BER Research Highlights

Search Date: December 13, 2017

53 Records match the search term(s):


December 15, 2016

Seedling Responses to Climate Warming May Slow Tree Advance Upslope

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

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

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

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

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

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

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

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

Related Link
Alpine-Treeline Warming Experiment website

Topic Areas:

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



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



December 08, 2016

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

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

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

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

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

Contacts
(BER PM)

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

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

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

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

Topic Areas:

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


November 28, 2016

Roadmap for Improving the Representation of Photosynthesis in Earth System Models

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

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

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

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

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

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

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

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

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

Topic Areas:

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


November 24, 2016

A Trait-Based Plant Hydraulics Model For Tropical Forests

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

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

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

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

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

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

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

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

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

Topic Areas:

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


November 21, 2016

Tropical Tree Photosynthesis and Nutrients: the Model-Data Connection

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

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

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

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

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

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

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

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

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

Topic Areas:

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


November 16, 2016

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

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

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

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

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

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

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

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

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

Topic Areas:

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


November 16, 2016

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

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

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

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

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

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

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

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

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

Topic Areas:

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


November 15, 2016

How Moisture Affects the Way Soil Microbes Breathe

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

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

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

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

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

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

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

Contacts
(BER PM)

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

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

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

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

Topic Areas:

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



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



November 15, 2016

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

4 April 2017

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

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

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

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

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

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

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

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

Topic Areas:

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


November 15, 2016

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

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

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

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

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

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

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

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

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

Topic Areas:

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


November 14, 2016

Temperature Response of Soil Respiration Largely Unaltered with Experimental Warming

Global temperature response of soil respiration is consistent across biomes.

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

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

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

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

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

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

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

Topic Areas:

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


November 11, 2016

Biogenic Volatile Organic Compounds in Amazonian Ecosystems

Biochemical fingerprints provide clues on tropical forest processes

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

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

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

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

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

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

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

Topic Areas:

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


November 10, 2016

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

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

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

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

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

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

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

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

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

Topic Areas:

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


October 14, 2016

Dynamic Vertical Profiles of Peat Porewater Chemistry in a Northern Peatland

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

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

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

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

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

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

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

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

Related Links
SPRUCE

Topic Areas:

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


October 12, 2016

Unraveling the Molecular Complexity of Cellular Machines and Environmental Processes

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

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

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

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

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

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

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

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

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

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

Topic Areas:

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



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



October 11, 2016

Partitioning Controls on Tropical Evergreen Forest Photosynthesis across Timescales

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

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

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

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

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

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

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

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

Topic Areas:

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


September 29, 2016

Soil Moisture Data: When Is There Enough?

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

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

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

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

Contacts
(BER PM)

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

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

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

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

Topic Areas:

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


September 23, 2016

Soil Will Absorb Less Atmospheric Carbon Than Expected This Century

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

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

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

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

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

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

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

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

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

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

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

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

Topic Areas:

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



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



September 21, 2016

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

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

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

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

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

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

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

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

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

Topic Areas:

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


September 19, 2016

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

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

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

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

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

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

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

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

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

Topic Areas:

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


September 14, 2016

Aquatic Plants Accelerate Arctic Methane Emissions

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

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

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

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

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

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

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

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

Related Links
EOS article

Topic Areas:

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


September 13, 2016

A Belowground Perspective On Forest Drought

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

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

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

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

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

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

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

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

Topic Areas:

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


September 13, 2016

Improving Global Methane Emission Predictions

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

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

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

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

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

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

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

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

Topic Areas:

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


September 12, 2016

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

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

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

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

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

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

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

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

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

Topic Areas:

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


September 01, 2016

Alaska Arctic Vegetation Archive

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

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

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

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

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

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

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

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

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

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

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

Topic Areas:

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


August 27, 2016

Global Model Improved by Incorporating New Hypothesis for Vegetation Nutrient Limitation

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

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

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

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

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

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

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

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

Topic Areas:

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


August 22, 2016

The Energetic and Carbon Economic Origins of Leaf Thermoregulation

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

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

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

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

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

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

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

Topic Areas:

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


August 20, 2016

Characterizing Peatland Uptake and Losses of Carbon

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

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

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

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

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

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

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

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

Related Link
SPRUCE

Topic Areas:

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


August 13, 2016

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

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

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

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

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

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

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

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

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

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

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

Related Links
LEF Tower Data

Topic Areas:

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


August 11, 2016

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

New multiphysics simulation capability improves permafrost thermal hydrology projections.

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

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

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

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

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

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

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

Topic Areas:

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


July 29, 2016

Assessing Challenges and Benefits of an Online “Open Experiment”

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

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

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

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

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

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

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

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

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

Topic Areas:

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


July 16, 2016

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

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

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

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

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

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

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

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

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

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

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

Topic Areas:

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


July 14, 2016

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

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

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

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

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

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

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

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

Topic Areas:

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


July 06, 2016

Enabling Remote Prediction of Leaf Age in Tropical Forest Canopies

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

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

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

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

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

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

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

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

Topic Areas:

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



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



June 27, 2016

Climate Study Finds Human Fingerprint in Northern Hemisphere

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

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

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

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

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

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

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

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

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

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

Topic Areas:

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



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



June 27, 2016

Improving Predictions of Heterotrophic Respiration

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

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

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

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

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

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

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

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

Topic Areas:

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


June 13, 2016

Thawing Permafrost Could Accelerate Carbon Releases to the Atmosphere

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

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

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

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

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

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

Funding
Financial support was provided by the National Science Foundation (NSF) Vulnerability of Permafrost Carbon Research Coordination Network grant 955713, with continued support from the NSF Research Synthesis and Knowledge Transfer in a Changing Arctic: Science Support for the Study of Environmental Arctic Change grant 1331083. Additional funding came from the Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program (DE-SC0006982); United Kingdom Natural Environment Research Council (NE/K000179/1); German Research Foundation (Excellence cluster CliSAP); Department of Ecosystem Biology, Grant agency of South Bohemian University, GAJU project numbers 146/2013/P and 146/2013/D; NSF Office of Polar Programs (1312402); NSF Division of Environmental Biology (0423385 and 1026843); European Union (FP-7-ENV-2011, project PAGE21, contract number 282700); Academy of Finland (project CryoN, decision number 132 045); Academy of Finland (project COUP, decision number 291691; part of the European Union Joint Programming Initiative, Climate); University of Eastern Finland (project FiWER); Maj and Tor Nessling Foundation; and Nordic Center of Excellence (project DeFROST).

Publication
Schädel, C., M. K. F. Bader, E. A. G. Schuur, C. Biasi, R. Bracho, P. Capek, S. De Baets, K. Diakova, J. Ernakovich, C. Estop-Aragones, D. E. Graham, I. P. Hartley, C. M. Iversen, E. Kane, C. Knoblauch, M. Lupascu, P. J. Martikainen, S. M. Natali, R. J. Norby, J. A. O'Donnell, T. R. Chowdhury, H. Santruckova, G. Shaver, V. L. Sloan, C. C. Treat, M. R. Turetsky, M. P. Waldrop, and K. P. Wickland. 2016. “Potential Carbon Emissions Dominated by Carbon Dioxide from Thawed Permafrost Soils,” Nature Climate Change, DOI: 10.1038/nclimate3054. (Reference link)

Related Links
NGEE Artic
Northern Arizona University news release
ORNL news release
University of Exeter news release
Michigan Tech news release

Topic Areas:

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



The coastal wetlands and polygonal landscapes on the North Slope of Alaska encompass a range of dry, aerobic tundra and wet, anaerobic tundra. [Image courtesy U.S. Department of Energy, Oak Ridge National Laboratory]



High-centered polygons in Barrow, Alaska, include dry, aerobic tundra surrounded by wet, anaerobic soils. [Image courtesy U.S. Department of Energy, Oak Ridge National Laboratory]



May 31, 2016

Microbial Protein Structure Altered when Exposed to Soil Mineral Surfaces

New findings may improve predictions using decomposition models and shed light on potential changes in protein activity.

The Science
The degradation of soil organic matter by microbes plays an important role in atmospheric carbon levels. A recent study examined how soil minerals could affect the stability of microbial proteins, potentially influencing the rate of carbon dioxide release into the atmosphere.

The Impact
The study shows that interactions with the surface of birnessite, but not other common soil minerals, have the potential to substantially alter the structure of bacterial proteins. These findings shed new light on how protein-mineral interactions could affect degradation rates of soil organic matter.

Summary
Soil contains the largest amount of terrestrial carbon on the planet, so a small change in soil carbon can have a large impact on atmospheric carbon dioxide levels. Therefore, understanding how organic carbon is released from soil into the atmosphere is a key question in climate science. Microbes produce enzymes that interact with soil minerals, and these protein-mineral interactions play an important role in the decomposition of soil organic carbon, which is subsequently released into the atmosphere. Not clear, however, is how different soil minerals affect the structure and function of microbial enzymes. To address this question, a team of researchers from the Department of Energy’s (DOE) Environmental Molecular Sciences Laboratory (EMSL), Oregon State University, and Leibniz Zentrum für Agrarlandschaftsforschung conducted molecular dynamics simulations to determine how interactions with surfaces of five common soil minerals affect the structure of a small bacterial protein called Gb1. The team performed simulations using the Cascade high-performance computer at EMSL, a DOE Office of Science user facility. The researchers found the Gb1 structure becomes highly altered due to interactions with Na+-birnessite mineral surfaces, but not kaolinite, montmorillonite, and goethite mineral surfaces. Interactions with birnessite caused the Gb1 protein structure to flatten and partially unravel. These findings shed light on how different soil minerals could affect the stability of microbial enzymes, thereby influencing the degradation rate of soil organic carbon. These insights build on previous, published experimental observations and could lead to more accurate projections of how much carbon dioxide could be released into the atmosphere as a result of microbial decomposition of soil organic matter.

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

PI Contact
Amity Andersen
Environmental Molecular Sciences Laboratory
Pacific Northwest National Laboratory
amity.andersen@pnnl.gov

Funding
This work was supported by the Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, including support of the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science user facility; and the “Understanding Molecular-Scale Complexity and Interactions of Soil Organic Matter” Intramural Project at EMSL.

Publication
Andersen, A., P. N. Reardon, S. S. Chacon, N. P. Qafoku, N. M. Washton, and M. Kleber. 2016. “Protein-Mineral Interactions: Molecular Dynamics Simulations Capture Importance of Variations in Mineral Surface Composition and Structure,” Langmuir 32(24), 6194-209. DOI: 10.1021/acs.langmuir.6b01198. (Reference link)

Related Links
EMSL article: Microbial Protein's Structure can be Altered when Exposed to Soil Mineral Surfaces
EMSL article: Abiotic Pathway Makes Organic Nitrogen Compounds Available to Microbes and Plants

Topic Areas:

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


May 19, 2016

Variation in Stem Mortality Rates Determines Patterns of Above-Ground Biomass in Amazonian Forests: Implications for Dynamic Global Vegetation Models

Stem Mortality Controls Tropical Forest Biomass.

The Science             
Provides several key benchmarks for vegetation models in the Amazon basin via 1) spatial pattern maps of mortality, woody net primary productivity (NPP) and above-ground biomass (AGB), and 2) the underlying mechanisms controlling these patterns.

The Impact
Previous work had supposed that spatial patterns in AGB in Amazon forests were mediated by a positive association between woody NPP and stem mortality rates inducing reductions in AGB.  In contrast, we found that woody NPP and stem mortality are not correlated, and instead that spatial variability in AGB is controlled primarily by stem mortality (not woody biomass loss).

Summary
Understanding the processes that determine above-ground biomass (AGB) in Amazonian forests is important for predicting the sensitivity of these ecosystems to environmental change and for designing and evaluating dynamic global vegetation models (DGVMs). AGB is determined by inputs from woody net primary productivity (NPP) and the rate at which carbon is lost through tree mortality. Here, we test whether two direct metrics of tree mortality (the absolute rate of woody biomass loss and the rate of stem mortality) and/or woody NPP, control variation in AGB among 167 plots in intact forest across Amazonia. The observations show that stem mortality rates, rather than absolute rates of woody biomass loss, are the most important predictor of AGB, which is consistent with the importance of stand size structure for determining spatial variation in AGB. The relationship between stem mortality rates and AGB varies among different regions of Amazonia, indicating that variation in wood density and height/diameter relationships also influences AGB. In contrast to previous findings, we find that woody NPP is not correlated with stem mortality rates and is weakly positively correlated with AGB. The spatial pattern maps of mortality, net primary productivity and above-ground biomass (AGB), as well as the underlying mechanisms controlling these patterns provide key benchmark targets for DGVMs in Amazonia.

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

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

Funding (DOE component in bold)
This paper is a product of the European Union's Seventh Framework Programme AMAZALERT project (282664). The field data used in this study have been generated by the RAINFOR network, which has been supported by a Gordon and Betty Moore Foundation grant, the European Union's Seventh Framework Programme projects 283080, ‘GEOCARBON'; and 282664, ‘AMAZALERT'; ERC grant ‘Tropical Forests in the Changing Earth System'), and Natural Environment Research Council (NERC) Urgency, Consortium and Standard Grants ‘AMAZONICA' (NE/F005806/1), ‘TROBIT' (NE/D005590/1) and ‘Niche Evolution of South American Trees' (NE/I028122/1). Additional data were included from the Tropical Ecology Assessment and Monitoring (TEAM) Network - a collaboration between Conservation International, the Missouri Botanical Garden, the Smithsonian Institution and the Wildlife Conservation Society, and partly funded by these institutions, the Gordon and Betty Moore Foundation, and other donors. Fieldwork was also partially supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico of Brazil (CNPq), project Programa de Pesquisas Ecológicas de Longa Duração (PELD-403725/2012-7). A.R. acknowledges funding from the Helmholtz Alliance ‘Remote Sensing and Earth System Dynamics'; L.P., M.P.C. E.A. and M.T. are partially funded by the EU FP7 project ‘ROBIN' (283093), with co-funding for E.A. from the Dutch Ministry of Economic Affairs (KB-14-003-030); B.C. was supported in part by the US DOE (BER) NGEE-Tropics project (subcontract to LANL). O.L.P. is supported by an ERC Advanced Grant and is a Royal Society-Wolfson Research Merit Award holder. P.M. acknowledges support from ARC grant FT110100457 and NERC grants NE/J011002/1, and T.R.B. acknowledges support from a Leverhulme Trust Research Fellowship.

Publications
Johnson, M. O. et al. Variation in stem mortality rates determines patterns of above-ground biomass in Amazonian forests: implications for dynamic global vegetation models. Global Change Biology 22, 3996-4013, 2016. DOI:10.1111/gcb.13315 . (Reference link)

Topic Areas:

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


May 18, 2016

Influences and Interactions of Inundation, Peat, and Snow on Active Layer Thickness

New study details active layer response across gradients of environmental conditions in Arctic permafrost.

The Science
Researchers used a physics-based numerical model validated at the Barrow (Alaska) Environmental Observatory to simulate the subsurface thermal hydrological response in permafrost tundra due to changing environmental conditions in organic soil layer thickness, snow depth, soil saturation, and ponded depth. 

The Impact
Researchers mapped the complex interaction of isolated environmental conditions that govern permafrost conditions. As a result, Arctic tundra response to changing conditions either by naturally occurring environmental gradients or by climate-induced perturbations can be inferred.

Summary
The collective work provides details on active layer thickness (ALT), or annual thaw depth above permafrost, related to three important environmental conditions characteristic of Arctic permafrost tundra: (1) organic soil layer thickness, (2) snow depth, and (3) unsaturated to inundated conditions. The work teases out how ALT will change as gradients along these environmental conditions are traversed in either space or time. One finding indicates that wetting or drying of polygonal tundra appears to have a minor effect on ALT compared to organic layer thickness and snow. At the same time, however, the inundation state is very interactive and can act to amplify other conditions that influence ALT; so much so, that subsurface thermal tipping points can be crossed. For example, the combined effect of inundation depth and snow can cause taliks, zone of year-round unfrozen soil, to form.

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

(PI Contact)
Adam Atchley
Los Alamos National Laboratory
aatchley@lanl.gov; 505-665-6803

Funding
This work was supported by Los Alamos National Laboratory, Laboratory Direction Research and Development project LDRD201200068DR; and the Next-Generation Ecosystem Experiments (NGEE-Arctic) project, which is supported by the Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program.  

Publications
Atchley, A. L., E. T. Coon, S. L. Painter, D. R. Harp, and C. J. Wilson. 2016. “Influences and Interactions of Inundation, Peat, and Snow on Active Layer Thickness,” Geophysical Research Letters 43(10), 5116-23. DOI: 10.1002/2016GL068550. (Reference link)

Atchley, A. L., S. L. Painter, D. R. Harp, E. T. Coon, C. J. Wilson, A. K. Liljedahl, and V. E. Romanovskey. 2015. “Using Field Observations to Inform Thermal Hydrology Models of Permafrost Dynamics with ATS (v0.83),” Geoscientific Model Development 8, 2701-22. DOI: 10.5194/gmd-8-2701-2015. (Reference link)

Topic Areas:

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


May 11, 2016

Shrubs Accelerate Wetland Water Loss

As shrubs encroach, their leaves drive the “wet” out of wetlands.

The Science
Water is a defining characteristic of wetlands and a key influence on biodiversity and biogeochemistry. Unfortunately, climate change and water management are making water a waning commodity in freshwater wetlands, facilitating the spread of woody shrubs into wetland sedge communities. Working in subtropical Florida peatlands, researchers found that the leaves of these shrub invaders use water less efficiently, resulting in increased loss of water to the atmosphere despite small increases in carbon uptake.

The Impact
Wetlands are critical for storage, filtration, and supply of freshwater. However, the dual impacts of human land use and climate drying due to warmer temperatures place these wetlands at risk, particularly in low-latitude regions where dense human populations are expanding. The feedback between external drying driving shrub encroachment and autogenic drying by those shrubs can degrade wetland habitat quality, biodiversity, and ecosystem function, compromising regional hydrology and carbon storage.

Summary
Studying sawgrass peatlands of south Florida, researchers from Florida Atlantic University quantified differences in plant photosynthetic efficiency and canopy structure between the historic dominant sedge and encroaching native willow to determine the degree to which vegetation carbon and water cycling is altered by shifts in community dominance. Leaf gas exchange of both carbon dioxide (plant photosynthetic uptake) and water (plant transpiration release) was greater for willow, which also used water less efficiently during photosynthesis (greater water loss per carbon gain). Additionally, the willow’s spreading, multitiered branch growth pattern produced more than double the leaf area index (leaf area per ground area). When scaled to the landscape, the elevated water loss rate and leaf density result in substantial increases in wetland water loss through transpiration with even small spatial extent of shrubs. Autogenic drying of wetlands may also accelerate litter and soil decomposition by increasing aerobic conditions, further compromising the health of these peatlands.  

Contacts (PI)
Brian Benscoter
Florida Atlantic University
Brian.Benscoter@fau.edu  
(BER PM)
Daniel Stover and Jared DeForest
SC-23.1
Daniel.Stover@science.doe.gov, 301-903-0289; and Jared.DeForest@science.doe.gov, 301-903-1678

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program (DE-SC0008310), with site data and access provided by the St. Johns River Water Management District.

Publication
Budny, M. L., and B. W. Benscoter. 2016. “Shrub Encroachment Increases Transpiration Water Loss from a Subtropical Wetland,” Wetlands 36(4), 631-38. DOI: 10.1007/s13157-016-0772-5. (Reference link)

Topic Areas:

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



Field measurement of willow leaf gas exchange. [Image courtesy Michelle Budny, Florida Atlantic University]



Willow invading an herbaceous sawgrass community. [Image courtesy Brian Benscoter, Florida Atlantic University]



May 09, 2016

Model-Guided Field Experiments: Ecosystem CO2 Responses in an Australian Eucalypt Woodland

Multimodel a priori predictions for ecosystem CO2 responses in interaction with nutrient and water limitation.

The Science 
Quantitative model projections were made for the recently established Eucalyptus Free-Air CO2 Enrichment (EucFACE) experiment in Australia. Model simulations were designed to evaluate the experiment data as they are collected and to identify key measurements that should be made to discriminate among competing model assumptions.

The Impact
Knowledge of the causes of variation among models is now guiding data collection in the experiment, with the expectation that the guided experimental data collection will optimally inform future model improvements.

Summary
A major uncertainty in Earth system models is the response of terrestrial ecosystems to rising atmospheric carbon dioxide (CO2) concentration, particularly in nutrient-limited environments. The EucFACE experiment, established in a nutrient- and water-limited woodland, presents a unique opportunity to address uncertainty in Earth system models, but can best do so if key model uncertainties have been identified in advance. Researchers applied seven representative vegetation models to simulate a priori possible outcomes from EucFACE. Simulated responses to elevated CO2 of annual net primary productivity (NPP) ranged from 0.5% to 25% across models. The simulated NPP reduction during a low-rainfall year varied even more widely than the CO2 response—from 24% to 70%. Key processes where assumptions caused disagreement among models included nutrient limitations to growth, feedbacks to nutrient uptake, autotrophic respiration, and the impact of low soil moisture availability on plant processes.

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

(PI Contact)
Anthony Walker
Environmental Sciences Division, Climate Change Science Institute
Oak Ridge National Laboratory
walkerap@ornl.gov

Funding
The National Climate Change Adaptation Research Facility (NCCARF) and Primary Industries Adaptation Research Network (PIARN) supported this project and travel for the participants to Sydney, Australia. Support was provided via EucFACE as an initiative supported by the Australian Government through the Education Investment Fund and the Department of Industry and Science, in partnership with the University of Western Sydney. Research support came from the Australian Research Council; U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research; and European Community's Seventh Framework Programme (FP7 2007-2013) under grant agreement 238366 (Greencycles II).

Publication
Medlyn, B. E., et al. 2016. “Using Models to Guide Field Experiments: A Priori Predictions for the CO2 Response of a Nutrient- and Water-Limited Native Eucalypt Woodland,” Global Change Biology 22, 2834-51. DOI: 10.1111/gcb.13268. (Reference link)

Related Link
Data

Topic Areas:

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


May 04, 2016

Permafrost Metaomics and Climate Change

A review of various molecular omics studies on permafrost microbial ecology under a changing climate.

The Science
Permanently frozen soil, or permafrost, covers a large portion of Earth’s terrestrial surface, and, as permafrost thaws, previously protected organic matter becomes available for microbial degradation. Microbes that decompose soil carbon produce carbon dioxide and other greenhouse gases, contributing substantially to climate change. A recent review summarizes the current information from various molecular omics studies on permafrost microbial ecology and explores the relevance of these insights to current understanding of the dynamics of permafrost loss due to climate change.

The Impact
Application of high-throughput sequencing and other omics technologies is enabling the study of permafrost microbial communities and providing high-resolution information about community composition and function in a variety of permafrost locations.

Summary
Permafrost is highly heterogeneous, and the impacts of thaw differ dramatically depending on geography, biochemistry, and microbial residents. A recent review summarizes the current state of knowledge about microbial ecology both within permafrost and in the soil layers activated as permafrost thaws, with an emphasis on the use of modern, high-throughput sequencing technologies to understand permafrost-associated microbial communities and their response to climate change. Understanding of the microbial mechanisms controlling greenhouse gas emissions is in its infancy. Metagenomics must be coupled with enhanced measurements of geochemistry and microbial processes to develop a comprehensive understanding of microbial function and activity in permafrost. Predictive understanding will require information generated by both laboratory-based experiments and long-term in situ studies. In the near future, it is imperative for knowledge generated by metagenomics and other omics approaches to be incorporated into climate models to fully integrate microbiology, geochemistry, geophysics, and hydrology for a better representation of Arctic ecosystems.

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

(PI Contact)
Neslihan Tas
Lawrence Berkeley National Laboratory
ntas@lbl.gov; 510-517-4035

Funding
This work was supported in part by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science (TES) program, under contract number DE-AC02-05CH11231. The authors acknowledge additional financial support from the Microbiomes in Transition (MinT) Initiative at Pacific Northwest National Laboratory, under contract number DE-AC05-76LO1803; DOE Next-Generation Ecosystem Experiment-Arctic (NGEE-Arctic) project; Danish Center for Permafrost (CENPERM); California State University Program for Education and Research in Biotechnology (CSUPERB) New Investigator Grant program; National Aeronautics and Space Administration Exobiology Program (award number NNX15AM12G), DOE Office of Biological and Environmental Research (award number DE-SC0004632); and University of Arizona Technology and Research Initiative Fund, through the Water, Environmental and Energy Solutions Initiative.

Publications
Mackelprang, R., S. R. Saleska, C. S. Jacobsen, J. K. Jansson, and N. Tas. 2016. “Permafrost Meta-Omics and Climate Change,” Annual Review of Earth and Planetary Sciences 44, 439-62. DOI: 10.1146/annurev-earth-060614-105126. (Reference link)

Topic Areas:

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


April 20, 2016

Vast Underground Network of Fungi Detected from Space

Tree-mycorrhizal associations detected remotely from canopy spectral properties.

 The Science  
Researchers used satellite measurements of forest canopies to detect belowground fungal associations with trees across landscapes, testing the findings with 130,000 trees throughout the United States.

The Impact
Nearly all tree species associate with only one of two types of mycorrhizal fungi—arbuscular mycorrhizal (AM) fungi or ectomycorrhizal (ECM) fungi. AM- and ECM-dominated forests have distinct nutrient economies, so detection and mapping of these fungi can provide key insights into fundamental ecosystem properties.

Summary
Hidden belowground is a vast network of fungi that operates in a complex economy within forests, scavenging for nutrients and trading them to trees for carbon sugars. Researchers in a Department of Energy-supported study figured out how to detect this underground network from space. Understanding how different forests get their nutrients is critical to predicting how forests may grow—or be growth-stunted due to lack of nutrients—into the future. The type of mycorrhizal fungi is a key piece of that puzzle in determining how forests will respond to future changes in climate, carbon dioxide, water, and temperature. Scientists have known for many years which tree species associate with which fungi, but mapping every single tree species across large scales such as landscapes or continents has not been possible. The researchers used Landsat satellite measurements of forest canopies to detect mycorrhizal associations. They gathered data from 130,000 trees throughout the United States to test their approach, finding that they could predict 77% of the differences in mycorrhizal associations known on the ground from satellite observations alone.

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

(PI Contact)
Joshua B. Fisher
University of California, Los Angeles; Jet Propulsion Laboratory
joshbfisher@gmail.com, 323-540-4569

Funding
Funding for the remote sensing analysis was provided by the U.S. Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program; National Science Foundation Ecosystem Science Program; and Indiana University.

Publications
Fisher, J. B., S. Sweeney, E. R. Brzostek, T. P. Evans, D. J. Johnson, J. A. Myers, N. A. Bourg, A. T. Wolf, R. W. Howe, and R. P. Phillips. 2016. “Tree-Mycorrhizal Associations Detected Remotely from Canopy Spectral Properties,” Global Change Biology 22(7), 2596-2607. DOI: 10.1111/gcb.13264. (Reference link)

Topic Areas:

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


March 17, 2016

Assessing Earthquake-Induced Tree Mortality in Temperate Forest Ecosystems

A case study looks at the impact of earthquakes and forest dynamics in Wenchuan, China.

The Science
Earthquakes represent a significant driver to forest carbon dynamics. Using a newly developed approach for evaluating post-earthquake disturbance, this study estimates how much biomass carbon loss was associated with the 2008 Wenchuan earthquake in China.

The Impact
This study found that the committed forest biomass carbon loss associated with the May 12, 2008, Wenchuan earthquake (M=7.9) in China was 10.9 Tg C, with the highest tree mortality observed along the fault zone. These findings suggest that earthquake-induced biomass carbon loss should be included in estimating forest carbon budgets.

Summary
Earthquakes can produce significant tree mortality and consequently affect regional carbon dynamics. Unfortunately, detailed studies quantifying the influence of earthquakes on forest mortality are rare. This study assesses the committed forest biomass carbon loss associated with the 2008 Wenchuan earthquake in China with a synthetic approach that integrates field investigation, remote-sensing analysis, empirical models, and Monte Carlo simulations. The newly developed approach significantly improved the forest disturbance evaluation by quantitatively defining the earthquake impact boundary and detailed field survey to validate the mortality models. Based on this approach, a total biomass carbon of 10.9 Tg C was lost in the Wenchuan earthquake, which offset 0.23% of the living biomass carbon stock in Chinese forests. Tree mortality was highly clustered at the epicenter, declining rapidly with distance away from the fault zone. These findings suggest that earthquakes represent a significant driver to forest carbon dynamics, and the earthquake-induced biomass carbon loss should be included in estimating forest carbon budgets.

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

PI Contact
Robinson Negron-Juarez, robinson.inj@lbl.gov

Funding
This study was funded jointly by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA05050407) and the National Natural Science Foundation of China (41371126). Additional support came from the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Contract Number DE-AC02-05CH11231, as part of the Next-Generation Ecosystem Experiments–Tropics project and Regional and Global Climate Modeling program.

Publications
Zeng, H., et al. “Assessing earthquake-induced tree mortality in temperate forest ecosystems: A case study from Wenchuan, China.” Remote Sens. 8(3), 252 (2016). [DOI:10.3390/rs8030252]. (Reference link)

Topic Areas:

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


March 16, 2016

Accelerated Plant Metabolism May Not Speed Up Climate Change as Much as Anticipated

Plant respiration can acclimate to altered temperatures.

The Science  
A long-term study found that, over time, plants can adjust their metabolic rate to reduce the amount of carbon dioxide (CO2) returned to the atmosphere due to warming.

The Impact
Climate change impacts many aspects of Earth’s ecosystems, often in ways that can either slow or accelerate climate change. In a warming world, the return of CO2 to the atmosphere, via plant respiration, was expected to increase with temperature. This study found that plants growing in warmer conditions made adjustments that kept their metabolism on a stable trajectory, eliminating 80% of the possible “extra” carbon flux that would be released by nonacclimatized plants. If such responses are general, the acceleration of climate change by heightened plant respiration in a warmer world will be much smaller than anticipated by theory or Earth system models.

Summary
Plant respiration results in an annual CO2 flux to the atmosphere that is six times as large as that due to the emissions from fossil fuel burning, so changes in either will impact future climate. As plant respiration responds positively to temperature, a warming world may result in additional respiratory CO2 releases and, hence, further atmospheric warming. Plant respiration can acclimate to altered temperatures (e.g., by downward reduction of their entire temperature-response curve in warmer conditions), weakening the positive feedback of plant respiration to rising global air temperature. However, lack of evidence on long-term (weeks to years) acclimation to climate warming in field settings currently hinders realistic predictions of respiratory release of CO2 under future climatic conditions. To address this knowledge gap, a study was conducted from 2009 to 2013 to assess the acclimation capacity of more than 1,200 individuals of 10 dominant North American boreal and temperate tree species grown in ambient and warmed (+3.4 °C) plots in a unique open-air warming experiment in both open and understory forest habitats at two sites (~150 km apart) at the boreal-temperate forest ecotone in Minnesota, USA. For 1,620 leaves of these individuals, respiration was measured from 12 °C to 37 °C. Results found strong acclimation of leaf respiration to both experimental warming and seasonal temperature variation for juveniles of all 10 species. Plants grown and measured at temperatures 3.4 °C above ambient increased leaf respiration by 5% on average compared to plants grown and measured at ambient temperatures; without acclimation, these increases would have been 23%. Thus, acclimation eliminated 80% of the increase in leaf respiration expected of nonacclimated plants. Acclimation of leaf respiration per degree temperature change was similar for experimental warming and seasonal temperature variation. Moreover, the observed increase in leaf respiration per degree increase in temperature was less than half as large as the average reported for prior studies, which were conducted largely over shorter time scales in laboratory settings. If such dampening effects of leaf thermal acclimation occur generally, the increase of terrestrial plant respiration rates in response to climate warming may be less than predicted and, thus, may not raise atmospheric CO2 concentrations as much as anticipated.

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

(PI Contact)
Peter B. Reich
Department of Forest Resources, University of Minnesota
preich@umn.edu

Funding
This research was supported predominantly by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research award number: DE-FG02-07ER64456. Additional support was provided by the Minnesota Agricultural Experiment Station number: MIN-42-030 and number: MIN-42-060; Minnesota Department of Natural Resources; and College of Food, Agricultural, and Natural Resources Sciences and Wilderness Research Foundation, University of Minnesota.

Publications
Reich, P. B., et al. “Boreal and temperate trees show strong acclimation of respiration to warming.” Nature 531, 633–36 (2016). [DOI: 10.1038/nature17142]. (Reference link)

Topic Areas:

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


March 11, 2016

Predicting Biomass Of Hyperdiverse And Structurally Complex Central Amazonian Forests

Reliable biomass estimates require the inclusion of predictors that express inherent variations in species architecture.

The Science  
The hyperdiversity of tropical forests makes it difficult to predict their aboveground biomass levels based on biomass models that generalize across species. In a recent study, researchers employed a virtual forest approach using extensive field data to estimate biomass levels in the central Amazon.

The Impact
Due to the highly heterogenous nature of old-growth forests in structure and species composition, this study found that generic global or pantropical biomass estimation models can lead to strong biases.

Summary
Old-growth forests are subject to substantial changes in structure and species composition due to the intensification of human activities, gradual climate change, and extreme weather events. Trees store circa 90% of the total aboveground biomass (AGB) in tropical forests, and precise tree biomass estimation models are crucial for management and conservation. In the central Amazon, predicting AGB at large spatial scales is a challenging task due to the heterogeneity of successional stages, high tree species diversity, and inherent variations in tree allometry and architecture. The researchers parameterized generic AGB estimation models applicable across species and a wide range of structural and compositional variation related to species sorting into height layers as well as frequent natural disturbances. They used 727 trees from 101 genera and at least 135 species harvested in a contiguous forest near Manaus, Brazil. Sampling from this dataset, the researchers assembled six scenarios designed to span existing gradients in floristic composition and size distribution to select models that best predict AGB at the landscape level across successional gradients. They found that good individual tree model fits do not necessarily translate into reliable AGB predictions at the landscape level. Predicting biomass correctly at the landscape level in hyperdiverse and structurally complex tropical forests requires the inclusion of predictors that express inherent variations in species architecture. Reliable biomass assessments for the Amazon basin still depend on the collection of allometric data at the local and regional scales and forest inventories including species-specific attributes, which are often unavailable or estimated imprecisely in most regions.

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

PI Contacts
Robinson Negron-Juarez, robinson.inj@lbl.gov
Jeffrey Q. Chambers, jchambers@lbl.gov

Funding
This study was financed by the Brazilian Council for Scientific and Technological Development (CNPq) within the projects Piculus, INCT Madeiras da Amazônia, and Succession after Windthrows (SAWI) (Chamada Universal MCTI/No 14/2012, Proc. 473357/2012-7), and supported by the Max Planck Institute for Biogeochemistry within the Tree Assimilation and Carbon Allocation Physiology Experiment (TACAPE). Further support was provided by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under contract number DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments–Tropics project and Regional and Global Climate Modeling program.

Publications
Magnabosco Marra, D., et al. “Predicting biomass of hyperdiverse and structurally complex central Amazonian forests: A virtual approach using extensive field data.” Biogeosciences 13, 1553–70 (2016). [DOI:10.5194/bg-13-1553-2016]. (Reference link)

Topic Areas:

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


March 02, 2016

Climate Change Affects How Soil Bacteria Breathe

A long-term experiment shows that climate shifts produce changes in soil bacteria functioning.

The Science
Understanding how climate change affects the way carbon cycles in and out of the soil is critical for predicting future changes in the carbon cycle, from ecosystem to global scales. This study capitalized on a long-term experiment in which mountain soils were transplanted between a hotter, drier lower elevation and a cooler, moist upper elevation to examine their response to climate change. The unprecedented 17-year length of this experiment is important because short-term experiments are not sufficient to adequately characterize all the ecosystem responses in slow-responding soils.

The Impact
Soils store an enormous amount of carbon globally, and arid land soils are considered particularly sensitive to the effects of climate change. Little is known, however, about how these soils might react as the climate changes, and long-term experiments are extremely rare. Because humans depend on soils for stabilizing carbon against greenhouse gas emissions, cropland production, and a wide variety of other ecosystem services, understanding the effects of climate change on soil is important. Climate change can alter soil physical structure, the composition of microbial communities that reside in soil, amount of carbon that soil can store, and the respiration response.

Summary
A research team, including Department of Energy (DOE) scientists at Pacific Northwest National Laboratory (PNNL), PNNL’s Joint Global Change Research Institute, and a U.S. Department of Agriculture researcher at Washington State University, transplanted soils between two elevations of semi-arid Rattlesnake Mountain, located in eastern Washington state. They chose sites separated by 500 m of elevation with similar plant species and soil types, but very different temperature and rainfall patterns. This experiment was initiated in 1994; 17 years later the team resampled the transplanted soils and controls, measuring carbon dioxide (CO2) production, temperature response, enzyme activity, and bacterial community structure. After incubating the soils for 100 days, they found that transplanted soils (i.e., soils that had been moved between the two sites in 1994) respired roughly equal cumulative amounts of carbon as the nontransplanted soils. Soils transplanted from the hot, dry lower site to the cooler, wetter upper site exhibited almost no respiratory response to temperature—as the temperature rose, they barely responded—but soils originally from the upper cooler site respired at higher rates. However, the bacterial community structure of transplants did not change. These findings show that the climate changes experienced by the transplanted soils prompted significant differences in microbial activity, but no observed change to bacterial structure. These results support the idea that environmental shifts can influence soil carbon through metabolic changes in the soil microbial population, and that those microbes, responsible for the soil-to-atmosphere CO2 flux, may be constrained in surprising ways.

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

(PI Contact)
Vanessa Bailey
Pacific Northwest National Laboratory
Vanessa.Bailey@pnnl.gov, 509-371-6965

Funding
This research was supported by DOE’s Office of Science, Office of Biological and Environmental Research (BER) as part of the Terrestrial Ecosystem Science program and the Signature Discovery Initiative at PNNL. Carbon analyses were performed at the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility sponsored by BER and located at PNNL.

Publication
Bond-Lamberty, B., et al. “Soil respiration and bacterial structure and function after 17 years of a reciprocal soil transplant experiment.” PLOS ONE 11(3), e0150599 (2015). [DOI:10.1371/journal.pone.0150599]. (Reference link)

Topic Areas:

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


February 26, 2016

Leaf Development and Demography Explain Photosynthetic Seasonality in Amazon Evergreen Forests

Cameras show how synchronized birth and death of leaves in the dry season drive increases in photosynthesis and reconcile ground- and satellite-based observations.

The Science  
Scientists used special tower-mounted cameras to discover that synchronization of leaf birth and death in evergreen forest trees across broad areas of the Brazilian Amazon is the cause of strong dry season increases in tropical forest photosynthesis. Furthermore, careful re-analysis of satellite data shows that, contrary to previous reports indicating that dry season increases in Amazon forest greenness may be an artifact of sun-sensor geometry problems, satellite observations do in fact show statistically significant dry-season greenup.

The Impact
These findings about how forests regulate their seasonal “breathing in” of atmospheric carbon dioxide help reconcile the seeming discrepancy between large seasonal changes in photosynthesis seen from towers on the ground versus the smaller changes in “greenness” seen from satellites in space. These findings will also help scientists better understand how climate influences these forests and more accurately predict how they will respond to future climate change.

Summary
In evergreen tropical forests, the extent, magnitude, and controls on photosynthetic seasonality are poorly resolved and inadequately represented in Earth system models. Combining camera observations with ecosystem carbon dioxide fluxes at forests across rainfall gradients in the Amazon, this work shows that aggregate canopy phenology, not seasonality of climate drivers, is the primary cause of photosynthetic seasonality in these forests. Specifically, synchronization of new leaf growth with dry season litterfall shifts canopy composition toward younger, more light-use efficient leaves, explaining large seasonal increases (~27%) in ecosystem photosynthesis. Coordinated leaf development and demography thus reconcile seemingly disparate observations at different scales and indicate that accounting for leaf-level phenology is critical for accurately simulating ecosystem-scale responses to climate change.

Contacts (BER PM)
Daniel Stover, SC-23/1, daniel.stover@science.doe.gov, 301-903-0289; and Jared DeForest, SC-23.1,
jared.deforest@science.doe.gov, 301-903-1678

(PI Contact)
Scott Saleska
Associate Professor, Ecology and Evolutionary Biology, University of Arizona
saleska@email.arizona.edu, 520-461-3330

Funding
Funding was provided by the National Science Foundation’s Partnerships for International Research and Education (0730305); National Aeronautics and Space Administration’s Terra-Aqua Science program (NNX11AH24G); and GOAmazon project, funded jointly by the U.S. Department of Energy (DE-SC0008383) and Brazilian state science foundations in Sao Paulo state (FAPESP) and Amazônas state (FAPEAM).

Publications
Wu, J., et al. “Leaf development and demography explain photosynthetic seasonality in Amazon evergreen forests.” Science 351, 972–76 (2016). [DOI: 10.1126/science.aad5068]. (Reference link)
Saleska, S. R., et al. “Dry–season greening of Amazon forests.” Nature 531, E4–E5 (2016). [DOI: 10.1038/nature16457]. (Reference link)

Related Links
www.saleskalab.org

Topic Areas:

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


February 26, 2016

Nitrogen Availability Increases in a Tundra Ecosystem During Experimental Permafrost Thaw

Plant access to an essential nutrient increases under warmed conditions.

The Science
Researchers warmed a tundra ecosystem in Alaska’s interior for 5 years with a novel experimental method. With this method, the researchers were able to warm the deep soil and degrade the permafrost, as well as document increases in plant access to soil nitrogen, a key nutrient.

The Impact
Global warming will result in the thaw of perennially frozen soils (permafrost), with releases of carbon to the atmosphere. However, this study’s findings show that increased growth of tundra plants could remove some of this carbon from the atmosphere, thus offsetting, in part, the accelerating feedback to climate change.

Summary
Researchers monitored nitrogen in tundra plants and soils during 5 years of experimental warming to quantify how plant access to soil nitrogen changed during permafrost thaw. Nitrogen is a scarce nutrient in high-latitude ecosystems, and plant access to soil nitrogen currently limits plant growth. Within 5 years of warming, plant-available nitrogen in soils increased. Warmed plants were able to grow larger and take up more carbon from the atmosphere than their unwarmed (control) neighbors. Though the study showed that plant biomass increased with warming, it is unlikely that the observed increase in plant carbon storage will be greater than losses of permafrost carbon at this site. In sum, plant carbon uptake offsets, in part, carbon releases from soils, but the system remains a net source of carbon to the atmosphere as a result of permafrost thaw and thus contributes toward accelerating climate change.

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

PI Contact
Edward A. G. Schuur
Center for Ecosystem Sciences and Society, Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011; Ted.Schuur@nau.edu

Funding
This work was supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science program; National Science Foundation CAREER program; National Parks Inventory and Monitoring Program; National Science Foundation Bonanza Creek LTER program; National Science Foundation Office of Polar Programs; and a Discover Denali Research Fellowship awarded to V. Salmon.

Publications
Salmon, V. G., et al. “Nitrogen availability increases in a tundra ecosystem during 5 years of experimental permafrost thaw.” Glob. Change Biol. 22(5), 1927–41 (2015). [DOI:10.1111/gcb.13204]. (Reference link)

Topic Areas:

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


February 19, 2016

Capturing Detailed Dynamics of Tundra Polygonal Structures Using Statistical Modeling Methods

High-resolution predictions of land surface hydrological dynamics are desirable for improved investigations of regional- and watershed-scale processes. Direct deterministic simulations of fine-resolution land surface variables present many challenges, including high computational cost. In a recent Department of Energy (DOE)-supported study, statistically based reduced-order modeling techniques were used to facilitate emulation of fine-resolution simulations. An emulator, a Gaussian process regression, was used to approximate fine-resolution four-dimensional soil moisture fields predicted using a three-dimensional surface-subsurface hydrological simulator (PFLOTRAN). A dimension-reduction technique known as “proper orthogonal decomposition” is further used to improve the efficiency of the resulting reduced-order model (ROM). The ROM reduces simulation computational demand to negligible levels compared to the underlying fine-resolution model. In addition, the ROM constructed was equipped with an uncertainty estimate, allowing modelers to construct a ROM consistent with uncertainty in the measured data. The ROM is also capable of constructing statistically equivalent analogues that can be used in uncertainty and sensitivity analyses. The technique was applied to four polygonal tundra sites near Barrow, Alaska, that are part of DOE’s Next-Generation Ecosystem Experiments (NGEE)-Arctic project. The ROM is trained for each site using simulated soil moisture from 1998 to 2000 and validated using the simulated data for 2002 and 2006. The average relative root-mean-square errors of the ROMs are under 1 percent. The study shows that this statistical method successfully captures detailed physics in a computationally affordable way, and may be a suitable approach for modeling complex physical systems such as evolving tundra.

Reference: Liu, Y., G. Bisht, Z. M. Subin, W. J. Riley, and G. S. H. Pau. 2016. “A Hybrid Reduced-Order Model of Fine-Resolution Hydrologic Simulations at a Polygonal Tundra Site,” Vadose Zone Journal 15(2), DOI: 10.2136/vzj2015.05.0068. (Reference link)

Contact: Dorothy Koch, SC-23.1, (301) 903-0105, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

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


February 10, 2016

Data Synthesis in the Community Land Model for Ecosystem Simulation

An approach for extracting fundamental variables from simulated or observed ecosystem data and synthesizing other variables using the fundamental variables.

The Science  
Sampling theories, data-mining technologies, and virtual-sensor concepts were used to analyze the correlation between model parameters and bridge gaps between observation data streams and modeling data streams.

The Impact
It is an effort to use sampling theory, data-mining technologies, and virtual-sensor concepts to analyze the correlation between model parameters [e.g., over 60 parameters for the canopy flux module (temperature, air, ground, vegetation, carbon dioxide concentration, photosynthesis, leaf area index, and vcmax)] and to bridge the gaps between observation data streams and modeling data streams. This study is a key step forward in synthesizing model-required data streams from observation or measurable datasets, so that computational experiments can be constructed for direct model-data comparison.

Summary
This paper presents a data synthesis model to generate ecosystem data in climate simulations. This model is capable of (1) extracting key features of different physical properties in time and frequency domain, and (2) discovering and synthesizing the physical relationships between ecosystem variables in different feature spaces.

Contacts (BER PM)
Daniel Stover, SC-23.1, daniel.stover@science.doe.gov, 301-903-0289; Jared DeForest, SC-23.1, jared.deforest@science.energy.gov, 301-903-1678; and Dorothy Koch, SC-23.1, dorothy.koch@science.doe.gov, 301-903-0105.

(PI Contact)
Dali Wang
Environmental Science Division, Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN 37831
wangd@ornl.gov, 865-241-8679

Funding
The work was supported in part by NSFC grant 61305114, as well as the Terrestrial Ecosystem Science program and Accelerated Climate Modeling for Energy project funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. This work also used computing resources at Oak Ridge National Laboratory.

Publications
He, H., et al. “Data synthesis in the Community Land Model for ecosystem simulation.” J. Comput. Sci. 13, 83–95 (2016). [DOI:10.1016/j.jocs.2016.01.005]. (Reference link)

Topic Areas:

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


January 06, 2016

Carbon Cost of Plant Nitrogen Acquisition

How is ecosystem growth and carbon sequestration limited by insufficient nitrogen?

The Science
Plants take up carbon from the atmosphere and use that carbon for growth, reproduction, and defenses. Researchers found that plants also use that carbon to acquire nitrogen from various sources—approximately 13 percent of useable carbon (net primary production or NPP) is used for nitrogen acquisition globally (2.4 Pg C yr-1).

The Impact
Most global terrestrial biosphere models do not include the carbon cost of nitrogen acquisition, thereby failing to represent nitrogen limitation to plant carbon dynamics. Much of the uncertainty in the modeled predictions of the future land carbon sink is driven by how these models prescribe nutrient constraints on primary production. Incorporation of these dynamics into global models will lead to improved changes in climate predictions.

Summary
A plant productivity-optimized nutrient acquisition model was integrated into one of the most widely used global terrestrial biosphere models, the Community Land Model (CLM). Global plant nitrogen uptake is dynamically simulated in the coupled model based on the carbon costs of nitrogen acquisition from mycorrhizal roots, non-mycorrhizal roots, symbiotic nitrogen-fixing microbes, and remobilization of nutrients from senescing leaves. Mycorrhizal uptake represented the dominant pathway by which nitrogen is acquired, accounting for about 66 percent of the nitrogen uptake by plants. Overall, the coupled model improves the representations of plant growth limitations globally. Such model improvements are critical for predicting how plant responses to altered nitrogen availability (from nitrogen deposition, rising atmospheric carbon dioxide, and warming temperatures) may impact the land carbon sink.

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

(PI Contact)
Joshua B. Fisher
University of California, Los Angeles; Jet Propulsion Laboratory
joshbfisher@gmail.com, 323-540-4569

Funding
Funding was provided by the U.S. Department of Energy, Office of Biological and Environmental Research, Terrestrial Ecosystem Science Program; and the U.S. National Science Foundation’s Ecosystem Science Program.

Publications
Shi, M., J. B. Fisher, E. R. Brzostek, and R. P. Phillips. 2016. “Carbon Cost of Plant Nitrogen Acquisition: Global Carbon Cycle Impact from an Improved Plant Nitrogen Cycle in the Community Land Model,” Global Change Biology 22(3), 1299-1314. DOI: 10.1111/gcb.13131. (Reference link)

Topic Areas:

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