor. Regents' Professors are faculty members whose scholarship or creative activity is recognized both nationally and internationally as innovative and pace-setting. Regents' Professors receive a permanent increase in salary and a yearly academic support account for the duration of the professorship. Professor Leclerc is an investigator in DOE's terrestrial carbon program, studying the role of vegetation-atmosphere exchange of gases such as carbon dioxide, water, and sulfur dioxide in climate change. This exchange of gases is regulated by a number of factors, including source-sink strengths of those gases and the structure of the turbulent flow within the vegetation canopy.

Contact: Mike Kuperberg/Roger Dahlman, SC-23.1, (301) 903-3511 / (301) 903-4951
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


December 08, 2008

Novel Relationship Between Nitrogen and Albedo (Solar Radiation Reflectance) in Forests

A positive correlation between the uptake of nitrogen and carbon by leaves has been recognized for some time. However, in a study published this week in the Proceedings of the National Academy of Sciences, scientists report that this relationship also holds for whole forest canopies and that both variables are strongly related to canopy albedo (the fraction of solar radiation that is reflected). This suggests that nitrogen levels in forests can influence Earth's climate in ways that have not previously been recognized. The article reports that forests with high levels of foliar nitrogen reflect more solar radiation and absorb more CO2 than forest with lower nitrogen levels. They also discovered that variation in forest canopy nitrogen can be accurately detected using satellites, making it possible to continuously track these global-scale effects of forests on the Earth's climate system. Significant data for these analyses was provided by DOE-funded AmeriFlux sites.

Reference:  S.V. Ollinger, A.D. Richardson, M.E. Martin, D.Y. Hollinger, S. Frolking, P. B. Reich, L.C. Plourde, G.G. Katul, J.W. Munger, R. Oren, M-L. Smith, K.T. Paw U, P. V. Bolstad, B.D. Cook, M.C. Day, T.A. Martin, R.K. Monson, and H.P. Schmid (2008) Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks. ww.pnas.org/cgi/doi/10.1073/pnas.0810021105

Contact: Mike Kuperberg/Jeff Amthor/Roger Dahlman, SC-23.1, (301) 903-3281
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


September 15, 2008

New, Surprising Insights into Potential Effects of Ozone Pollution on Forest Growth

Fossil fuel use is causing an increase in the concentrations of both carbon dioxide and ozone in the atmosphere. The increasing carbon dioxide concentration is expected to stimulate tree growth, while available data indicate that increasing ozone can counteract the beneficial effects of increasing carbon dioxide on tree growth. Recently published measurements from the longest running field experiment exposing trees to elevated carbon dioxide and ozone, research sponsored by DOE, surprisingly indicate that the combination of elevated carbon dioxide and ozone stimulated root growth in some tree communities. The scientists conducting the research suggested that the death of ozone-sensitive trees followed by increased growth of ozone-tolerant trees made possible by access to space and soil nutrients that would have been used by ozone-sensitive trees might be the explanation for the increased root growth. But whatever the mechanism might be, these new results indicate a possible long term response to increasing concentrations of carbon dioxide and ozone that is not generally considered in assessments of potential effects of the changing composition of the atmosphere on forest tree growth.

Contact: Jeffrey S. Amthor, SC-23.1, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER


July 21, 2008

The Changing Atmosphere Could Drive Forests to Use More Water

Fossil fuel use is causing an increase in the atmospheric concentrations of both carbon dioxide and ozone. In principle, an increase in the concentration of either gas can reduce the amount of water used by plants in transpiration (evaporation of water from plants), but a group of SC-sponsored scientists recently discovered that this was not the case in a unique and large-scale field experiment. The scientists directly measured effects of elevated carbon dioxide and ozone concentrations on forest-tree transpiration in the SC Program for Ecosystem Research's ecosystem-scale elevated-carbon-dioxide and elevated-ozone field experiment in northern Wisconsin forest stands (the world's largest long-term study of ecological effects of changes in atmospheric composition). They found that increasing the concentration of the gases 40-50% above ambient concentrations caused an increase in transpiration of about 14%. The results indicate that, if other factors remain constant, increasing atmospheric concentrations of carbon dioxide and ozone might cause an increase in water use by temperate forests. These findings alter our basic understanding of interactions between atmospheric composition and water cycling in forests. The research was recently reported in the journal Tree Physiology.

Contact: Jeffrey S. Amthor, SC-23.1, (301) 903-2507
Topic Areas:

Division: SC-23.2 Biological Systems Science Division, BER
      (formerly SC-23.1 Life Sciences Division, OBER)


July 21, 2008

University of Tennessee Field Day Includes DOEs Program on Carbon Sequestration in Terrestrial Ecosystems (CSiTE)

The University of Tennessee is holding its 2008 Field Day on July 24, 2008, with 19 different tours being offered. Three of this years tours will include the production of switchgrass, bioenergy, and storage of carbon in soils of the switchgrass system. DOEs CSiTE program will participate at the Milan, Tennessee, site. CSiTE is a joint Laboratory Program that investigates properties and processes of terrestrial carbon sequestration. A part of their field research is carried out at the Milan Switchgrass site. The Field Day draws visitors from around the country, and over 3,000 visitors attended previous events. Chuck Garten and Robin Graham of ORNL will present results on CSiTE research, discussing how switchgrass production as a feedstock for biofuel can provide a double dividend, since it also increases soil carbon sequestration, reducing the rate of CO2 increase in the atmosphere.

Contact: Roger C. Dahlman, SC-23.1, (301) 903-4951
Topic Areas:

Division: SC-23.2 Biological Systems Science Division, BER
      (formerly SC-23.1 Life Sciences Division, OBER)


July 21, 2008

Will Changes in Atmospheric Composition Caused by Fossil Fuel use Affect Pulpwood Quality?

Fossil fuel use is causing an increase in the concentrations of both carbon dioxide and ozone in the atmosphere. Both gases can affect the physiology of trees, so they might affect the quality of wood grown for pulp, i.e., tree stems grown principally to make wood pulp used in paper production and for some other wood products such as oriented strand board. Trees grown as part of the SC Program for Ecosystem Research's large-scale elevated-carbon-dioxide and elevated-ozone ecosystem experiment in northern Wisconsin provide a unique opportunity to experimentally determine whether future increases in carbon dioxide and ozone concentration might affect pulpwood quality. Using those trees, a team of scientists from Europe and the United States determined that the quality of wood from aspen trees was unaffected by elevated carbon dioxide and ozone concentrations, but that increased carbon dioxide and ozone increased the fraction of undesirable "extractives" in paper birch trees. This result indicates the possibility that the byproducts of fossil-fuel use might have a modestly negative effect on the economically important pulpwood industry. The research was reported earlier this year in the international journal Tree Physiology.

Contact: Jeffrey S. Amthor, SC-23.1, (301) 903-2507
Topic Areas:

Division: SC-23.2 Biological Systems Science Division, BER
      (formerly SC-23.1 Life Sciences Division, OBER)


April 07, 2008

Dioxide Concentration May Not be All Good News for Crops

It has been widely recognized for decades that the marketable yield of most crops is increased when they are grown in an elevated CO2 concentration, but a recent field experiment found that attack on soybeans by western corn rootworm, and by Japanese beetle, was increased with elevated CO2. A BER-sponsored research project investigating the underlying cause of this increased insect attack in elevated CO2 recently reported (April 1, 2008, Proc. Nat. Acad. Sci.) that elevated CO2 reduced the effectiveness of normal biochemical systems that plants use to help defend themselves against insects. The researchers concluded that changes in the plant’s natural defense systems caused by the ongoing increase in atmospheric CO2 concentration (which is caused mainly by energy production from fossil fuels) has the potential to exacerbate pest problems in crops of the future.

Contact: Jeffrey S. Amthor, SC-23.3, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-23.3 Climate Change Research Division, OBER)


April 07, 2008

Increased Cold Damage to Plants With Warmer Springs?

Plant ecologists have long been concerned that global warming (caused in large part by energy production from fossil fuels) may actually increase the risk of plant frost damage. The underlying hypothesis is that mild winters and warm, early springs, which are expected to occur as warming continues, may induce "premature" leaf growth in many ecosystems, resulting in exposure of young leaves to subsequent late-spring frosts. The 2007 spring freeze in the eastern United States provided an excellent opportunity to evaluate this hypothesis and assess its potential consequences. A group of BER-sponsored researchers at Oak Ridge National Laboratory (collaborating with NASA, NOAA, and university scientists) analyzed the course of events over a period of early spring leaf growth, caused by unusually warm conditions, followed by a dramatic (and unusual) regional-scale late-spring freeze. The freeze resulted in regional-scale leaf damage and death, with extensive defoliation at many locations, which was observed from the ground and in satellite data. The researchers concluded that the possibility of future increased fluctuations in spring temperatures pose a real threat to some plants in temperate climates. The results were published in the March issue of BioScience.

Contact: Jeffrey S. Amthor, SC-23.3, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-23.3 Climate Change Research Division, OBER)


May 01, 2006

Influence of Climate Change on Plant Respiration and Carbon Storage

Results of a modeling study by scientists at Oak Ridge National Laboratory show that acclimation of plant respiration to changing temperature would affect the amount of carbon stored in terrestrial plants in a potentially warmer climate of the future. The amount of carbon stored in terrestrial plants in a warmer climate will depend, in part, on the effect of increasing temperature on the respiration of plant leaves. Past carbon cycle models predict a positive feedback on global warming through increased plant and soil respiration and less carbon storage in terrestrial plants. However, results of the ORNL modeling study show that if terrestrial carbon cycle models include acclimation of plant maintenance respiration to warming, the positive feedback effect on global warming is reduced compared to that predicted if there was no acclimation of the respiration.

Contact: Roger Dahlman, SC 23.3, (301) 903-4951
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-23.3 Climate Change Research Division, OBER)


May 01, 2006

Mountain Snow Pack Projected to Decline

A global climate model with an embedded downscaling scheme predicts that regional mean mountain snow pack would decline by up to 50-80% for many regions of the globe over the next century in response to a scenario of increasing greenhouse gas concentrations in the atmosphere. Previous studies with regional climate models have suggested similar reductions for selected regions and decades in the 21st century. Now, for the first time, a global climate model provides global estimates of snowmelt with 5 km spatial resolution for the period 1980-2100. Researchers at the Pacific Northwest National Laboratory added a physically-based downscaling scheme to the Community Climate System Model (CCSM), and used the model to simulate the climate for the period 1980-2100 using an Intergovernmental Panel on Climate Change scenario of increasing greenhouse gas concentrations during this period as a climate forcing. The downscaling scheme used was fully interactive with the atmosphere and land components of the CCSM and provided global 5 km spatial resolution for any climate variable. Snow pack is most sensitive to spatial resolution because of its dependence on both temperature and precipitation, both of which also depend on surface elevation.

Reference: Ghan, S. J., and T. Shippert. 2006. "Physically-based global downscaling: Climate change projections for a full century," J. Climate 19 15891604.

Contact: Anjuli Bamzai, SC-23.3, (301) 903-0294
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-23.3 Climate Change Research Division, OBER)


April 18, 2005

Poster Presentation at the Capital on Carbon Sequestration Research

Selected through a National Competition sponsored by the Council on Undergraduate Research, research results on Carbon and Nitrogen Sequestration following Afforestation of Agricultural Soils was presented at a poster session in the Rayburn Office Building. At the Capital event April 19, Bradley University (Peoria, Illinois) undergraduate student, Nathan Mellor, and Professor Sherri Morris, discussed results on interactive effects of forest species, soil chemistry and overall ecosystem processes on soil carbon storage as forests are grown on formerly agricultural soils. An isotope tracer study also determined carbon mineralization rates of different forest systems. The project is providing effective training of young scientists while producing sound scientific information on carbon sequestration by terrestrial ecosystems.

Contact: Roger Dahlman, SC 23.3, (301) 903 4951
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-23.3 Climate Change Research Division, OBER)


March 21, 2005

Office of Science Program Manager Co-Authors Book on Global Change

Biological and Environmental Research (BER) program manager Dr. Jeff Amthor co-authored a recently published book entitled Crops and Environmental Change: An Introduction to Effects of Global Warming, Increasing Atmospheric CO2 and O3 Concentrations, and Soil Salinization on Crop Physiology and Yield. The book published by Haworth Press was written with Prof. Seth Pritchard of the College of Charleston (South Carolina). It provides an in-depth look at the effects, both positive and negative, of climatic change, air pollution, and soil salinization on major crops, including major implications for future crop production and national and global food supply. Prepublication reviewers of the book were enthusiastic. Before joining the BER staff in 2002, Dr. Amthor held research positions at Oak Ridge National Laboratory, Lawrence Livermore National Laboratory, the Department of Agriculture, the University of California (Davis), and Yale University.

Contact: Jeff Amthor, SC-74, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


February 21, 2005

Previous Experimental Studies of Effects of Atmospheric Carbon Dioxide Concentration on Ecosystems Called into Question

A study just published in Nature, supported by the Canadian Government, the U. S. Department of Energy, and the U. S. National Science Foundation, raises important questions about past scientific research on the ecological effects of changes in atmospheric carbon dioxide (CO2) concentration. The result adds a significant wrinkle to, and may even call into question, decades worth of past research on effects of elevated CO2 concentration on plants and ecosystems. In the past, scientists typically exposed plants and ecosystems to present ambient (350 to 370 ppm) and elevated (550 to 750 ppm) CO2 levels, with the elevated level imposed instantaneously (a step-change increase). On the contrary, the CO2 increase in the Earths actual atmosphere is occurring gradually (roughly 1-2 ppm per year), and it is possible that ecosystems will respond differently to a gradual CO2 increase than they do to a step-change increase. This possibility has finally been experimentally tested by John Klironomos (University of Guelph), Mike Allen (University of California, Riverside), Matthias Rillig (University of Montana), and their colleagues. These scientists discovered that a more gradual increase in CO2 concentration, carried out over 21 generations of a model plant-soil system, resulted in different effects than an instantaneous increase in CO2 concentration maintained over the same 21 generations. In particular, the step-change increase resulted in significant perturbations to microorganisms living in the soil, while the gradual increase did not.

Contact: Jeff Amthor, SC-74, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


December 27, 2004

Long-term Ecosystem Research Highlights Fate of Nitrogen in Rainfall

Department of Energy studies on Walker Branch Watershed in the Departments Oak Ridge (Tennessee) National Environmental Research Park showed that stream ecosystems can help prevent nitrogen pollutants from reaching downstream lakes, estuaries, and the ocean. Fossil fuel use is increasing the amount of nitrogen in rainfall in many parts of the United States, and inputs of this nitrogen to aquatic ecosystems can result in harmful algal blooms and drinking water contamination. Combining computer simulation and data from 12 years of field measurements, scientists at Oak Ridge National Laboratory found that biological organisms in streams removed about 20% of the nitrate nitrogen entering the stream from the watershed, thus reducing the concentration of nitrate exported downstream. The removal of nitrate nitrogen was highly seasonal; it was greatest in autumn (due to uptake by bacteria and fungi growing on newly fallen leaves trapped in the stream) and in early spring (due to high rates of uptake by algae before the stream becomes heavily shaded by new leaves in the deciduous forest overhead). These results are consistent with studies at the Hubbard Brook Experimental Forest (New Hampshire) and elsewhere showing that streams can reduce the downstream transport of nitrate nitrogen, and demonstrate the important role of streams in preventing high nitrate export and the eutrophication of downstream aquatic ecosystems. This study was recently documented in the journal Biogeochemistry.

Contact: Jeff Amthor, SC-74, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


September 20, 2004

World's First Whole-Forest Warming Experiment, Open House

In the summer of 2002, Department of Energy (DOE) initiated construction of the first whole-forest warming (soil and air) experimental facility in a field setting. The project is being conducted by University of Wisconsin scientists, along with outside collaborators from the United States and Canada. The purpose is to study effects of (potential) global warming on the structure and functioning of a boreal black spruce forest in northern Manitoba, Canada. The experimental facility (involving large chambers and sophisticated underground temperature control) is now fully functional, with ecological responses to the warming (5 degrees Celsius above ambient) already apparent, including what appears to be significantly increased production of spruce cones (i.e., tree reproductive potential) in the warmed plots. To commemorate the successful operation of the experimental facility, which is expected to continue for several years, the project held an open house September 11, 2004, at the facility. The open house was attended by several dozen interested persons, including Manitoba Hydro's Environmental Education Specialist, Manitoba's Minister of Conservation, and Assistant Deputy Ministers of the Manitoba government.

Contact: Jeff Amthor, SC-74, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


September 13, 2004

BER-Funded Scientist Receives Presidential Early Career Scientist Award

Dr. Margaret Torn of Lawrence Berkeley National Laboratory was given an "early career scientist award" at a September 9 Forrestal Ceremony that saluted seven exemplary investigators from DOE National Laboratories and collaborating universities. Under Secretary David Garman (representing Secretary Abraham) and Dr. Raymond L. Orbach, Director of the Office of Science, presented the awards. Recipients were also recognized for their achievements at the White House by Dr. John Marberger, the President's Science Advisor. Dr. Torn was specifically recognized for her research on the biogeochemistry and sequestration of carbon in soil. Her results are providing new insights for modeling the carbon cycle and carbon sequestration of terrestrial ecosystems. The unique feature of her research is the use of isotopic carbon and oxygen tracers to identify and understand mechanisms and quantities of carbon transformed from plant material to organic matter storage in soil, which is important information for modeling both the carbon cycle and for determining the fate of excess carbon dioxide from energy emissions. One important finding from the tracer research is that fine roots of pine trees live five times longer than previously thought and the roots decompose slowly, which leads to relatively long residence times of carbon that is sequestered by terrestrial ecosystems. Dr. Torn actively engages other scientists in her field investigations of carbon, and one location of the experiments is the DOE Atmospheric Radiation Measurement (ARM) site in Oklahoma.

Contact: Roger C. Dahlman, SC-74, (301) 903-4951
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


August 16, 2004

DOE Ecological Research Facility Tests Ecosystem Models

A paper to be published in the August issue of Ecological Monographs, authored by nine DOE/Office of Science researchers and 10 of their collaborators from a total of 13 institutions, presents a comprehensive test of the ability of 13 ecosystem models to simulate exchanges of carbon and water between a forest and the atmosphere. The model testing used eight years (1993-2000) of data from DOE's Throughfall Displacement Experiment at the Oak Ridge National Laboratory (an Office of Science ecosystem research facility) and other data collected on the DOE Oak Ridge National Environmental Research Park; this represents the longest experimental dataset used to test the largest number of ecosystem models ever. Models that included more detailed energy balance and carbon metabolism calculations provided consistently better predictions, indicating that the level of detail in the models is important. Most of the models were able to predict carbon and water exchanges relatively well when growing conditions were favorable, but many models failed during periods of drought, which occurred during several years of the study period. The loss of model accuracy with drought indicates that considerable uncertainty may exist with respect to present predictions of ecological effects of climatic change on forest ecosystems. Although a single model was not the best predictor of all important ecological variables, the mean of all model outputs was a robust predictor of the observations, even under drought. This result indicates that multiple models, rather than a single "best" model, may be needed to reliably predict effects of environmental changes on ecosystem carbon and water balances.

Contact: Jeff Amthor, SC-74, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


July 12, 2004

BER-Funded Scientists Receive 2004 Norbert-Gerbier Mumm International Award From the World Meteorological Organization for "Most Outstanding Original Publication of the Year"

Dr. Beverly E. Law from Oregon State University and co-authors funded by BER's Carbon Cycle Research program and/or the European Union's CarboEurope Research Program, received the award for a synthesis paper titled Environmental Controls over Carbon Dioxide and Water Vapor Exchange of Terrestrial Vegetation. Dr. Law received the award on behalf of 33 co-authors at a ceremony at WMO Headquarters in Geneva Switzerland on June 16 that was attended by the Secretary-General of the WMO and the Ambassador of the United States. The scientific paper was recognized as the most outstanding original publication of the year on the influence of meteorology on the physical, natural, or human sciences. The paper is based on a synthesis of data from the application of a micrometeorological method used to measure the flux of energy, water, and trace gases, such as carbon dioxide, between the atmosphere and terrestrial ecosystems. The data synthesis, which resulted from application of the method at 37 different locations in North America and Europe with different vegetation types, demonstrated a robust relationship between carbon uptake and water vapor exchange across all of the vegetation and ecosystem types where fluxes were measured. Dr. Law is the science team leader of the U.S. AmeriFlux Network that is about 60% funded by DOE's Office of Science.

Contact: Roger C. Dahlman, SC-74, (301) 903-4951
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


February 12, 2003

Office of Science Ecological Research Reported in Nature and Science

Results from three long-term, large-scale, field research projects supported by the Department of Energys Office of Science were recently reported in the prestigious international scientific journals Nature and Science. All three projects aim to better understand potential effects of environmental changes caused by energy production on the structure and functioning of terrestrial ecosystems in the United States. The Nature article presented data indicating that the abundance and ecological effects of insects and diseases in northern hardwood forests could be altered by increased carbon dioxide and ozone concentrations in the atmosphere. Both carbon dioxide and ozone concentrations are increasing because of fossil fuel use. One of the Science articles presented unique data from a decade-long soil warming experiment in New England that challenges assumptions made in some climate models about possible effects of warming on the release of carbon from forests and their soils. In particular, the research indicates that warming may not cause extensive carbon losses from some forests. The second Science article reported that changes in rainfall variability, a possible consequence of climatic change, can cause significant changes in the functioning of native grasslands in the Midwest. All three studies are continuing with Office of Science support.

Contact: Jeffrey S. Amthor, SC-74, (301) 903-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


April 03, 2002

U.S. Senator Visits BER Research Project

U.S. Senator Carl Levin (Michigan) spent several hours (on February 21, 2002) with the BER-sponsored research team at Michigan Technological University. The research team is studying effects of rising levels of atmospheric carbon dioxide and ozone, both products of energy production, on northern hardwood forest ecosystems. The project findings have important implications for the structure and functioning of forest ecosystems during the coming decades as both carbon dioxide and ozone levels continue to increase. Since the BER-funded study began in 1998, the researchers have discovered significant differences in how various tree species (aspen, birch, and maple) respond to the two-gas mixture, and even differences between trees of the same species (aspen) but with different genetic makeups. Effects of the treatments have been observed at scales ranging from the molecular level up to the entire forest ecosystem. The project was recently renewed, following a peer review, and the senator complimented the research team, saying, "I'm just here to congratulate you, and I'm grateful you received a grant to continue your work."

Contact: Jeffrey S. Amthor, SC-74, 3-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


March 06, 2002

BER Researchers Highly Cited in Global Warming Science

The Institute for Scientific Information (ISI)--publisher of the popular research tools Current Contents and The Science Citation Index--recently released their list of the "Top 25" scientific papers about global warming published between 1991 and 2000 (see [website]). Their analysis tallied the number of scientific journal articles that cited specific scientific papers about various aspects of global warming, and determined the 25 most-cited papers on the topic. Four of those 25 papers were directly related to BER research, and of the 76 authors of those 25 papers, 25 are or were supported by BER grants and contracts. The author of paper number 12, Jeff Amthor, is presently a BER Program Manager. This list from the ISI is a strong indication that BER is playing an important role in national and international scientific studies of global warming, its causes, and its potential effects on humans, economies, and ecosystems.

Contact: Jeffrey S. Amthor, SC-74, 3-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


February 27, 2002

Wheat Growth Stimulated by High CO2

Arnold Bloom (Department of Vegetable Crops, University of California, Davis) and coworkers published the paper "Nitrogen assimilation and growth of wheat under elevated atmospheric carbon dioxide" in the February 5 issue of the Proceedings of the National Academy of Sciences (99:1730-1735). Bloom et al. grew wheat (the world's major food crop) in elevated atmospheric carbon dioxide, a product of energy production. When wheat was grown in an atmosphere containing twice-ambient carbon dioxide (levels that may be realized later in this century) their growth was stimulated as expected. But the researchers found that the form of nitrogen supplied to the plant roots significantly affected their response to elevated carbon dioxide. When wheat was supplied with ammonium nitrogen, the growth stimulation caused by elevated carbon dioxide was about twice the growth stimulation as when plants were given nitrate nitrogen. Bloom et al. discovered that elevated carbon dioxide inhibited the assimilation of nitrate nitrogen by wheat, but not nitrogen in the ammonium form. This may mean that major changes in fertilizer practices in agriculture will be needed in the future as carbon dioxide levels continue to increase. It may also mean that plants in natural ecosystems that prefer nitrate over ammonium as a nitrogen source, will be at a competitive disadvantage in the future because of inhibition of nitrate uptake due to elevated carbon dioxide. The research is supported by BER.

Contact: Jeffrey S. Amthor, SC-74, 3-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


January 23, 2002

A Global Carbon Cycle Problem Solved

Recently published research supported by the Biological and Environmental Research (BER) program has answered an important question about future changes in atmospheric CO2 concentration. During their normal respiratory metabolism, plants globally release about 10 times as much CO2 into the atmosphere each year as humans do by burning fossil fuels (plants also take up CO2 during photosynthesis, so their respiration does not normally contribute to the ongoing atmospheric CO2 increase). Any changes in normal global plant respiration might therefore affect atmospheric CO2 levels. It has been thought for about a decade that rising CO2 might inhibit plant respiration, and that this would act as an important negative feedback on atmospheric CO2 increase. But recent BER research, and other studies building on the BER-supported foundation, indicates that plant respiration is not directly affected by CO2 concentration. Because of this, no negative feedback on CO2 increase is expected from a slowing of plant respiration, and an important uncertainty concerning the future course of atmospheric CO2 changes has been eliminated.

Contact: Jeffrey S. Amthor, SC-74, 3-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


November 14, 2001

Multiple Methods of Estimating Ecosystem Water Use Evaluated in the Field at Oak Ridge National Laboratory

Evapotranspiration (ET) in terrestrial ecosystems is a critical component of the climate system, and better understanding of controls on, and magnitudes of, ET is needed to improve climate models. A multi-year, multi-method study of ET was conducted in an uneven-aged mixed-species deciduous forest at the DOE National Environmental Research Park at Oak Ridge, TN, by Oak Ridge National Laboratory scientist Dr. Paul Hanson and several of his colleagues. The study will lead to improved understanding of water use by forests, and as a result, improved understanding of Earth's climate systems. Key results of this BER-funded study were published recently in Agricultural and Forest Meteorology.

Contact: Jeff Amthor, SC-74, 3-2507
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)


June 06, 2001

Carbon Sequestration Is Enhanced by CO2 Enrichment and Addition of Nutrients.

A Free-Air-CO2-Enrichment (FACE) experiment with a pine forest reports that addition of nutrients significantly enhances growth and carbon sequestration. In the May 23, 2001, issue of Nature science magazine, Ram Oren, Dave Ellsworth, and colleagues report that the enhanced growth is due to the synergistic effect of elevated CO2 and simultaneous nutrient fertilization of the soil. The growth and sequestration responses of this forest ecosystem were greatest when poorest quality sites received CO2 and nutrient amendments. Forests occupy many sites with low soil fertility in the Southeastern United States, and these FACE experiments provide clues about how they are likely to respond as the atmospheric CO2 increases in future years. The research conducted by Duke University and Brookhaven National Laboratory is providing unique data for a wide range of physiological, biogeochemical and ecosystem responses to CO2, and these results from the combined CO2 and nutrient experiment demonstrate the role of fertility in ecosystem carbon cycle and sequestration processes.

Contact: Roger C Dahlman, SC-74, 3-4951
Topic Areas:

Division: SC-23.1 Climate and Environmental Sciences Division, BER
      (formerly SC-74 Environmental Sciences Division, OBER)