BER Research Highlights

Search Date: December 19, 2018

82 Records match the search term(s):


December 27, 2017

Soil Moisture Mediates the Effects of Heating, Roots, and Depth on Root Litter Decomposition

The Science
To explore the effects of soil depth, warming (+4 deg. C), and roots on the breakdown and decomposition of plant inputs, we followed the fate of isotopically labeled root litter in a Mediterranean grassland ecosystem. A team from Lawrence Berkeley National Laboratory (1) manipulated soil temperature, presence of plants, and depth of inputs, (2) monitored resulting soil temperature and moisture, and (3) measured litter remaining after one and two growing seasons.

The Impact
In this Mediterranean grassland, season, depth, heating, and rhizosphere, all influenced soil moisture, which, in turn, overwhelmingly explained root litter decomposition. In moisture-limited ecosystems such as this one, warming may retard, rather than stimulate, microbial decomposition of soil organic carbon. 

Summary
In a Northern California grassland, plots were subjected to three environmental treatments (heating, control, and plant removal), with 13C-labeled root litter buried in either the A horizon (shallow) or B horizon (deep). At the end of each growing season the 13C remaining in the soil was recovered. In the first growing season, decomposition occurred faster in the B than in the A horizon, the latter having greater moisture limitation. Subsequently, there was almost no further decomposition in the B horizon. After two growing seasons, less than 20% of the added root litter C remained in the A or B horizons of all environmental treatments. Heating did not stimulate decomposition, likely because it exacerbated the moisture limitation. However, while plots without plants dried down more slowly than plots with plants, their decomposition rate was not significantly greater, possibly due to the lack of priming by root exudates.

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

(PI Contact)
Margaret Torn
LBNL, UC Berkeley
mstorn@lbl.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, under Award Number DE-AC02-05CH11231, and the National Natural Science Foundation of China (#31622013).

Publications
Castanha, C., B. Zhu, C. E. H. Pries, K. Georgiou, and M. S. Torn. “The effects of heating, rhizosphere, and depth on root litter decomposition are mediated by soil moisture.” Biogeochemistry, 137(1-2), 267-279 (2018). [DOI:10.1007/s10533-017-0418-6]

Topic Areas:


December 23, 2017

Biological Processes Dominate Seasonality of Remotely-Sensed Canopy Greenness in an Amazon Evergreen Forest

Advancing the biophysical understanding of satellite-detected vegetation seasonality in the tropics.

The Science
Satellite observations of Amazon forests show seasonal and inter-annual variation in canopy greenness, but the underlying biological mechanisms leading to a change in greenness have not been resolved. Here a research team from Brookhaven National Laboratory combined canopy radiative transfer models (RTMs) with field observations of Amazon forest leaf and canopy characteristics to test three hypotheses that could explain seasonality in satellite-observed canopy reflectance: (1) changes in the number of leaves per unit ground area (leaf area index), (2) changes in the fraction of the upper canopy that are leafless, and (3) changes in leaf age. They showed that canopy RTMs driven by these three factors closely matched simulated satellite-observed seasonal patterns, explaining ~70% of variability in a key reflectance-based vegetation index. Leaf area index, leafless crown fraction and leaf age accounted for 1%, 33% and 66% of modeled seasonality.

The Impact
The analysis of canopy-scale biophysics rules out satellite artifacts as being a significant cause of satellite-observed seasonal patterns in greenness at this site and implies that leaf phenology can explain large scale remotely-observed patterns. Their study reconciles current controversies about satellite-detected canopy greenness, and enables more confident use of satellite observations to study climate-phenology relationships in the tropics.

Summary
The average annual cycle (2000-2014) of MODIS satellite observed canopy greenness (i.e., MAIAC EVI minimizes the artifacts from clouds/aerosols and sun-sensor geometry) in a Brazilian Amazon evergreen forest, the Tapajos k67 site, shows strong seasonality. This seasonality is primarily driven by canopy NIR reflectance. Here, the team combined rich, field measurements of leaf and canopy characteristics with a 3-D radiative transfer model (i.e. Forest Light Environment Simulator, FLiES) to interpret MAIAC EVI seasonality. The measurements showed that the comprehensive FLiES model with all phenological input (as “P1+P2+P3”) did a good job at simulating MAIAC EVI and NIR reflectance seasonality. This suggests that biological processes dominate canopy-scale reflectance and greenness seasonality in this tropical forest. Further, the research team did model sensitivity analysis to quantify the relative contribution of each of the three phenological factors including “P1” driven by seasonal change in canopy leaf area index only, “P2” driven by seasonal change in canopy-surface leafless crown fraction alone, and “P3” driven by seasonal change in canopy leaf age demography. Their results suggest that canopy-surface leafless crown fraction and leaf age demography control the seasonality in greenness, they did not observe any direct effect of leaf area index on greenness.

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
SP Serbin, A Rogers, and J Wu in part 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.

Publications
Wu J, H. Kobayashi, S.C. Stark, R. Meng, K. Guan, N.N. Tran, S. Gao, W. Yang, N. Restrepo-Coupe, T. Miura, R.C. Oliviera, A. Rogers, D.G. Dye, B.W. Nelson, S. Serbin, A.R. Huete, and S.R. Saleska. “Biological processes dominate seasonality of remotely sensed canopy greenness in an Amazon evergreen forest.” New Phytologist (2017) Epub ahead of print. [DOI: 10.1111/nph.14939]

Topic Areas:


December 20, 2017

Microtopography Determines Active Layer Depths and Responses to Temperature and Precipitation at the NGEE-Arctic’ Barrow Experimental Observatory sites

Landscape features determine thermal and hydrological responses in polygonal tundra.

The Science
A research team from Lawrence Berkeley Laboratory applied a well-tested three-dimensional coupled biogeochemistry, hydrology, vegetation, and thermal model, called ecosys, to polygonal tundra sites in Alaska to quantify and scale the effects of microtopography on Active Layer Depth (ALD), soil hydrology, and energy exchanges with the atmosphere. They found that interannual variation in ALD was more strongly related to precipitation than air temperature, contrary to what most large-scale models assume. Further, they found excellent spatial scaling results from sub-meter to landscape scales using our modeling approach.

The Impact
The LBNL team demonstrated excellent agreement between predictions and NGEE-Arctic observations of soil temperature and moisture and eddy covariance energy exchanges with the atmosphere. The estimates of the importance of precipitation energy content on thaw depth have important implications for predictions of future thermal, hydrological, and biogeochemical states in the Arctic. Finally, these results imply needed improvements to the DOE E3SM land model (ELMv1-ECA).

Summary
Current ESM land model representations of high-latitude thermal and hydrological states ignore several important processes and representation of sub-grid scale heterogeneity, and therefore predicted interactions with the atmosphere remain uncertain. The LBNL analysis here, which combined fine-scale modeling and comparison to a wide range of NGEE-Arctic measurements, demonstrates a viable approach to representing fine-scale processes and links to landscape scale dynamics. Together these findings challenge widely held assumptions about controls on landscape-scale energy and water budgets, and are motivating their ongoing improvements to the DOE land model (ELMv1-ECA).

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.

Publications
Grant, R.F., Z.A. Mekonnen, W.J. Riley, H.M. Wainwright, D.E. Graham, and M.S. Torn.  “Mathematical Modelling of Arctic Polygonal Tundra with Ecosys: 1. Microtopography Determines How Active Layer Depths Respond to Changes in Temperature and Precipitation.” JGR-Biogeosciences, 122(12), 3161-3173 (2017). [DOI: 10.1002/2017JG004035]

Topic Areas:


December 20, 2017

Microtopography Determines How CO2 and CH4 Exchanges Respond to Temperature and Precipitation at an Arctic Polygonal Tundra Site

Microtopography in polygonal tundra affects CO2 and CH4 emissions, but landscape scaling of polygon types accurately represents landscape-scale gas exchanges with the atmosphere.

The Science
Scientists from Lawrence Berkeley National Laboratory applied a well-tested three-dimensional land model (ecosys) to the NGEE-Arctic Barrow, Alaska polygonal tundra sites to quantify and scale the effects of microtopography on biogeochemistry, hydrology, and plant processes and thereby CO2 and CH4 exchanges with the atmosphere. Much of the spatial and temporal variations in CO2 and CH4 fluxes were driven from topographic effects on water and snow movement. Although small-scale elevation variation causes large spatial variations, their results demonstrated that representing individual polygon type dynamics allowed for accurate predictions of landscape-scale states and gas exchanges with the atmosphere.

The Impact
They demonstrated excellent agreement between model predictions and NGEE-Arctic observations of CH4 and CO2 fluxes and the relevant biogeochemical, hydrological, and thermal controlling processes. Interestingly, the net primary productivity in higher features and CH4 emissions across the landscape increased from 1981 to 2015 were attributed more to precipitation than temperatures increases. Their results highlight needed improvements to the DOE E3SM land model (ELMv1-ECA), which they are actively pursuing.

Summary
Current ESM land model representations of high-latitude biogeochemistry and plant processes in spatially heterogeneous landscapes ignore several important processes and representation. They found a strong control of water and snow movement on biogeochemical dynamics and net primary production that varied by landscape position. The landscape-scale dynamics were also well captured by scaling the various polygon type dynamics. The analysis here demonstrates a viable approach to representing fine-scale processes and links to landscape scales. Together their findings challenge widely held assumptions about controls on landscape-scale energy and water budgets, and are motivating our ongoing improvements to the DOE land model (ELMv1-ECA).

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.

Publications
Grant, R.F., Z.A. Mekonnen, W.J. Riley, B. Arora, and M.S. Torn. “Mathematical Modelling of Arctic Polygonal Tundra with Ecosys: 2. Microtopography Determines How CO2 and CH4 Exchange Responds to Changes in Temperature and Precipitation.” JGR-Biogeosciences, 122 (12), 3174-3187 (2017). [DOI: 10.1002/2017JG004037]

Topic Areas:


December 20, 2017

The Millennial Model: In Search of Measurable Pools and Transformations for Modeling Soil Carbon in the New Century

The Science
Scientists at the Lawrence Berkeley National Laboratory built a new conceptual and numerical model — the Millennial model — that defines soil pools based on measurements. They evaluated how its predictions differ from the widely-used Century model.

The Impact
This is the first model to use measurements of particulate organic matter (POM), aggregation, low molecular weight carbon (LMWC) and mineral-associated organic matter (MAOM) to reflect the latest understanding of biological, chemical and physical transformations in soils.

Summary
Soil organic carbon (SOC) can be defined by measurable chemical and physical pools, such as mineral-associated carbon, carbon physically entrapped in aggregates, dissolved carbon, and fragments of plant detritus. Yet, most soil models use conceptual rather than measurable SOC pools. What would the traditional pool-based soil model look like if it were built today, reflecting the latest understanding of biological, chemical, and physical transformations in soils? A team led by the Lawrence Berkeley National Laboratory propose a new conceptual model—the Millennial model—that defines pools as measurable entities. First, they discussed relevant pool definitions conceptually and in terms of the measurements that can be used to quantify pool size, formation, and destabilization. They then developed a numerical model following the Millennial model conceptual framework to evaluate against the Century model, a widely-used standard for estimating SOC stocks across space and through time. The Millennial model predicts qualitatively similar changes in total SOC in response to single factor perturbations when compared to Century, but different responses to multiple factor perturbations. Furthermore, they reviewed important conceptual and behavioral differences between the Millennial and Century modeling approaches, and the field and lab measurements needed to constrain parameter values. The Millennial model is proposed as a simple but comprehensive framework to model SOC pools and guide measurements for further model development.

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

(PI Contact)
Rose Abramoff
Earth Sciences Division, Lawrence Berkeley National Laboratory
rzabramoff@lbl.gov

Funding
The Carbon Cycle Interagency Working Group provided funding for the “Celebrating the 2015 International Decade of Soil — Understanding Soil's Resilience and Vulnerability,” workshop held at the University Corporation for Atmospheric Research in Boulder, CO, USA on March 14-16, 2016. The University Corporation for Atmospheric Research provided meeting space. Lawrence Berkeley National Laboratory is managed and operated by the Regents of the University of California under contract DE-AC02-05CH11231 with the U.S. Department of Energy. Oak Ridge National Laboratory is managed by the University of Tennessee-Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. Department of Energy. Argonne National Laboratory is managed by University of Chicago Argonne, LLC, under contract DE-AC02-06CH11357 with the US Department of Energy.

Publications
Abramoff, R.Z., X. Xu, M. Hartman, S. O’Brien, W. Feng, E.A. Davidson, A.C. Finzi, D. Moorhead, J. Schimel, M.S. Torn, M.A. Mayes, “The Millennial Model: In Search of Measurable Pools and Transformations for Modeling Soil Carbon in the New Century.” Biogeochemistry (2017). [DOI:10.1007/s10533-017-0409-7]

Related Links
https://github.com/email-clm/Millennial

Topic Areas:


November 27, 2017

Soil Carbon Cycle Confidence and Uncertainty

Developing a testbed for global soil carbon modeling.

The Science
Soils represent the largest terrestrial carbon pool on Earth. Yet emerging theories regarding stabilization of soil organic matter remain poorly represented in global-scale models; thus, underestimating the true uncertainty associated with potential terrestrial carbon cycle - climate feedbacks.

The Impact
This work builds the capacity to test emerging ecological theories in global-scale models, informs future research needs, and affords avenues to test soil biogeochemical theory, refine model features, and accelerate advancements across scientific disciplines.

Summary
Models presented in this work are some of the first to begin explicitly considering biotic activity in global-scale biogeochemical models. By forcing them under a common land model, these results are some of the first to begin quantifying the uncertainty associated with potential soil carbon responses to changes in plant productivity, temperature, and moisture and global scales. Notably, the models made divergent projections about the fate of these soil carbon stocks over the 20th century, with models either gaining or losing over 20 Pg C globally between 1901 and 2010.

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

(PI Contact)
Will Wieder
University of Colorado, Boulder
wwieder@ucar.edu

Funding
This work was supported by the US Department of Energy, Office of Science, Biological and Environmental Research (BER) under award numbers: TES DE-SC0014374, BSS DE-SC0016364, Environmental Research, RUBISCO SFA. As well as support from the US Department of Agriculture NIFA 2015-67003- 23485 and National Oceanic and Atmospheric Administration, U.S. Department of Commerce. NA14OAR4320106.

Publications
Wieder, W.R., et al. “Carbon cycle confidence and uncertainty: Exploring variation among soil biogeochemical models.” Global Change Biology (2017). [DOI: 10.1111/gcb.13979]

Related Links
Source code is available at github.com/wwieder/biogeochem_testbed_1.0.

Topic Areas:


November 24, 2017

Anaerobic Microsites have an Unaccounted Role in Soil Carbon Stabilization

Anaerobic microsites within soils impart an unrecognized metabolic protection to carbon, creating a carbon sink vulnerable to climate and land-use change.

The Science
Mechanisms controlling soil carbon storage and feedbacks to the climate system remain poorly constrained. Here, a research team a led by Stanford University shows that anaerobic microsites stabilize soil carbon by shifting microbial metabolism to less efficient anaerobic respiration and protecting reduced organic carbon compounds from decomposition.

The Impact
Without recognizing the importance of anaerobic microsites in stabilizing carbon in soils, terrestrial ecosystem models are likely to underestimate the vulnerability of the soil carbon reservoir to disturbance induced by climate or land use change. Further, carbon mitigation strategies based largely on land management can be optimized accordingly to maximize soil storage.

Summary
Soils represent the largest carbon reservoir within terrestrial ecosystems. The mechanisms controlling the amount of carbon stored and its feedback to the climate and Earth system, however, remain poorly resolved. Global land models assume that carbon cycling in upland soils is entirely driven by aerobic respiration; the impact of anaerobic microsites (small oxygen poor sites in the soil) prevalent even within well-drained soils is missed within this framework. Here, they show that anaerobic microsites are important regulators of soil carbon persistence, shifting microbial metabolism to less efficient anaerobic respiration, and selectively protecting otherwise bioavailable, reduced organic compounds such as lipids and waxes from decomposition. Further, shifting from anaerobic to aerobic conditions leads to a 10-fold increase in volume-specific mineralization rate, illustrating the sensitivity of anaerobically protected carbon to disturbance. The vulnerability of anaerobically protected carbon to future climate or land use change thus constitutes a yet unrecognized soil carbon-climate feedback that should be incorporated into terrestrial ecosystem models.

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

(PI Contact)
Scott Fendorf (lead PI)
Stanford University
Email: Fendorf@stanford.edu

Marco Keiluweit
University of Massachusetts Amherst
Email: keiluweit@umass.edu

Funding
This work was supported by the US Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Program (Award Number DE-FG02-13ER65542), and Subsurface Biogeochemistry Program (Award Number DE-SC0016544). A portion of this research was performed using EMSL, a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory.

Publications
Keiluweit M., T. Wanzek, M. Kleber, P. Nico, and S. Fendorf. “Anaerobic microsites have an unaccounted role in soil carbon stabilization.” Nature Communications 8, Article No. 1771 (2017).  [DOI: 10.1038/s41467-017-01406-6]

Related Links
Phys.org Article: Disrupting sensitive soils could make climate change worse, researchers find
Science Daily: Soil researchers quantify an underappreciated factor in carbon release to the atmosphere
Engadget: Unearthing oxygen-starved bacteria might worsen climate change

Topic Areas:


November 22, 2017

Temporal and Spatial Variation in Peatland Carbon Cycling and Implications for Interpreting Responses of an Ecosystem-Scale Warming Experiment

Variability in peatland carbon cycle processes and implications for interpreting warming experiments.

The Science 
Scientists from Oak Ridge National Laboratory examined variability in peatland carbon stocks and fluxes measured over space and time using field measurements and modeling approaches.

The Impact
Peatlands are carbon-rich ecosystems, and while it is common to measure peatland carbon stocks and fluxes, very few studies quantify variability in these measurements over space and time. This variability should be taken into account when interpreting the significance of experimental treatments, such as the warming and elevated CO2 treatments in the SPRUCE experiment.

Summary
A team lead by ORNL is conducting a large-scale, long-term climate change response experiment in an ombrotrophic peat bog in Minnesota to evaluate the effects of warming and elevated CO2 on ecosystem processes using empirical and modeling approaches. To better frame future assessments of peatland responses to climate change, the team characterized and compared spatial vs. temporal variation in measured C cycle processes and their environmental drivers. They have also conducted a sensitivity analysis of a peatland C model to identify how variation in ecosystem parameters contributes to model prediction uncertainty. High spatial variability in C cycle processes resulted in the inability to determine if the bog was a C source or sink, as the 95% confidence interval ranged from a source of 50 g C m-2 yr-1 to a sink of 67 g C m-2 yr-1. Model sensitivity analysis also identified that spatial variation in tree and shrub photosynthesis, allocation characteristics, and maintenance respiration all contributed to large variations in the pretreatment estimates of net C balance. Variation in ecosystem processes can be more thoroughly characterized if more measurements are collected for parameters that are highly variable over space and time, and especially if those measurements encompass environmental gradients that may be driving the spatial and temporal variation (e.g., hummock vs. hollow microtopographies, and wet vs. dry years). Together, the coupled modeling and empirical approaches indicate that variability in C cycle processes and their drivers must be taken into account when interpreting the significance of experimental warming and elevated CO2 treatments.

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

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

Funding
This material is based on work supported by the US Department of Energy, Office of Science, Office of Biological and Environmental Research. Oak Ridge National Laboratory (ORNL) is managed by UT Battelle, LLC, for the US Department of Energy under contract DEAC05-00OR22725. The SPRUCE experiment is a collaborative research effort between ORNL and the USDA Forest Service. The participation of SDS in SPRUCE efforts was funded by the Northern Research Station of the USDA Forest Service. A portion of this work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Publications
Griffiths, N.A., P.J. Hanson, D.M. Ricciuto, C.M. Iversen, A.M. Jensen, A. Malhotra, K.J. McFarlane, R.J. Norby, K. Sargsyan, S.D. Sebestyen, X. Shi, A.P. Walker, E.J. Ward, J.M. Warren, and D.J. Weston. “Temporal and spatial variation in peatland carbon cycling and implications for interpreting responses of an ecosystem-scale warming experiment.” Soil Science Society of America Journal 81, 1668-1688 (2017). [DOI:10.2136/sssaj2016.12.0422]

Related Links
Spruce and Peatland Responses Under Changing Environments project: https://mnspruce.ornl.gov/

Topic Areas:


November 13, 2017

Predicting and Planning for Chronic Climate-Driven Disturbances

Preparing for long-term ecosystem imbalances could help society manage food, water, energy, and other critical resources.

The Science
Climate-driven disturbances such as heat, drought, wildfire, and insect outbreaks are increasing around the globe and are predicted to rapidly accelerate under future environmental conditions. These disturbances affect ecosystems’ abilities to provide food, water resources, energy, and other essential resources and services to society. In a study led by a scientist at the U.S. Department of Energy’s Pacific Northwest National Laboratory, researchers developed a new theory regarding the effects of chronically increasing disturbances on critical ecosystem functions. They applied this theory to potential Earth system model advances that could help address chronic imbalances in ecosystem services.

The Impact
Predicting chronic imbalances in ecosystem services via Earth system models can improve planning to ensure continued provision of services to society. While researchers focused on how drought and rising temperature affect hydrologic services such as streamflow, water yields, and aquifer recharge, the new framework could include additional events that are expected to increase in likelihood, such as floods and storms. It also could extend to different kinds of ecosystems in which disturbances are expected to become more frequent.

Summary
Scientists reviewed evidence of disturbed ecosystem functions, specifically carbon storage and hydrologic services (e.g., water availability for power generation, drinking, and agriculture). From this data, they developed a theory underlying prolonged climate-driven disturbances and their increasing frequency, which could result in chronic imbalances of ecosystem services. Their theory suggested that warming and drought would lead to chronic mortality. With more frequent disturbances, biomass would disappear more rapidly and would not be regained. This imbalance would correspond with an increasing human population—and demand—for ecosystem services.

Researchers proposed that Earth system models address the possible impacts of chronic imbalances when simulating ecosystem services. For example, next-generation models of future ecosystems could account for new conditions and processes without relying on data based only on past behavior.

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

(PNNL Contact)
Nate McDowell
Pacific Northwest National Laboratory
nate.mcdowell@pnnl.gov

Funding
The U.S. Department of Energy Office of Science, Biological and Environmental Research supported this research. NGM, KB, SM, KS, CX, and RSM acknowledge the support of Los Alamos National Laboratory’s Laboratory Directed Research and Development (LDRD) program. NGM acknowledges the support of Pacific Northwest National Laboratory’s LDRD program. RMM acknowledges the support of the National Science Foundation grant WSC-1204787.

Publication
N.G. McDowell, S.T. Michaletz, K.E. Bennett, K.C. Solander, C. Xu, R.M. Maxwell, C.D. Allen, R.S. Middleton, “Predicting Chronic Climate-Driven Disturbances and Their Mitigation,” Trends in Ecology and Evolution 33:15-27. 2018. [DOI: 10.1016/j.tree.2017.10.002]

Related Links
Reference Link

Topic Areas:

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


November 13, 2017

The Power of Traditional Proxies for Measuring the Soil Carbon Cycle

Solid standbys like clay content should not be displaced by new imaging and genetics techniques.

The Science
Near-term land management and policy decisions depend on proxies, which are used as surrogates for soil features and processes and that affect long-term projections of earth system responses to change. In a new paper, soil ecologists from Pacific Northwest National Laboratory review and classify types of complex soil measurements-called proxies  for the purposes of environmental research.

The Impact
Correlative and integrative proxies in soil carbon (C) cycle measurements have continuing importance because they yield significant insight while being simpler, easier, and cheaper to measure than the actual feature being represented. For example, it is easier to measure clay content as an indicator of soil porosity or carbon storage potential, but understanding which feature is being inferred is important to interpreting the research. The thoughtful use of proxies can lead to new hypotheses and experiments to identify causative relationships; not using proxies may result in overweighting of correlations to explain research results and the misrepresentation of mechanisms.

Summary
In the long history of environmental, soil, and climate change sciences, researchers have always needed proxy variables to improve how complex variables and processes are measured and represented. They have used tree ring chronologies to infer past climate conditions, for instance. And both experimentalists and modelers widely use clay content as a proxy for properties such as bulk density, water-holding capacity, and soil organic matter.

Because of the complexity of processes and interactions within soil, measuring soil C dynamics is another case in which proxies are necessary.

In this realm, ecologists often use two types of proxies. Correlative proxies represent soil characteristics that cannot be directly measured. Integrative  proxies aggregate information about multiple soil characteristics into one variable. Both of these proxies are useful for understanding the soil C cycle and are now being used to make predictions of the C fate and persistence under future climate scenarios. Still, the authors point out, both proxies limit data interpretation.

Meanwhile, new advances in imaging and proteomics have added capabilities and variables to studying the soil C cycle. But so far, these methods are often more expensive and more difficult to measure directly.

In this paper, the authors advocate for the thoughtful use of appropriate proxies for predicting the soil C cycle. Proxies, they say, are simpler, easier, and cheaper to measure, and if used wisely, can suggest new hypotheses and relationships for future study.

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

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

Funding
This paper was the product of a working group assembled at a workshop sponsored by the Carbon Cycle Interagency Working Group via the U.S. Carbon Cycle Science Program under the auspices of the U.S. Global Change Research Program, “Celebrating the 2015 International Decade of Soil – Understanding Soil’s Resilience and Vulnerability,” Boulder, CO, March 2016. VLB, BBL, RP, and KD were supported by grants from the U.S. Department of Energy, Office of Science, Biological and Environmental Research as part of the Terrestrial Ecosystem Sciences Program. KL was supported by NSF DEB-1257032. KTB was supported by Linus Pauling Distinguished Postdoctoral Fellowship program, part of the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory.

Publications
V. Bailey, et al. “Soil carbon cycling proxies: Understanding their critical role in predicting climate change feedbacks,” Global Change Biology online (2017). [DOI: 10.1111/gcb.13926]

Topic Areas:

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


November 01, 2017

Electrical and Seismic Response of Saline Permafrost Soil During Freeze-Thaw Transition

The Science
This study demonstrated the mechanical and electrical responses of Arctic saline permafrost during freeze-thaw processes, and suggested large uncertainty when estimating the unfrozen water content using electrical resistivity data.

The Impact
Electrical and seismic signals during freeze thaw cycles of saline permafrost show characteristic changes with differential hysteresis behaviors. The uncertainty associated with unfrozen water content estimation based on electrical resistivity could be large.

Summary
Our study revealed low electrical resistivity and elastic moduli at temperatures down to approximately -10 °C, indicating the presence of a significant amount of unfrozen saline water under the current field conditions. The spectral induced polarization signal showed a systematic shift during the freezing process, affected by concurrent changes of temperature, salinity, and ice formation. An anomalous induced polarization response was first observed during the transient period of supercooling and the onset of ice nucleation. Seismic measurements showed a characteristic maximal attenuation at the temperatures immediately below the freezing point, followed by a decrease with decreasing temperature. The calculated elastic moduli showed a non-hysteric response during the freeze-thaw cycle, which was different from the concurrently measured electrical resistivity response where a differential resistivity signal is observed depending on whether the soil is experiencing freezing or thawing. The differential electrical resistivity signal presents challenges for unfrozen water content estimation based on Archie's law.

Contacts
(BER PM)

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

(PI Contact)
Yuxin Wu
Lawrence Berkeley National Lab
Ywu3@lbl.gov; 5104864793

Funding
The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science. This research is supported through contract number DE-AC0205CH11231 to Lawrence Berkeley National Laboratory.

Publications
Wu, Y., S. Nakagawa, T.J. Kneafsey, B. Dafflon, and S. Hubbard. 2017. “Electrical and Seismic Response of Saline Permafrost During Freeze-Thaw Transition,” Journal of Applied Geophysics, 146,16-26. DOI: 10.1016/j.jappgeo.2017.08.008.

Topic Areas:

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


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


October 31, 2017

Microbial Community-Level Regulation Explains Soil Carbon Responses to Long-Term Litter Manipulations

A generalizable model modification that improves long-term soil carbon predictions.

The Science
Currently, soil carbon models that explicitly represent microbial activity have large biases in predicted carbon stocks and temporal dynamics. Scientists at Lawrence Berkeley National Laboratory have shown that accounting for density-dependent microbial mortality greatly improves predictions against long-term observations, and improves microbial models for inclusion in Earth System Models.  

The Impact
The proposed model modification addresses a long-standing problem in mechanistic models of soil biogeochemistry and improves predictions of soil carbon storage in response to long-term changes in plant productivity. 

Summary
Changes in climate, atmospheric composition, and land use all have the potential to alter plant inputs to soil in ways that impact soil microbial activity. Many microbial models of soil organic carbon (SOC) decomposition have been proposed recently to advance prediction of SOC dynamics. Most of these models, however, exhibit unrealistic oscillatory behavior and their SOC stocks are insensitive to long-term changes in carbon (C) inputs. DOE National Laboratory Scientists diagnosed the source of these problems in four archetypal microbial models and proposed a density-dependent formulation of microbial turnover, motivated by community-level interactions, that limits population sizes and reduces oscillations. They compared model predictions to 24 long-term carbon-input field manipulations and identified key benchmarks. The proposed formulation reproduces soil carbon responses to long-term carbon-input changes and implies greater SOC storage associated with CO2-fertilization-driven increases in carbon inputs over the coming century compared to recent microbial models. This study provides a simple, yet effective, modification to improve microbial models for inclusion in Earth System Models.

Contacts (BER PM)
Daniel 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)

(PI Contact)
Margaret S. Torn
Lawrence Berkeley National Laboratory
mstorn@lbl.gov; 510-495-2223

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
K. Georgiou, R. Z. Abramoff, J. Harte, W. J. Riley and M. S. Torn, “Microbial community-level regulation explains soil carbon responses to long-term litter manipulations.” Nature Communications, 8:1223 (2017). [DOI: 10.1038/s41467-017-01116-z]

Topic Areas:

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


October 30, 2017

An Observational Benchmark and Scaling Theory for Environmental Controls on Soil Decomposition

Global benchmark shows that existing Earth system models underestimate vulnerability of soils to increased temperature.

The Science  
DOE supported researchers combined global maps of productivity, soil carbon, and environment to demonstrate a basic pattern of environmental controls on soil decomposition, which is that soil carbon temperature sensitivity is highest in cold regions. From this, they derived a theory to explain the pattern as an outcome of the scaling of soil freeze-thaw processes in time and depth, and apply the benchmark to existing ESMs and newer land modeling approaches.

The Impact
The study shows via a global benchmark, that existing models systematically underestimate the temperature sensitivity of soil carbon decomposition, and that the solution to this underestimation is to take into account the way in which surface soils freeze.

Summary
The results show that the sensitivity of soil carbon to temperature is highest in cold climates, even for surface rather than permafrost layers, and that this global pattern can most simply be explained as an outcome of the way in which soils experience freeze-thaw processes. The team also show that all existing (CMIP5-era) ESMs systematically underestimate this temperature sensitivity, whereas newer approaches such as the CLM4.5 representation that forms the basis of the E3SM soil biogeochemistry, can match observations. Thus, our approach shows two major impacts: (1) that the single most important relationship that soil models must consider is the physical scaling of freeze and thaw and (2) existing estimates systematically underestimate the long-term temperature sensitivity of surface soil carbon.

Contacts (BER PM)
Renu Joseph
SC-23.1
renu.joseph@science.doe.gov (301-903-9237)

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

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

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

Funding
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. Department of Energy Office of Science.

Publications
Koven, C. D., et al. “Higher Climatological Temperature Sensitivity of Soil Carbon in Cold Than Warm Climates.” Nature Climate Change 7, 817-822 (2017). [DOI: 10.1038/NCLIMATE3421]. (Reference link)

Topic Areas:

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


October 30, 2017

Root and Rhizosphere Bacterial Phosphatase Activity Varies with Tree Species and Soil Phosphorus Availability in Puerto Rico Tropical Forest

Understanding the role of roots and bacteria in the phosphorus cycle

The Science
Phosphorus is an important nutrient for plant growth, but its availability is often limited in tropical forests. While most studies focus on either roots or bacteria, scientists from Oak Ridge National Laboratory studied an important enzyme (phosphatase) in both roots and bacteria, showing that phosphatase release varies with tree species and soil phosphorus availability.

The Impact
Earth System Models poorly represent tropical forests in part due to a lack of data on both the phosphorus cycle and the belowground processes that influence them. The results can be used to improve how models represent the influence that roots and microbes have on the phosphorus cycle in tropical forests.

Summary
Earth System Models simulate the global carbon cycle to predict how our world responds to and changes with perturbations to the carbon cycle. Tropical forests absorb a large amount of carbon in the atmosphere, which makes it important to understand how they grow and are influenced by environmental factors such as phosphorus. Roots and microbes interact to access nutrients and water from the soil environment. In tropical forests, roots and microbes must release phosphatase, an enzyme that breaks down phosphorus locked into organic material.  Plant growth in future climates may be highly influenced by whether plants can release enough phosphatase to continue growing. Scientists from ORNL studied phosphatase activity in roots and bacteria collected from different tree species and soil phosphorus availabilities in tropical forests of Puerto Rico to better understand phosphatase activity. The influence of roots and bacteria on the phosphorus cycle are not usually included in Earth System Models. The study’s results can be used to help improve 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

(PI Contact)
Richard J. Norby
Oak Ridge National Laboratory
Environmental Sciences Division
Climate Change Science Institute
norbyrj@ornl.gov (865-576-5261)

Funding
This research was supported as part of the Next Generation Ecosystem Experiments – Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research.

Publications
K. Cabugao, C. Timm, A. Carrell, J. Childs, T. Lu, D. Pelletier, D. Weston, R. Norby (2017), “Root and rhizosphere bacterial phosphatase activity varies with tree species and soil phosphorus availability in Puerto Rico tropical forest,” Frontiers in Plant Science 8:1834 (2017). [doi: 10.3389/fpls.2017.01834].

Related Links
http://ngee-tropics.lbl.gov

Topic Areas:

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


October 13, 2017

Measuring Photosynthesis via the Glow of Plants

Novel observations suggest a great potential of measuring global gross primary production via solar-induced fluorescence.

The Science
When energized by photons of sunlight, chlorophyll molecules in plant leaves emit a faint red light — Solar-Induced Fluorescence (SIF). SIF originates directly from the core of the photosynthetic machinery and is produced concurrently with carbon fixation. Orbiting Carbon Observatory-2 (OCO-2) is capable of monitoring SIF at high spatial resolution. After validating OCO-2’s SIF measurements against ground measurements, the team related OCO-2 SIF to gross primary production (GPP) estimated from AmeriFlux sites under the OCO-2’s orbital tracks. A significant linear relationship is obtained between these two variables across different vegetation types.

The Impact
Photosynthesis is the foundation of life and civilization on Earth. Yet our current ability to measure photosynthesis at large scales is extremely limited. The team shows that SIF is a direct proxy of photosynthesis and the relationship is consistent across biomes. This research opens up a new direction for photosynthesis observations at multiple scales. It also shows how ground-based observations such as those from AmeriFlux can be integrated with satellite remote sensing to advance photosynthesis research at local, regional, and global scales. 

Summary
Quantifying gross primary production (GPP) remains a major challenge in global carbon cycle research. Space-borne monitoring of solar-induced chlorophyll fluorescence (SIF), an integrative photosynthetic signal of molecular origin, can assist in terrestrial GPP monitoring. However, the extent to which SIF tracks spatiotemporal variations in GPP remains unresolved. Orbiting Carbon Observatory-2 (OCO-2)’s SIF data acquisition and fine spatial resolution permit direct validation against ground and airborne observations. Empirical orthogonal function analysis shows consistent spatiotemporal correspondence between OCO-2 SIF and GPP globally. A linear SIF-GPP relationship is also obtained at eddy-flux sites covering diverse biomes, setting the stage for future investigations of the robustness of such a relationship across more biomes. Our findings support the central importance of high-quality satellite SIF for studying terrestrial carbon cycle dynamics.

Contacts
(BER PM)

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

(PI Contact)
Lianhong Gu
Distinguished Scientist
Oak Ridge National Laboratory, Oak Ridge, TN
lianhong-gu@ornl.gov / 1-865-241-5925

Jeff Wood
Assistant Research Professor
University of Missouri, MO
woodjd@missouri.edu/1-573-883-3295 (PI)

Funding
The U. S. National Aeronautics and Space Administration (NASA); The U. S. Department of Energy Biological and Environmental Research; The Academy of Finland; The European Union.

Publications
Y. Sun et al. 2017. “OCO-2 Advances Photosynthesis Observation from Space via Solar-Induced Chlorophyll Fluorescence,” Science 358, 189. 10.1126/science.aam5747.

Related Links
http://science.sciencemag.org/content/358/6360/eaam5747

Topic Areas:

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


October 12, 2017

Plant Water Potential Improves Prediction of Empirical Stomatal Models

The Science 
A recent study found that current leaf-level empirical models over-predict stomatal conductance during drought conditions and a recently proposed model improves predictions during drought conditions.

The Impact
Including the impairment of soil-to-leaf water transport will improve predictions of stomatal conductance during drought conditions. Many biomes contain a diversity of plant stomatal strategies during water stress.

Summary
Ecosystem models rely on empirical relationships to predict stomatal responses to changing environmental conditions, but these are not well tested during drought conditions. A team from the University of Utah, in conjunction with NGEE-Tropics compiled datasets of stomatal conductance and leaf water potential for 34 woody plant species that span global forest biomes. They tested how well three major stomatal models and a recently proposed model predicted measured stomatal conductance. They found that current models consistently over predicted stomatal conductance during dry conditions whereas the recently proposed model, which includes loss of hydraulic transport capacity, improved predictions compared to current models, particularly during droughts. These results also show that many biomes contain a diversity of plant stomatal strategies during water stress. Such improvements in stomatal simulation will help to predict the response of ecosystems to future climate extremes.

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

Dorothy Koch
SC-23.1
Dorothy.Koch@science.doe.gov

(PI Contact)
William R. L. Anderegg
University of Utah
anderegg@utah.edu

Funding
Funding for this research was provided by NSF DEB EF-1340270 and the Climate Mitigation Initiative at the Princeton Environmental Institute, Princeton University. SL acknowledges financial support from the China Scholarship Council (CSC). VRD acknowledges funding from Ramón y Cajal fellowship (RYC-2012-10970). BTW was supported by the Next Generation Ecosystem Experiments-Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. DJC acknowledges funding from the National Science Centre, Poland (NN309 713340). WRLA was supported in part by NSF DEB 1714972.

Publications

Anderegg, W. R. L., A. Wolf, A. Arango-Velez, B. Choat, D.J. Chmura, S. Jansen, T. Kolb, S. Li, F. Meinzer, P. Pita, V.R. de Dios, J.S. Sperry, B.T. Wolfe, S. Pacala. “Plant water potential improves prediction of empirical stomatal models.” PLoS ONE 12(10), e0185481 (2017). [DOI: 10.1371/journal.pone.0185481

Topic Areas:


October 05, 2017

Networking Science to Improve Soil Organic Matter Management Opportunities

A perspective from the International Soil Carbon Network.

The Science
Soil organic matter (SOM) sustains terrestrial ecosystems, provides food and fiber, and retains the largest pool of actively cycling carbon (C). Over 75% of the soil organic carbon (SOC) in the top meter of soil is directly affected by human land use practices. Large areas with and without intentional management are also being subjected to rapid climate changes, making many reservoirs of SOC in soil vulnerable to losses by decomposition or disturbance.

In order to quantify potential losses of SOC or its sequestration at field, regional, and global scales, members of the International Soil Carbon Network (ISCN) posit that improvements in scientific data, modeling, and communication are necessary. They also suggest that their network could be a platform for integrating the two scientific communities dominating SOM research: one focused on soil science/soil health and the other focused on the terrestrial C cycle /biogeochemistry. Together, these science communities have an opportunity to combine and transform our knowledge, databases, and mathematical frameworks for the benefit of environmental health and humanity.

The Impact
Soil organic matter (SOM) and its main constituent, soil organic carbon (SOC), interact with several aspects of the Earth system and its services to society, including food, fiber, water, energy, cycling of C and nutrients, and biodiversity. It is critical that the scientific community expand its understanding of SOM and SOC so that we can improve the state of soil and ecological sustainability, as well as contribute to climate change mitigation.

Summary
At the global scale, SOM is one of the largest actively cycling C reservoirs, and direct human activities (growing crops, grazing, and forestry practices) impact over 70% of C stocks in the upper meter of soil. The distribution of soils in managed lands follows the distribution of human land use. Overlaying the estimated SOC stocks with human land-use data shows that the majority of near-surface SOC stocks are directly affected by human activities today.

One global initiative to reduce atmospheric CO2 through soil C sequestration has demonstrated that many soils in managed systems could offer an opportunity for climate regulation. And if these gains are applied across all land management plans, there’s an opportunity to offset C emissions from permafrost, or from the combined projected emissions from land use change and agricultural management.

The ISCN posits that there is a need and an opportunity for the scientific community to: 1) better identify datasets to characterize ecosystem and landscape properties, processes, and the mechanisms that dictate SOC storage and stabilization and their vulnerabilities to change; 2) identify, rescue, and disseminate existing datasets; 3) develop platforms for sharing data, models, and management practices for SOC science; and 4) improve the connection between the research communities related to the global C cycle and to soil management.  

Contacts
(BER PM)

Dan Stover
301-903-0289
Daniel.stover@science.doe.gov

(PI Contact)
Ben Bond-Lamberty
PNNL
BondLamberty@pnnl.gov, 301-314-6759

Kathe Todd-Brown
PNNL
katherine.todd-brown@pnnl.gov, 509-371-6547

Funding
BBL was supported by the Office of Science of the U.S. Department of Energy as part of the Terrestrial Ecosystem Sciences Program. KTB was supported by the Linus Pauling Distinguished Postdoctoral Fellowship program at Pacific Northwest National Laboratory.  

Publications
Harden, JW., G. Hugelius, A. Ahlstrom. 2017. “Networking Our Science to Characterize the State, Vulnerabilities, and Management Opportunities of Soil Organic Matter,” Global Change Biology. DOI: 10.1111/gcb.13896

Topic Areas:

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


October 01, 2017

Hydrogenation of Organic Matter as a Terminal Electron Sink Sustains High CO2:CH4 Production Ratios during Anaerobic Decomposition

Environmental metabolomics suggest a mechanism that controls methane production from peatlands.

The Science
In freshwater wetlands such as peatlands, soils become anoxic at the surface and the majority of organic matter is decomposed through microbial consortia that are believed to primarily terminate in methanogenesis or methane (CH4) production. In peat from high latitude Sphagnum-dominated peatlands that are critical to the global carbon cycle, state-of-the-art environmental metabolomics measurements revealed extensive hydrogenation of organic matter which may serve as a predominant mechanism for producing carbon dioxide (CO2) without CH4, thereby explaining why less CH4 is produced relative to CO2 in many northern peatlands.

The Impact
Based on evidence of organic matter hydrogenation in field samples and peat incubations, we hypothesize new pathways for organic matter degradation in peatlands, whereby electrons are deposited to the organic matter itself rather than to CH4. This mechanism has also been observed to reduce CH4 production in the cow rumen. An examination of past research on animal hosts, suggests many parallels between the chemical and microbiological hydrogenation of organic matter between peatlands and the rumen. Because CH4 has a sustained flux warming potential about 45 times higher than that of CO2, mechanisms that alter CH4 production ratios during peat mineralization have important implications for environmental change.

These results highlight the utility of an “environmental metabolomics” approach which takes advantage of analytical chemistry assets at DOE’s Environmental Molecular Sciences Laboratory (EMSL), for identifying microbial processes in organic matter decomposition that have importance in human and animal health as well as in the role of wetlands in environmental change.

Summary
Peatlands store 1/3 of soil organic carbon (SOC). It has been hypothesized that environmental change will increase the amount of CH4 produced from organic matter decomposition. In the inorganic electron acceptor deficient environment of Sphagnum-dominated peatlands, classical models of anaerobic decomposition suggest that peat mineralization should produce CO2 and CH4 in equal quantities, i.e. CO2:CH4 = 1. While this ratio has been observed during anaerobic decomposition in many wetlands or aquatic environments (e.g., landfills, lake sediments, some fens), numerous investigations from Sphagnum-dominated bogs across the globe have found CO2:CH4 to be much greater than 1. A research team from Georgia Tech used cutting-edge metabolomics techniques, which take advantage of advanced analytical chemistry instruments at EMSL, to provide evidence for ubiquitous hydrogenation of diverse unsaturated compounds that serve as organic electron acceptors in peat, thereby providing the necessary electron balance to sustain CO2:CH4 production >1. In contrast to previously proposed mechanisms, our mechanism adds electrons to C-C double bonds in SOC thereby serving as 1) a terminal electron sink, 2) a mechanism for degrading complex unsaturated organic molecules, and 3) a means to alleviate the toxicity of unsaturated aromatic acids. We propose that organic matter hydrogenation is a major mechanism that modulates the amount of methane that is released from peatlands. Our results have important implications for environmental change, because of the divergent greenhouse warming potential of the two important greenhouse gases emitted from peatlands, CH4 and CO2.

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

Paul Bayer
SC-23.1
Paul.bayer@science.doe.gov (301-903-5324)

(PI Contact)
Joel E. Kostka
Georgia Institute of Technology
joel.kostka@biology.gatech.edu

Paul J. Hanson
Oak Ridge National Laboratory
hansonpj@ornl.gov

Funding
Funding was provided by the U.S. Department of Energy under contract #DE-AC05-00OR22725. Work conducted by JEK, JPC, and RMW was supported by contract # DE-SC0012088 and LP-M, CMZ, JKK, and SDB by contract DE-SC0008092 from the Office of Biological and Environmental Research (OBER), Terrestrial Ecosystem Science (TES) Program, under U.S. Department of Energy contract # DE-SC0012088. OBER also funds the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility.

Publications
Wilson, R.M, M.M. Tfaily, and V.I Rich, et al. “Hydrogenation of organic matter as a terminal electron sink sustains high CO2:CH4 production ratios during anaerobic decomposition.” Organic Geochemistry, 112: 22-32 (2017). [DOI: 10.1016/jorggeochem.2017.06.011]

Topic Areas:


September 28, 2017

Evaluating the Community Land Model (CLM4.5) at a Coniferous Forest Site in Northwestern United States using Flux and Carbon-Isotope Measurements

Model ability to simulate the observed energy and carbon fluxes, carbon stocks, and ecosystem response to water stress is investigated.

The Science
Droughts in the western United States are expected to intensify with climate change. Thus, an adequate representation of ecosystem response to water stress in land models is critical for predicting carbon dynamics. The study’s goal was to evaluate the performance of CLM4.5 against observations at an old-growth coniferous forest site in the Pacific Northwest region of the United States (Wind River AmeriFlux site), characterized by a Mediterranean climate that subjects trees to water stress each summer.

The Impact
CLM4.5 was able to reasonably simulate the observations at Wind River after significant calibration of parameters. While most of the adjustments were site-specific, the adjustment of the slope of the leaf stomatal conductance equation aligned with results from other studies at different coniferous forest sites, suggesting that CLM4.5 could benefit from a revised default value. The results also demonstrate that carbon isotopes can expose structural weaknesses in CLM4.5 and provide a key constraint that may guide future model development.

Summary
DOE supported scientists evaluated CLM4.5 against observations at an old-growth coniferous forest site that is subjected to water stress each summer. They found that, after calibration, CLM4.5 was able to reasonably simulate the observed fluxes of energy and carbon, carbon stocks, carbon isotope ratios, and ecosystem response to water stress (response of canopy conductance to atmospheric vapor pressure deficit and soil water content). The calibration of the slope parameter in the Ball-Berry leaf stomatal conductance model aligned with other studies, suggesting that CLM4.5 could benefit from a revised value of 6, rather than the default value of 9, for needle leaf evergreen temperate forests. This study demonstrates that carbon isotope data can be used to constrain stomatal conductance and intrinsic water use efficiency in CLM4.5, as an alternative to eddy covariance flux measurements. It also demonstrates that carbon isotopes can expose structural weaknesses in the model and provide a key constraint that may guide future model development.

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)
James Ehleringer
University of Utah, Department of Biology
jim.ehleringer@utah.edu (801-581-7623)

Funding
This research was supported by the US Department of Energy’s Office of Science, Terrestrial Ecosystem Science Program, under award number DE-SC0010624. BMR and DRB were supported by the US Department of Energy’s Office of Science, Terrestrial Ecosystem Science Program, under award number DE-SC0010625. PET was supported by the US Department of Energy’s Office of Science, Biological and Environmental Research, Accelerated Climate Modeling for Energy project. We acknowledge the Wind River Field Station AmeriFlux site (US-Wrc, PIs: Kenneth Bible, Sonia Wharton) for its data records. Funding for AmeriFlux data resources was provided by the US Department of Energy’s Office of Science. Data and logistical support were also provided by the US Forest Service Pacific Northwest Research Station.

Publications
Duarte, H. F., B.M. Raczka, D.M. Ricciuto, J.C. Lin, C.D. Koven, P.E. Thornton, D.R. Bowling, C.-T. Lai, K.J. Bible, and J.R. Ehleringer. 2017. “Evaluating the Community Land Model (CLM4.5) at a Coniferous Forest Site in Northwestern United States using Flux and Carbon-Isotope Measurements,” Biogeosciences 14, 4315-4340. DOI: 10.5194/bg-14-4315-2017.

Topic Areas:

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


September 23, 2017

Integration of C1 and C2 Metabolism in Trees

C1 Metabolism in Trees

The Science
An oxidative C1 pathway is known to exist in plants where intermediates with a single carbon atom beginning with methanol are oxidized to CO2. Although the flux of carbon through the C1 pathway is thought to be large, its intermediates are difficult to measure and relatively little is known about this potentially ubiquitous and mysterious pathway. In this study, scientists at Lawrence Berkeley National Laboratory (LBNL) evaluated the C1 pathway and its integration with central metabolism using aqueous solutions of 13C-labeled C1 and C2 intermediates delivered to branches of the tropical species Inga edulis via the transpiration stream.

The Impact
The team’s results demonstrate that methanol activates the C1 pathway in plants which provides an alternative carbon source for glycine methylation in photorespiration, enhance CO2 concentrations within chloroplasts, and produce key C2 intermediates (e.g. acetyl-CoA) for central metabolism. Their observations are consistent with previous studies that demonstrated formaldehyde integrates into photorespiration in the mitochondria by providing an alternate source of CH2-THF used for the methylation of serine to glycine. By eliminating the need for a second glycine for the production of CH2-THF with the subsequent loss of CO2 and NH3, the integration of the C1 pathway into photorespiration may convert it from a net loss of carbon to a net gain. By also suppressing photorespiration via the production of CO2 in chloroplasts, our study presents the hypothesis that the integration of C1 pathway into C2/3 metabolism may boost carbon use efficiency and therefore represent an important mechanism by trees under photorespiratory conditions (e.g., high temperature stress). As agricultural crops are known to be high methanol producers, genetic manipulation of the C1 pathway has the potential to improve yields and tolerance to environmental extremes, thereby providing a new tool to the agriculture, bioenergy, and biomanufacturing industries.

Summary
Methanol is highly abundant in the global atmosphere and is known to be tightly connected to plant growth. However, to date, it is assumed that methanol represents a byproduct of the expansion of cell walls during growth processes. Although evidence for the existence of a C1 pathway in plants was first collected over 50 years ago, its intermediates are difficult to measure and relatively little is known about this potentially ubiquitous, yet mysterious biochemical pathway. Previous research by one of the founding fathers of photosynthesis research (Dr. Andrew Benson), for whom this paper is dedicated, found evidence for an important role of methanol in boosting plant photosynthesis, biomass, and productivity. However, this topic remains controversial as subsequent researchers were unable to observe these effects, and the biochemical mechanism(s) remain unclear.

In this paper, scientists from LBNL employed the newly developed technique in their lab termed dynamic 13C-pulse chase to evaluate the potential existence of the complete C1 pathway and its integration with C2/3 metabolism in individual branches of a tropical pioneer species using aqueous solutions of 13C-labeled C1 (methanol, formaldehyde, formic acid) and C2 (acetic acid, glycine) intermediates delivered via the transpiration stream. They confirm that methanol initiates the complete C1 pathway in plants (methanol, formaldehyde, formic acid, carbon dioxide) by providing the first real-time dynamic 13C-labeling data showing their interdependence. The team present novel aspects about the pathway including the rapid interconversion between methanol and formaldehyde, whereas once oxidation to formate occurs, it is quickly oxidized to CO2 within chloroplasts where it can be re-assimilated by photosynthesis. We show for the first time that reassimilation of C1, respiratory, and photorespiratory CO2 is a common mechanism for isoprene biosynthesis; a strong linear dependence of 13C-labeling of isoprene on 13C-labeling of CO2 was observed across all C1 and C2 13C-labeled substrates. Thus, this analysis presents a new method for studying the reassimilation of internal CO2 sources in plants. Finally, the LBNL research team show, for the first time, that methanol and formaldehyde delivery to the transpiration stream leads to a rapid and quantitative conversion of carbon pools used in the biosynthesis of central C2 compounds (acetic acid and acetyl CoA) and therefore represents a new uncharacterized route to the biosynthesis of these key C2 intermediates widely used in cells as precursors for a diverse suite of anabolic (e.g., fatty acid biosynthesis) and catabolic (e.g., mitochondrial respiration) processes.

These observations are consistent with previous studies that demonstrated formaldehyde integrates into photorespiration in mitochondria by providing an alternate source of CH2-THF used for the methylation of serine to glycine. By eliminating the need for a second glycine for the production of CH2-THF with the subsequent loss of CO2 and NH3, the integration of the C1 pathway into photorespiration may convert it from a net loss of carbon to a net gain. By also suppressing photorespiration via the production of CO2 in chloroplasts, our study presents the hypothesis that the integration of C1 pathway into C2/3 metabolism may boost carbon use efficiency during photorespiratory conditions (e.g., high temperature stress). As all agricultural crops have been shown to be high methanol producers, genetic manipulation of the C1 pathway has the potential to improve yields and tolerance to environmental extremes, thereby providing a new tool to the agriculture, bioenergy, and biomanufacturing industries.

Contacts
(BER PM)

Dan Stover
SC-23.1
daniel.stover@science.doe.gov (301-903-0289)

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

Funding
This material is based upon work 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. et al. 2017. “Integration of C1 and C2 Metabolism in Trees,” International Journal of Molecular Sciences, 18, 2045. DOI:10.3390/ijms18102045.


Related Links
http://www.mdpi.com/1422-0067/18/10/2045

Topic Areas:

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


September 21, 2017

A Parsimonious Modular Approach to Building a Mechanistic Belowground Carbon and Nitrogen Model

New microbial model explains observed relationship between heterotrophic respiration and temperature.

The Science
This study developed a new model of microbial soil decomposition that successfully captured the changing relationship between temperature and microbial respiration during the growing season. We showed that the soil microbial response to plant inputs depends on the nitrogen content of the added plant material.

The Impact
We developed a new model for predicting soil response to changes in soil temperature, moisture, plant inputs and stoichiometry. This model is simple and based on well-defined physical and biological properties, and could be developed to model microbial activity at larger scales.

Summary
Microorganisms that grow in the soil, like bacteria and fungi, affect how much carbon resides in the soil and how much is released to the atmosphere as CO2. Mathematical models used to make climate change predictions often struggle to capture the activity of soil microbes in realistic ways. This study uses well-established descriptions of water and temperature effects on soil microbes to predict rate of carbon and nitrogen cycling in the soil. The new model (called the Dual Arrhenius Michaelis-Menten-Microbial Carbon and Nitrogen Physiology, or DAMM-MCNiP), reproduces the changing relationship between temperature and microbial respiration during the growing season. The study also shows using a theoretical addition of root secretions that the microbial response depends on the nitrogen content of the added plant material. This model is simple and based on well-defined physical and biological properties, and could be developed to model microbial activity at larger scales.

Contacts
(BER PM)

Dan Stover
SC-23.1
Daniel.stover@science.energy.gov

(PI Contact)
Adrien Finzi / Rose Abramoff
Boston University / Lawrence Berkeley National Lab
afinzi@bu.edu / rzabramoff@lbl.gov

Funding
U.S. Department of Energy, grants DE-SC0006916, DE-SC0012288, and DE-AC02-05CH11231; the National Science Foundation (DEB 1237491); U.S. Department of Agriculture grant 2014-67003-22073; and the American Association of University Women Doctoral Dissertation Fellowship.

Publications
R.Z. Abramoff, E.A. Davidson, A.C. Finzi. 2017. “A Parsimonious Modular Approach to Building a Mechanistic Belowground Carbon and Nitrogen Model,” JGR Biogeosciences, 122. 10.1002/2017JG003796

Related Links
http://onlinelibrary.wiley.com/doi/10.1002/2017JG003796/abstract

Topic Areas:

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


September 19, 2017

A Zero Power Warming Chamber for Investigating Plant Responses to Rising Temperature

Development, evaluation, and performance of an improved technique for passively warming plants and ecosystems.

The Science
Advances in understanding and model representation of plant and ecosystem responses to rising temperature have typically required temperature manipulation of research plots. In remote or logistically challenging locations, passive warming using solar radiation is often the only viable approach for temperature manipulation. However, current passive warming approaches are only able to elevate mean daily air temperature by about 1.5 degrees Celsius. We have developed an alternative approach to passive warming that uses modulated venting to allow additional warming. The system requires no electrical power for fully autonomous operation. When tested in our research environment, the coastal tundra of northern Alaska, our chambers were able to double the warming achieved by existing approaches.

The Impact
This technical advance allows researchers to study the effect of greater temperature elevations than previously possible using passive (solar radiation) warming. This is particularly relevant for remote and challenging environments, such as the Arctic, that are projected to experience warming that exceeds the 1.5 degrees Celsius limit of current technology by the middle of the century.

Summary
Our Zero Power Warming (ZPW) chamber requires no electrical power for fully autonomous operation. It uses a novel system of internal and external heat exchangers that allow differential actuation of pistons in coupled cylinders to control chamber venting. This enables the ZPW chamber venting to respond to the difference between the external and internal air temperatures, thereby increasing the potential for warming and eliminating the risk of overheating. During the thaw season on the coastal tundra of northern Alaska our ZPW chamber was able to elevate the mean daily air temperature 2.6 °C above ambient, double the warming achieved by an adjacent passively warmed control chamber that lacked our hydraulic system. We describe the construction, evaluation and performance of our ZPW chamber and discuss the impact of potential artefacts associated with the design and its operation on the Arctic tundra. The approach we describe is highly flexible and tunable enabling customization for use in many different environments where significantly greater temperature manipulation than that possible with existing passive warming approaches is desired.

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 (631-344-2948)

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

Publications
Lewin, K.F., A. McMahon, K.S. Ely, S.P. Serbin, A. Rogers. 2017. “A Zero Power Warming Chamber for Investigating Plant Responses to Rising Temperature,” Biogeosciences, 14, 4071-4083. DOI: 10.5194/bg-14-4071-2017.

Topic Areas:

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







September 14, 2017

Synthetic Iron (Hydr)oxide-Glucose Associations in Subsurface Soil: Effects on Decomposability of Mineral Associated Carbon

Soil minerals stabilize highly decomposable compounds like glucose.

The Science
Recent field studies suggest that interactions with soil mineral phases can stabilize otherwise biodegradable organic matter (OM) in soils against microbial decomposition. To directly assess the effect of organo-mineral associations on an easily decomposable substrate (glucose), the research team conducted a series of laboratory incubations with well-characterized minerals (goethite and ferrihydrite) and native soils from three soil depths. Indeed, while free glucose added to soil was completely respired by microbes within 80 days, almost no glucose that had been sorbed to minerals before incorporation into soil was respired (~100% vs 0.4% respectively).

The Impact
1) This study provides direct evidence that even the most chemically labile organic substrates can be protected from microbial decomposition via association with mineral phases (in this case iron (hydro)oxide). 2) These results support the emerging view that molecular structure is not the sole determinant of SOC stability. 3) The efficacy of the laboratory approach demonstrates that we can use microbial respired CO2 as a tracer for OM desorption in soil, creating additional research opportunities.

Summary
Empirical field-based studies have provided indirect evidence of the capacity of soil minerals to stabilize organic carbon in soil.  However, uncertainties remain as to the effect of mineral association on the bioavailability of organic compounds. To assess the impact of mineral association on the decomposition of glucose, an easily respirable organic substrate, a series of laboratory incubations was conducted with soils from 15, 50, and 85 cm. 13C -labeled glucose was added either directly to native soil or sorbed to one of two synthetic iron (hydr)oxides (goethite and ferrihydrite) that differ in crystallinity and affinity for glucose.  This study demonstrates that association with Fe (hydr)oxide minerals effectively reduced decomposition of glucose by ~99.5% relative to the rate of decomposition for free glucose in soil.  These results emphasize the key role of mineral-organic associations in regulating the fluxes of carbon from soils to the atmosphere by enhancing the persistence of soil organic carbon stocks.

Contacts
(BER PM)

Daniel B. Stover
DOE:  Office of BER / CESD
daniel.stover@science.doe.gov
Tel:  301-903-0289
SC-23.1

(PI Contact)
Margaret S. Torn
Lawrence Berkeley National Laboratory  EESA/CESD
email:mstorn@lbl.gov
Tel: 510-495-2223

Funding
This work was supported as part of the Terrestrial Ecosystem Science Program 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.   

Publications
Porras, R.C., C.E. Hicks Pries, M.S. Torn, and P.S. Nico. 2018. “Synthetic Iron (Hydr)Oxide-Glucose Associations in Subsurface Soil: Effects on Decomposability of Mineral Associated Carbon.” Science of The Total Environment, 613-614, pp. 342-351 DOI: 10.1016/j.scitotenv.2017.08.290.

Topic Areas:

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


September 09, 2017

Using Neutron Imaging to Measure and Model Poplar Root Water Extraction After Drought

Linking root water uptake to root traits, and assessing performance of common models.

The Science
Neutron imaging is used to measure soil water movement and water uptake by individual roots in situ.

The Impact
Root water uptake can be linked to characteristic root traits, such as diameter or age. Comparing actual water uptake with modeled water uptake highlights problems with current model assumptions. This work points to the need for new research to understand soil hydraulic properties with and without roots present.

Summary
Knowledge of plant root function is largely based on indirect measurements of bulk soil water or nutrient extraction, which limits modeling of root function in land surface models. Neutron radiography, complementary to X-ray imaging, was used to assess in situ water uptake from newer, finer roots and older, thicker roots of a poplar seedling growing in sand. The smaller diameter roots had greater water uptake per unit surface area than the larger diameter roots, ranging from 0.0027-0.0116 g/cm2 root surface area/h. Model analysis based on root-free soil hydraulic properties indicated unreasonably large water fluxes between the vertical soil layers during the first 16 hours after wetting — suggesting problems with common soil hydraulic or root surface area modeling approaches, and the need to further research and understand the impacts of roots on soil hydraulic properties.

Contacts
(BER PM)

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

Roland Hirsch
Roland.Hirsch@science.doe.gov (301-903-9009)

(PI Contact)
Jeffrey M. Warren
Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory warrenjm@ornl.gov (865-241-3150)

Funding
Laboratory Directed Research and Development Program at Oak Ridge National Laboratory (ORNL); DOE, Office of Science, Office of Biological and Environmental Research, Office of Workforce Development for Teachers and Scientists and Office of Science Graduate Student Research (SCGSR) program; High Flux Isotope Reactor, a DOE Office of Science User Facility operated by ORNL

Publications
Dhiman, I., H. Bilheux, K. DeCarlo, S.L. Painter, L. Santodonato, J.M. Warren. 2017. “Quantifying Root Water Extraction After Drought Recovery Using Sub-mm In Situ Empirical Data,” Plant and Soil. DOI: 10.1007/s11104-017-3408-5.

Topic Areas:

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


September 06, 2017

Coupled Hydrogeophysical Inversion to Estimate Soil Organic Carbon Content in the Arctic Tundra

The Science
We developed and tested a novel inversion scheme that can flexibly use single or multiple datasets, including soil liquid water content, temperature and electrical resistivity tomography (ERT) data to estimate the vertical distribution of organic carbon content and its associated uncertainty in the Arctic tundra. The results show that jointly using multiple datasets helps to better estimate the organic carbon content, especially at the active layer.

The Impact
Quantitative characterization of soil organic carbon content is essential due to its significant impacts on surface-subsurface hydrological-thermal processes and microbial decomposition of organic carbon, which both in turn are important for predicting carbon-climate feedbacks. We present a novel approach to estimate this soil property and its impacts on the hydrological-thermal regime including the freeze-thaw transition in the Arctic tundra based on observations of soil moisture, soil temperature and electrical resistivity data.

Summary
This study developed and tested a novel approach to estimating soil organic carbon content using inverse modeling that can incorporate diverse hydrological, thermal and ERT datasets. In addition, the study permitted exploration of surface-subsurface hydrological-thermal dynamics and spatiotemporal variations associated with freeze-thaw transitions. Given the importance of characterizing organic carbon content as part of ecosystem and climate studies, the typical challenges associated with collecting and analyzing “sufficient” core data to characterize the vertical and horizontal variability of organic carbon associated with a field study site, and the increasing use of electrical resistivity data to characterize vertical, horizontal, and temporal variability in shallow systems, the new inversion approach offers significant potential for improved characterization of organic carbon content over field-relevant conditions and scales. It also offers significant potential for improving our understanding of hydrological-thermal behavior of naturally heterogeneous permafrost systems.

Contacts
(BER PM)

Dan Stover
SC-23.1
daniel.stover@science.doe.gov (301-903-0289)

(PI Contact)
Susan Hubbard
Earth & Environmental Sciences
Phone: 510-486-5266
Fax: 510-486-5686
Email: sshubbard@lbl.gov

Funding
The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science. This NGEE Arctic research is supported through contract number DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory.

Publications
Tran, A. P., B. Dafflon, and S. S. Hubbard. 2017. “Coupled Land Surface-Subsurface Hydrogeophysical Inverse Modeling to Estimate Soil Organic Carbon Content and Explore Associated Hydrological and Thermal Dynamics in the Arctic Tundra”, The Cryosphere, 11(5), 2089-2109. DOI: 10.5194/tc-11-2089-2017.

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





September 05, 2017

A New Approach to Represent Multi-Consumer, Multi-Species Soil Biogeochemical Reactions for Earth System Models

A new kinetics formulation (SUPECA) scales mixed reaction networks.

The Science
Environmental biogeochemistry emerges from microbially-mediated redox reactions in a complex web of consumers and substrates. The two dominant approaches to represent these reactions, Monod and Synthesizing Unit (SU), are unable to scale consistently across complex reaction networks and fail to include substrate limitations, respectively. The authors here extend these approaches (termed SUPECA) to general redox reaction networks to improve terrestrial ecosystem biogeochemical modeling. The authors also applied the SUPECA approach to analyze the soil moisture constraint on soil organic matter decomposition and compared to a benchmark dataset to show our approach accurately represents this constraint across a wide range of soil moisture conditions. The SUPECA approach is being applied in NGEE-Arctic modeling analyses and in DOE’s Earth System Model (E3SM) Land Model (ELM).

The Impact
The authors demonstrate that (1) existing Monod and Synthesizing Unit kinetics are scaling inconsistent; (2) the new SUPECA kinetics rectifies these problems; and (3) that SUPECA is well-suited to trait-based modeling approaches. The authors also show that SUPECA kinetics enables mechanistic modeling of soil moisture effects on organic matter decomposition.

Summary
Soil organic matter decomposition occurs in an extremely complex network of reactions, substrates, and consumers. To address this problem in a manner amenable to land model representation (e.g., E3SM’s ELM), the authors extended the Equilibrium Chemistry Approximation approach to generic biogeochemical networks that include redox reactions (termed the SUPECA (Synthesizing Unit plus ECA) kinetics). The authors demonstrated that SUPECA consistently scales from single Monod type and redox reactions to a reaction network, while the popular dual Monod kinetics and Synthesizing Unit kinetics fail to do so. It is also demonstrated that SUPECA kinetics is superior to dual Monod kinetics in modeling substrate competition in the presence of substrate-mineral interactions. By applying SUPECA to soil organic matter decomposition, the authors showed that soil aggregates have significant impacts and illustrate potential flaws in current ESM land model approaches. The authors are applying the SUPECA approach in NGEE-Arctic modeling analyses and in DOE’s ELM.

Contacts (BER PM)
Daniel Stover and Dorothy Koch
daniel.stover@science.doe.gov (301-903-0289) and Dorothy.Koch@science.doc.gov (301-903-0105)

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

Funding
DE-AC02-05CH11231 as part of NGEE-Arctic project and Accelerated Climate Modeling for Energy (ACME) project.

Publications
Tang, J.-Y. and W.J. Riley. 2017. “SUPECA Kinetics for Scaling Redox Reactions in Networks of Mixed Substrates and Consumers and an Example Application to Aerobic Soil Respiration.” Geosci. Model Dev. 10, 3277-95. 10.5194/gmd-10-3277-2017.

Topic Areas:

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


August 30, 2017

Developing a Molecular Picture of Soil Organic Matter-Mineral Interactions

Quantitative data will help improve land-carbon models.

The Science  
The terrestrial biosphere plays an important role in the global carbon cycle, partly through how strongly organic compounds (i.e., ligands) and soil minerals bind. These binding sites—or interfaces—play an important role in the long-term persistence of soil carbon. In a new Nature Communications paper, researchers from Pacific Northwest National Laboratory found that both carbon chemistry and environmental conditions affect carbon persistence.

The researchers used dynamic force spectroscopy (DFS) to directly measure the strength with which different types of organic carbon binds to soil minerals, and the conditions under which that organic carbon is released.

Unlike previous methods, DFS allows researchers to quantify the energy needed to separate organic molecules from minerals. That allows them to compare specific functional chemical groups and mineral types to better understand when and how carbon is retained in soils or how easily it escapes to the atmosphere.

Changes to soil moisture, such as flooding and drought, change the nano-scale chemical environment (ionic strength and pH) in ways that alter the overall quality of carbon potentially solubilized in natural soils.

The Impact
This approach to obtaining direct and quantitative treatment of the organic–mineral interface could provide fundamental information and critical new measurements that may inform the next generation of process-rich land-carbon models.

Summary
Complex interactions among plants, microbes, and minerals mean soil organic matter (SOM) can reside in soils anywhere from months to millennia. In this study, researchers set out to better understand the factors that affect the SOM persistence and vulnerability at the mineral interface.

Until now, researchers had only limited, qualitative information about organic-minerals at this interface. Using DFS, however, they could make comparisons between specific functional groups and mineral types under varying environmental conditions. Their findings indicate that environmental factors, such as ionic strength and pH, produce the most drastic differences in binding energies.

Their approach to obtaining direct and quantitative treatment of the organic–mineral interface could fundamentally inform next-generation land-carbon models in which mineral-bound carbon is an important control on carbon persistence. In turn, such models would be at the cutting edge of our current understanding of the terrestrial carbon cycle.

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

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

Funding
This research was supported by the Chemical Imaging Initiative through the LDRD Program at Pacific Northwest National Laboratory (PNNL). V.L.B. was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research as part of the Terrestrial Ecosystem Sciences Program.

Publications
Newcomb, C.J., et al. “Developing a molecular picture of soil organic matter–mineral interactions by quantifying organo–mineral binding.” Nature Communications, 8:396 (2017). [DOI:10.1038/s41467-017-00407-9]. (Reference link)

Topic Areas:

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



Schematic of the experimental setup. Common chemical functional groups from soil organic matter (SOM) were chosen to represent a model for interaction between organics and two model minerals: muscovite and goethite. Performing force measurements between these model organics and minerals enable us to quantitatively evaluate the binding energies. Source: Newcomb, C.J., et al. Figure reprinted under license to Creative Commons Attribution 4.0 International License.



August 29, 2017

An Effective-Medium-Based Model for P-Wave Velocities of Saturated, Unconsolidated Saline Permafrost

A new rock physics model provides superb fits to experiment data and important insights on pore-scale distributions of ice in saline permafrost.

The Science
The NGEE-Arctic team developed an effective-medium-based rock physics model for inferring ice content of saline permafrost from seismic P-wave velocities. Unlike many existing models that either only consider a single type of pore-scale ice distribution or rely on many tuning parameters to accounting for multiple ice distributions, our model only requires one free parameter to achieve superb data fits.

The Impact
The model provides important insights on pore-scale distributions of ice in saturated, unconsolidated saline permafrost. The modeling workflow is not only useful for permafrost, but also applicable to hydrate-bearing sediments. Their approach could also be generalizable to modeling cementation processes where both pore filling and contact cementing materials coexist in the pore space.

Summary
To better understand the relationship between P-wave velocities and ice content in saturated, unconsolidated saline permafrost, we constructed an effective-medium model based upon ultrasonic P-wave data that were obtained from earlier laboratory studies. The model uses a two-end-member mixing approach in which an ice-filled, fully frozen end member and a water-filled, fully unfrozen end member are mixed together to form the effective medium of partially frozen sediments. This mixing approach has two key advantages: (1) It does not require parameter tuning of the mixing ratios, and (2) it inherently assumes mixed pore-scale distributions of ice that consist of frame-strengthening (i.e., cementing and/or load-bearing) ice and pore-filling ice. The model-predicted P-wave velocities agree well with our laboratory data, demonstrating the effectiveness of the model for quantitatively inferring ice content from P-wave velocities. The modeling workflow is simple and is largely free of calibration parameters — attributes that ease its application in interpreting field data sets.

Contacts (BER PM)
Dan Stover
SC-23.1
Daniel.stover@science.doe.gov301-903-0289)

(PI Contact)
Jonathan Ajo-Franklin
Lawrence Berkeley National Laboratory
JBAjo-Franklin@lbl.gov

Funding
As part of the Next-Generation Ecosystem Experiments (NGEE-Arctic) project sponsored by the Office of Biological and Environmental Research in the DOE Office of Science, this study is supported through contract DEAC0205CH11231 to the Lawrence Berkeley National Laboratory and through contract DE-AC05-00OR22725 to the Oak Ridge National Laboratory.

Publications
Dou, Shan, Seiji Nakagawa, Douglas Dreger, and Jonathan Ajo-Franklin. ”An effective-medium model for P-wave velocities of saturated, unconsolidated saline permafrost.” Geophysics 82(3) P. EN33-EN50 (2017). [DOI:10.1190/geo2016-0474.1]

Topic Areas:


August 18, 2017

Lateral Processes Dominate Control of Water Available to Tropical Forests

Comparing models of different complexities provides important insights for improving drought response simulations.

The Science
The Amazon basin has experienced periodic droughts in the past, and intense, more frequent droughts are predicted. Comparing hydrologic models of different complexities and parameters in a catchment in central Amazonia, a research team led by scientists at the U.S. Department of Energy’s (DOE) Pacific Northwest National Laboratory found that variations in terrain have a dominant influence on groundwater table and streamflow through lateral transport of soil water. Hence, different models produce significantly different water available to plants. Despite the difference, however, plants were not under water stress in any simulation, even during a drought year. The team identified another important process—the efficiency of water transport through the plants—which must be better represented in models to more realistically simulate drought response.

The Impact
Tropical forests are an important carbon sink, but a large fraction of the carbon sequestered during normal and wet years can be released during drought years because of tree mortality and reduced ecosystem productivity. This research shed light on key processes that influence water available for plant use, and provided insights for improving modeling of tropical forest drought response.

Summary
To better understand how tropical forests respond to drought requires improved capabilities to predict the spatial variability of water and soil moisture available for plant use. Researchers in the United States and Brazil identified spatial variabilities in soil and topography as the dominant influences on soil hydrology in an Amazonian catchment. Scientists performed a series of numerical experiments using the one-dimensional DOE Accelerated Climate Modeling for Energy (ACME) Land Model (ALM) and the three-dimensional ParFlow hydrology model. Researchers found large differences in groundwater table depth between the models. By varying the model soil parameters, the team found that ALM can reproduce the long-term mean groundwater table depth simulated by ParFlow, but it cannot capture features such as delayed groundwater recharge at the plateau. This study showed that developing approaches to represent lateral processes that are missing in one-dimensional models is critical for modeling water available to plants in tropical forests. In addition, plant hydraulics (the efficiency of water transport through plants) and preferential flow (water movement through macropore soils) are key processes that should be represented in Earth system models for simulating tropical forest response to drought and the future of the land carbon sink. The results could apply to other catchments in the Amazon basin with similar seasonal variability and hydrologic regimes.

Contacts (BER PMs)
Daniel Stover
Terrestrial Ecosystem Science
Daniel.Stover@science.doe.gov

Dorothy Koch
Earth System Modeling
Dorothy.Koch@science.doe.gov

PI Contact
L. Ruby Leung
Pacific Northwest National Laboratory
Ruby.Leung@pnnl.gov

Funding
The U.S. Department of Energy Office of Science, Biological and Environmental Research supported this research as part of the Terrestrial Ecosystem Science program through the Next Generation Ecosystem Experiment (NGEE)-Tropics project.

Publication
Y. Fang, L.R. Leung, Z. Duan, M.S. Wigmosta, R.M. Maxwell, J.Q. Chambers, and J. Tomasella. “Influence of Landscape Heterogeneity on Water Available to Tropical Forests in an Amazonian Catchment and Implications for Modeling Drought Response.” Journal of Geophysical Research: Atmospheres, (2017). [DOI: 10.1002/2017JD027066]

Related Links
Reference link

Topic Areas:


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 18, 2017

Drought-induced mortality patterns and rapid biomass recovery in a terra firme forest in the Colombian Amazon

Investigation of the effects of a severe ENSO-related drought on biomass dynamics in a lowland rainforest in the Amazon.

The Science  
Tree mortality controls the forest carbon cycle. Extreme climatic events in the Amazon are expected to become more frequent, resulting in increased forest mortality. However, the extent to which individual drought events affect biomass loss, and the resulting resilience of Amazonian forests to drought, are not well understood. These baseline observations are critical for testing models of drought effects on forest carbon fluxes at a pantropical scale.

The Impact
In this study, researchers from the NGEE-Tropics research team tracked biomass dynamics in over 14,000 trees in 25-hectares of forest in the Colombian Amazon before and after an intense ENSO-related drought. Drought led to a significant reduction in forest biomass, with valley forests being more negatively affected than ridge forests. Surprisingly, however, the forest bounced back rapidly following the drought. Rapid biomass recovery suggests that these forests may be more resilient to periodic ENSO events than anticipated. 

Summary
Since understanding drivers of tree mortality is essential for modeling forest biomass responses to changing climatic and environmental conditions, this work makes an important contribution to the NGEE-Tropics project. The results suggest a high degree of resilience of this Amazonian forest to drought. Enhanced performance of drought-tolerant species that inhabit the drier ridges enabled forest resilience. The diversity of species' ecologies and physiologies may provide an important buffer for tropical forests during extreme climatic events. The results have important implications for understanding drought impacts elsewhere in the Amazon and in other tropical forest areas.

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

Dorothy Koch
SC-23.1
Dorothy.koch@science.doe.gov

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

Funding
Funds for the tree censuses were in part provided by the Smithsonian Institution Center for Tropical
Forest Science—Forest Global Earth Observatory (CTFS-ForestGEO). Additional funds came from the COLCIENCIAS funding program in Colombia for both plot census costs and a fellowship to DZ. SJD received support from the Next Generation Ecosystem Experiment (NGEE) Tropics project sponsored by the U.S. Department of Energy, Office of Biological and Environmental Research in the Office of Science.

Publications
Zuleta, D., A. Duque, D. Cardenas, H. C. Muller-Landau, and S. J. Davies. “Drought-induced mortality patterns and rapid biomass recovery in a terra firme forest in the Colombian Amazon” Ecology 98(10), 2538-2546 (2017). [DOI: 10.1002/ecy.1950]

Topic Areas:


July 10, 2017

Modeling Across Multiple Scales to Enable System-Level Understanding of a Watershed

Novel model structures allow advanced models of permafrost thermal hydrology to run at scale.

The Science
Field and laboratory observations and the models that are used to help understand the observed processes typically focus on relatively small scales, but the consequences of those processes must be evaluated at larger watershed or regional scales.  An intermediate-scale modeling approach has been developed to bridge this gap in scales and improve confidence in simulations of Arctic hydrology and permafrost dynamics.

The Impact
Broadly applicable to hydrology modeling, the approach makes it possible to include more detail in process representations, thus providing direct links between detailed field investigations and larger-scale models. The resulting model improves the representation of permafrost dynamics, which directly affect cold-region hydrology, Arctic infrastructure stability, and biogeochemical cycles.

Summary
Motivated by results from fine-scale simulations, scientists from Oak Ridge National Laboratory and Los Alamos National Laboratory developed an intermediate-scale model. The new model replaces a fully three-dimensional system with a two-dimensional overland thermal hydrology system and a family of one-dimensional vertical columns, where each column represents a thermal hydrology system coupling the surface and subsurface but without lateral flow. This approach accurately approximates the fully-resolved solution, but can be solved at significantly less computational cost. The computational advantages will enable state-of-the-art models of permafrost dynamics to be applied across large swaths of the Arctic.  Furthermore, the approach supports the broader strategy of using local models and field observations to reduce uncertainty in watershed, regional, and global Earth System Model predictions.

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

(PI Contact)
Ahmad Jan and Scott Painter
Climate Change Science Institute, Oak Ridge National Laboratory
jana@ornl.gov (865-576-8175) or paintersl@ornl.gov (865-241-2644)

Funding
This work was supported by Interoperable Design of Extreme-scale Application Software (IDEAS) project and by the Next Generation Ecosystem Experiment (NGEE-Arctic) project.

Publications
Jan, A., E. T. Coon, S. L. Painter, R. Garimella, and J. D Moulton, “An intermediate-scale model for thermal hydrology in low-relief permafrost-affected landscapes.” Comput Geosci 22, 163-177 (2017). [DOI:10.1007/s10596-017-9679-3]

Topic Areas:

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


July 05, 2017

Assessing a New Clue to How Much Carbon Plants Take Up

Tracking the carbonyl sulfide signal could open a new window into the carbon cycle.

The Science
Current climate models disagree on how much carbon dioxide land ecosystems take up for photosynthesis. In response, atmospheric scientists, biogeochemists, and oceanographers have proposed measuring a gas called carbonyl sulfide (COS) to help quantify the contribution that photosynthesis makes to carbon uptake.

The Impact
Photosynthesis is a key climate forcing process in the terrestrial biosphere. It removes CO2 from the atmosphere and stores carbon in plants, slowing the rate of climate change. Measurements of atmospheric COS provide the first global scale estimates of this carbon-climate feedback.

Summary
Ten years ago, scientists discovered a massive and persistent biosphere signal in atmospheric COS measurements. In these data, COS and CO2 levels follow a similar seasonal pattern, but the COS signal is much stronger over continental regions, suggesting that the terrestrial biosphere is a sink for COS. The remarkable discovery led scientists to wonder: Could COS be used as a tracer for carbon uptake?  An explosive growth in COS studies followed as scientists attempted to answer this question, including a COS record from the present to the Last Glacial Maximum, satellite-based maps of the dynamics of COS in the global atmosphere, and measurements of ecosystem fluxes of COS.

Contacts
(BER PM)

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

(PI Contact)
J. Elliott Campbell
UC Santa Cruz
elliott.campbell@ucsc.edu

Funding
DE-SC0011999

Publications
Campbell, J. Elliott, et al. 2017. "Assessing a New Clue to How Much Carbon Plants Take Up." Eos, 98, 24-29. 10.1029/2017EO075313.

Related Links
http://www.cosanova.org/

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 26, 2017

Large Uncertainty in Permafrost Carbon Stocks Due to Hillslope Soil Deposits

The Science  
The gradual and ongoing transport of soil and soil organic carbon down hillslopes results in deposits at the base of hills. Limited sampling of these deposits leaves the quantity of carbon buried on hills poorly quantified. Our analysis suggests that accounting for carbon in these deposits could significantly alter present estimates of carbon stored in permafrost.

The Impact
Quantifying the amount of carbon frozen and stored in permafrost soils is a critical challenge in the attempt to estimate the possible feedback thawing permafrost may have on the global carbon cycle. Given the widespread distribution and potential for deposits thicker that one meter, hillslope deposits of soil carbon could be a significant, but presently unaccounted-for store of carbon in permafrost regions. Greater study should be focused on these depositions to better constrain estimates of permafrost soil organic carbon stores.

Summary
We combined topographic models with soil profile data and topographic analysis to evaluate the quantity and uncertainty of soil organic carbon (SOC) mass stored in perennially frozen hill toe soil deposits. We show that in Alaska this SOC mass introduces an uncertainty that is >200% of the current state-wide estimates of SOC stocks (77 Pg C) and that a similarly large uncertainty may also pertain at a circumpolar scale. The SOC content of permafrost hill toe deposits can meaningfully change current estimates of permafrost SOC. SOC stored in hill toe deposits is likely sensitive to climate change-induced erosion and deposition. Soil sampling and geophysical imaging efforts that target hill toe deposits can help constrain this large uncertainty.

Contacts
(BER PM)

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

(PI Contact)
Joel C. Rowland
Los Alamos National Laboratory, Los Alamos, NM
jrowland@lanl.gov (505-665-2871)

Funding
This research is supported by the DOE Office of Science, Office of Biological and Environmental Research, Next Generation Ecosystem Experiment, NGEE-Arctic project. Contributions of U. Mishra were supported under Argonne National Laboratory contract DE-AC02-06CH11357.

Publications
Shelef, E., J. C. Rowland, C. J. Wilson, G. E. Hilley, U. Mishra, G. L. Altmann, and C.-L. Ping. 2017. “Large Uncertainty in Permafrost Carbon Stocks Due to Hillslope Soil Deposits”, Geophys. Res. Lett., DOI:10.1002/2017GL073823.

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 20, 2017

Tree Hydraulic Acclimation Partially Mitigates Effects of Warming and Drought

Tree water dynamics under warming and drying conditions.

The Science 
A novel tree manipulation study shows the roles of hydraulic acclimation to both precipitation and temperature in two tree species and unravels their effects.

The Impact
Analysis of a vast number of tree-water dynamics observations shows juniper and piñon trees have different physiological responses to heat and drought stress including varying ability to acclimate.  Our new framework allows separation of temperature and precipitation responses in these species, and provides a path forward for better model representations of how trees will function within the evolving Earth system.

Summary
Previous findings suggested warming superimposed on drought would exacerbate drought stress and increase mortality. However, during this study’s five-year period of warmer and much drier conditions, no mortality was observed. The tree stomata adjusted to heat and drought even when other functions were drastically impaired by drought—stomata acclimation prevented tree death from the additive effects of warming and drying. Also, previous work had revealed that juniper trees can be highly resistant to drought, keeping their stomata open, while piñon shut down all functions that kept them alive. However, in this study, juniper was unable to significantly acclimate and showed strong reductions in function. Piñon, which suffered when exposed to drought, acclimated when warming was the only stressor. Piñon retained hydrological functions including sap production to repel invaders.

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)

Renu Joseph SC-23.1
renu.joseph@science.doe.gov (301-903-9237)

(PI Contact)
Charlotte Grossiord
MS J495
Los Alamos National Laboratory
Los Alamos, NM, 87545
505 665 2450

Funding
The Los Alamos Survival-Mortality (SUMO) Experiment was funded by the US Department of Energy, Office of Science, Biological and Environmental Research.

Publications
Grossiord, et al. 2017. “Tree water dynamics in a drying and warming world,” Plant, Cell & Environment 40, 1861-1873. DOI: 10.1111/pce.12991.

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


June 07, 2017

Inter-Annual Variability of Net and Gross Ecosystem Carbon Fluxes

A review.

The Science
Interannual variability in net carbon exchange in terrestrial ecosystems is large relative to its long-term mean. Furthermore, ecosystem photosynthesis contributed more to net carbon exchange than respiration.

The Impact
Long-term carbon flux measurements are needed for many reasons. Most importantly, these measurements enable the study of ecosystems on ecosystem time scales, which exceed decades. Long-term flux studies are needed to provide information on whether or not, and if so, how fast, ecosystem metabolism may be responding to a changing world that is warmer, bathed in more CO2, experiencing variation in rainfall and different degrees of nitrogen deposition, air pollution and disturbance from humans, diseases, and pests. This behavior, co-occurring with other Earth system changes such as increasing global temperatures, a changing hydrological cycle and rising atmospheric CO2 levels, will contribute to critically important longer time series measurements.

Summary
As the lifetime of regional flux networks approach twenty years, there are a growing number of papers that have published long-term records (5 years or more) of net carbon fluxes between ecosystems and the atmosphere. Unanswered questions from this body of work are: 1) how variable are carbon fluxes on a year to year basis? 2) what are the biophysical factors that may cause interannual variability and/or temporal trends in carbon fluxes? and 3) how does the biophysical control on this carbon flux variability differ by climate and ecological spaces? To address these questions, researchers surveyed published data from 59 field study sites that reported on five or more years of continuous measurements, yielding 544 site-years of data.

A disproportionate fraction of the yearly variability in net ecosystem exchange was associated with biophysical factors that modulated ecosystem photosynthesis rather than ecosystem respiration. Yet, there was appreciable and statistically significant covariance between ecosystem photosynthesis and respiration. Consequently, biophysical conditions that conspired to increase ecosystem photosynthesis from one year to the next were associated with an increase in ecosystem respiration, and vice versa; on average, the year-to-year change in respiration was 40% as large as the year to year change in photosynthesis. The analysis also identified sets of ecosystems that are on the verge of switching from being carbon sinks to carbon sources. These include sites in the Arctic tundra, the evergreen forests in the Pacific Northwest and some grasslands, where year-to-year changes in respiration are outpacing those in photosynthesis.

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

(PI Contact)
Dennis Baldocchi
University of California, Berkeley
baldocchi@berkeley.edu

Funding
This research was supported by funding from the U.S. Department of Energy, Terrestrial Ecosystem Science program, and its support of the FLUXNET and AmeriFlux projects. 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 FLUXNET was under contract DESC0012456

Publications
Baldocchi, Dennis, Housen Chu, and Markus Reichstein. “Inter-annual variability of net and gross ecosystem carbon fluxes: A review.” Agricultural and Forest Meteorology, 249: 520-533 (2018). [DOI: 10.1016/j.agrformet.2017.05.015]

Related Links
(Reference link)

Topic Areas:


June 03, 2017

Coincident Aboveground and Belowground Autonomous Monitoring to Quantify Covariability in Permafrost, Soil, and Vegetation Properties in Arctic Tundra

Quantification of codynamics between permafrost, soil and vegetation properties.

The Science
A novel monitoring strategy was developed to quantify complex Arctic ecosystem responses to the seasonal freeze-thaw-growing season conditions. The spatially and temporally dense monitoring data sets revealed several insights about tundra system behavior at a site located near Barrow, Alaska.

The Impact
Coincident monitoring of the spatiotemporal distribution of and interactions between land, soil, and permafrost properties is important for advancing our predictive understanding of ecosystem dynamics. Demonstration of this first aboveground and belowground geophysical monitoring approach within an Arctic ecosystem illustrates its significant potential to remotely “visualize” permafrost, soil, and vegetation ecosystem codynamics in high resolution over field relevant scales.

Summary
The novel strategy exploited autonomous measurements obtained through electrical resistivity tomography to monitor soil properties, pole-mounted optical cameras to monitor vegetation dynamics, point probes to measure soil temperature, and periodic measurements of thaw layer thickness, snow thickness, and soil dielectric permittivity. Among other results, the soil electrical conductivity (a proxy for soil water content) in the active layer indicated an increasing positive correlation with the green chromatic coordinate (a proxy for vegetation vigor) over the growing season, with the strongest correlation (R = 0.89) near the typical peak of the growing season. Soil conductivity and green chromatic coordinate also showed significant positive correlations with thaw depth, which is influenced by soil and surface properties. These correlations have been then confirmed at larger spatial scale using an unmanned aerial system (UAS) platform.

Contacts
(BER PM)

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

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

LBNL POC:
Susan Hubbard
Lawrence Berkeley National Laboratory
sshubbard@lbl.gov

Funding
The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science. This NGEE-Arctic research is supported through contract number DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory.

Publications
Dafflon, B., R. Oktem,  J. Peterson,  C. Ulrich, A.P. Tran, V. Romanovsky, and S.S. Hubbard. 2017. “Coincident Aboveground and Belowground Autonomous Monitoring to Quantify Covariability in Permafrost, Soil, and Vegetation Properties in Arctic Tundra,” Journal of Geophysical Research: Biogeosciences, 122(6), 1321-1342. DOI: 10.1002/2016JG003724.

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 12, 2017

Quantification of Arctic Soil and Permafrost Properties Using Ground Penetrating Radar and Electrical Resistivity Tomography Datasets

Improved quantification of Arctic soil and permafrost properties.

The Science
We developed an approach to improve the estimation of ice-wedge dimension and other permafrost characteristics by integrating various geophysical imaging techniques including Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT).

The Impact
Improving understanding of Arctic ecosystem climate feedback and parameterization of models that simulate freeze-thaw dynamics require advances in quantifying soil and snow properties This work enables a better understanding and quantification of the morphology and physical properties of ice-wedges and permafrost present in Arctic tundra.

Summary
We document for the first time that GPR data collected during the frozen season, when conditions lead to improved GPR signal-to-noise ratio, can provide reliable estimates of active layer thickness and geometry of ice wedges. We find that the ice-wedge geometry extracted from GPR data collected during the frozen season is consistent with ERT data, and that GPR data can be used to constrain the ERT inversion. Consistent with recent studies, we also find that GPR data collected during the frozen season can provide good estimates of snow thickness, and that GPR data collected during the growing season can provide reliable estimate thaw depth. Our quantification of the value of the GPR and ERT data collected during growing and frozen seasons paves the way for coupled inversion of the datasets to improve understanding of permafrost variability.

Contacts
(BER PM)

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

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

LBNL POC:
Susan Hubbard
Lawrence Berkeley National Laboratory
sshubbard@lbl.gov

Funding
The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science. This NGEE-Arctic research is supported through contract number DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory.

Publications
Léger, E., B. Dafflon, F. Soom, J. Peterson, C. Ulrich, and S. Hubbard. 2017. “Quantification of Arctic Soil and Permafrost Properties Using Ground-Penetrating Radar and Electrical Resistivity Tomography Datasets,” IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 99, 1-12. DOI: 10.1109/JSTARS.2017.2694447

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


May 04, 2017

How Plant Roots Take Up Water from Soil

A combined experimental and modeling approach quantitatively demonstrates in 3D the transport of water from the surrounding rhizosphere through plant roots.

The Science
Root water uptake is one of the most important processes in subsurface flow and transport modeling. It is driven by transpiration caused by the water potential gradient between the atmosphere and the plant. But the mechanisms of root water uptake are poorly known, and are represented only coarsely in macro-scale models because of the difficulties of both imaging and modeling such systems.

A new paper in the journal Rhizosphere, by Timothy D. Scheibe and three co-authors at the Pacific Northwest National Laboratory (PNNL), demonstrates a promising way to address those difficulties. In a pilot study, they successfully simulate three-dimensional root water uptake by applying a combination of X-ray Computed Tomography (XCT) and computational fluid dynamics (CFD) modeling at the pore-scale.

The Impact
The new coupled imaging-modeling approach introduces a realistic platform for investigating rhizosphere flow processes - one that could support translation of process understanding from a single-plant to vegetation scales. The same imaging-modeling method could also be used to simulate more realistic scenarios and compared to laboratory and field plot studies to improve process understanding.

Summary
Successful in-soil imaging of a live plant could unlock mysteries regarding the complex plant-soil-microbe interactions in the rhizosphere. This plant-root interface, teeming with microorganisms and bathed in water at every scale, is where complex chemical, biological, and physical interactions determine the health of plants, their root systems, and the surrounding soil.

To date, however, imaging and modeling root water uptake has been difficult. The complexity of the root architecture and soil properties makes explicit imaging problematic. Estimating plant-root and soil properties for modeling is also difficult, compounded by a poor understanding of the hydrological and biological processes involved in root water uptake.

In the last decade, a promising series of papers has shown the potential of integrating high-resolution imaging techniques and pore-scale modeling for investigating the interactions of soil, roots, and groundwater.

A team at PNNL recently combined non-invasive XCT imaging with both open-source and in-house software codes. They successfully imaged root water uptake at a micron-scale resolution in 3D and they also modeled the spatiotemporal variations of water uptake. What they call a “pioneer” pilot study provides a platform for future research into the role of plant roots in nutrient uptake, hydraulic redistribution, and other phenomena in the rhizosphere.

The researchers used a single Prairie dropseed (Sporobolus heterolepis) plant grown in a pot, which was rotated continuously during a scan that captured 3,142 projections (at four frames per projection). The raw images were used to create a three-dimensional dataset. From there, in-house PNNL software derived quantitative information, including root volume and surface area. The result was a mechanistic pore-scale numerical model of root uptake processes.

The study showed that soil water distribution was controlled by both plant-root and soil conductivity, and by transpiration rate. But more broadly, it demonstrated a realistic platform for investigating rhizosphere flow processes.

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

Paul Bayer, Subsurface Biogeochemical Research
Paul.Bayer@science.doe.gov
(301) 903-5324

Dan Stover, Terrestrial Ecosystem Sciences
Dan.Stover@science.doe.gov
(301) 903-0289

PI Contact
Timothy D. Scheibe
Pacific Northwest National Laboratory
Tim.scheibe@pnnl.gov (509-371-7633)

Funding
This research was supported by the U.S. Department of Energy (DOE) Biological and Environmental Research (BER) Division through the Terrestrial Ecosystem Science (TES) program and the Subsurface Biogeochemical Research (SBR) program, through the PNNL SBR Scientific Focus Area Project. Part of this research was performed at the Environmental Molecular Sciences Laboratory (EMSL), a DOE scientific user facility located at Pacific Northwest National Laboratory (PNNL).

Publication
Yang, X., T. Varga, C. Liu, and T.D. Scheibe. “What can we learn from in-soil imaging of a live plant: X-ray Computed Tomography and 3D numerical simulation of root soil system.” Rhizosphere 3(2), 259-262 (2017). [DOI: 10.1016/j.rhisph.2017.04.017]
(Reference link)

Related Links
PubMed: “Extracting Metrics for Three-dimensional Root Systems: Volume and Surface Analysis from In-soil X-ray Computed Tomography Data” J Vis Exp. 2016 Apr 26;(110). [DOI:10.3791/53788]
Soil Science Society of America Journal Abstract - Soil Physics: “A Unified Multiscale Model for Pore-ScaleFlow Simulations in Soils” [DOI:10.2136/sssaj2013.05.0190]

Topic Areas:


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)]



February 03, 2017

Will Seasonally Dry Tropical Forests Be Sensitive or Resistant to Future Changes in Rainfall Regime?

A review of scientific literature on responses of seasonally dry tropical forests to changing rainfall.

The Science
Seasonally dry tropical forests experience periodic droughts that occur each year but it is unknown how their organisms and ecosystem processes will respond to increasing climatic variability including extreme droughts and/or changes in the timing, duration or magnitude of rainfall regimes. This uncertainty has led to two very different predictions: some people argue that seasonally dry tropical forests will be very sensitive to changes in rainfall because they are already at hydrologic thresholds, while others claim that they will be resistant because these species are already adapted to strong seasonal drought. This paper reviewed existing studies with the goals of searching for general patterns that could discriminate between these two hypotheses and also to identify gaps in the literature to guide future research.

The Impact
This review found that there are many potential ways for "drought" to be manifested in seasonally dry tropical forests. Importantly, most of the studies are consistent with the prediction that changing rainfall regimes will have large effect on species composition and ecological function of these forests.

Summary
By the end of the 21st century, climate models predict substantial changes in rainfall regimes across the seasonally dry tropical forest biome, but little is known about how dry forests will cope with the hotter, drier conditions predicted by climate models. We explored two alternative hypotheses: 1) dry forests will be sensitive to drought because they are already limited by water and close to hydrologic thresholds, or 2) they will be resistant/resilient to intra- and inter-annual changes in rainfall because they are adapted to predictable, seasonal drought. In our review of literature spanning microbial to ecosystem scales, most studies suggests that increasing frequency and intensity of droughts in dry forests will likely alter species distributions and ecosystem processes. Though we conclude that dry forests will be sensitive to altered rainfall regimes, many gaps in the literature remain. Future research should focus on geographically comparative studies and well-replicated drought experiments that can provide empirical evidence to improve simulation models used to forecast dry forest responses to future climate change at coarser spatial and temporal scales.

Contacts (BER PM)
Jennifer Powers
University of Minnesota, Departments of Ecology, Evolution, and Behavior and Plant and Microbial Biology
powers@umn.edu

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

Funding
We thank the US Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science (TES) Program under award number DE-SC0014363 for funding. JSP also thanks the US National Science Foundation CAREER Award DEB-1053237.

Publications
Allen, K. et al. “Will seasonally dry tropical forests be sensitive or resistant to future changes in rainfall regimes?,” Environmental Research Letters 12, 023001 (2017). doi:10.1088/1748-9326/aa5968.

Topic Areas:

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


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

Evapotranspiration Across Plant Types and Geomorphological Units in Polygonal Arctic Tundra

Plant types and geomorphological location affect evapotranspiration

The Science 
A group of scientists conducted a field research campaign over two summers at an Arctic tundra site near Barrow, Alaska, to measure water vapor fluxes (evapotranspiration) from different characteristic plant types, bare soil and open water, to understand the variations and the controls over these fluxes across the landscape.

The Impact
The research showed that evapotranspiration from mosses and open water was twice as high as that from lichens and bare ground, and that microtopographic variations in polygonal tundra explained most of this and other spatial variation in evapotranspiration.

Summary
Coastal tundra ecosystems are relatively flat, yet display large spatial variability in ecosystem traits. The microtopographical differences in polygonal geomorphology produce heterogeneity in permafrost depth, soil temperature, soil moisture, soil geochemistry, and plant distribution. Few measurements have been made, however, of how water fluxes vary across polygonal tundra plant types, limiting our ability to understand and model these ecosystems. In this study, we investigated how plant distribution and geomorphological location affect actual evapotranspiration (ET). These effects are especially critical in light of the rapid change polygonal tundra systems are experiencing with Arctic warming. At a field site near Barrow, Alaska, USA, we investigated the relationships between ET and plant cover in 2014 and 2015. ET was measured at a range of spatial and temporal scales using: (1) An eddy covariance flux tower for continuous landscape-scale monitoring; (2) An automated clear surface chamber over dry vegetation in a fixed location for continuous plot-scale monitoring; and (3) Manual measurements with a clear portable chamber in approximately 60 locations across the landscape. We found that variation in environmental conditions and plant community composition, driven by microtopographical features, has significant influence on ET. Among plant types, ET from moss-covered and inundated areas was more than twice that from other plant types. ET from troughs and low polygonal centers was significantly higher than from high polygonal centers. ET varied seasonally, with peak fluxes of 0.14 mm h-1 in July. Despite 24 hours of daylight in summer, diurnal fluctuations in incoming solar radiation and plant processes produced a diurnal cycle in ET. Combining the patterns we observed with projections for the impact of permafrost degradation on polygonal structure, the suggestion is that microtopographic changes associated with permafrost thaw have the potential to alter tundra ecosystem ET.

Contacts
(BER PM)

Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov

(PI Contact)
Author: Naama Raz-Yaseef
Lawrence Berkeley National Laboratory
nryaseef@lbl.gov

LBNL POC: Susan Hubbard
Lawrence Berkeley National Laboratory
sshubbard@lbl.gov  

PI: Stan Wullschleger
Oak Ridge National Laboratory
wullschlegsd@ornl.gov

Funding
The Next-Generation Ecosystem Experiments (NGEE Arctic) project is supported by the Office of Biological and Environmental Research in the DOE Office of Science.

Publications
Raz-Yaseef, N., J. Young-Robertson, T. Rahn, V. Sloan, B. Newman, C. Wilson, S.D. Wullschleger, M.S. Torn. 2017. “Evapotranspiration Across Plant Types and Geomorphological Units in Polygonal Arctic Tundra,” Journal of Hydrology 553, 816-825. DOI: 10.1016/j.jhydrol.2017.08.036.

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