BER Research Highlights

Search Date: August 09, 2020

36 Records match the search term(s):


December 18, 2019

Changes in Northern Alaska’s Land-to-Ocean River Flows

Warming and permafrost thaw is impacting the region’s terrestrial hydrological flows.

The Science
Through a synthesis of available measurements and state-of-the-art hydrological modeling, the research points to significant increases in the proportion of subsurface runoff and cold season discharge across the North Slope of Alaska, changes that are consistent with warming and thawing permafrost.

The Impact
The Alaskan North Slope rivers carry carbon and other nutrients to the lagoon environments that are prominent components of the Beaufort Sea coast. The changing terrestrial inflows and other alterations connected with permafrost thaw may be influencing food web structure within the lagoons.

Summary
Scientists from the University of Massachusetts-Amherst investigated the changing character of runoff, river discharge, and other hydrological elements across the watershed draining the North Slope of Alaska over the period 1981–2010. Field measurements of discharge and other hydrological cycle elements in this region are sparse, requiring a modeling approach to quantify the land-ocean flows and their changing character. This synthesis of observations and modeling reveals significant increases in the proportion of subsurface runoff. Cold season discharge increases are 134% of the long-term average for the North Slope and 215% for the Colville River basin. The simulations point to a significant decline in terrestrial water storage, as losses in soil ice outweigh gains in soil liquid water storage. The timing of peak spring discharge shifted earlier by 4.5 days, consistent with earlier snowmelt thaw. These changes are consistent with warming and thawing permafrost and have implications for water, carbon, and nutrient cycling in coastal environments. The changing terrestrial inflows may be impacting biological productivity within the lagoons, upon which local native communities rely for their subsistence lifestyle.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Michael Rawlins
Associate Director, Climate System Research Center
University of Massachusetts-Amherst
Amherst, MA
rawlins@geo.umass.edu

Funding
This research has been supported by the Office of Biological and Environment Research (BER, grant no. DE-SC0019462 to M. Rawlins), within the U.S. Department of Energy (DOE) Office of Science, and the DOE Next-Generation Ecosystem Experiments (NGEE)–Arctic project of BER’s Terrestrial Ecosystem Science program (D. Nicolsky). Support was also provided by the Beaufort Lagoon Ecosystems Long Term Ecological Research program (BLE LTER), under the National Science Foundation (NSF) Division of Polar Programs (grant no. NSF-OPP-1656026) and the National Aeronautics and Space Administration (NASA, grant no. 80NSSC19K0649). The study involved use of the Permafrost Water Balance Model v3.

Publication
Rawlins, M. A., L. Cai, S. L. Stuefer, and D. Nicolsky. “Changing characteristics of runoff and freshwater export from watersheds draining northern Alaska.” The Cryosphere 13(12), 3337–52 (2019). [DOI:10.5194/tc-13-3337-2019].

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


December 10, 2019

Arctic Soil Governs Whether Climate Change Drives Global Losses or Gains in Soil Carbon

Multiple model forms needed to capture true uncertainty of soil carbon fate in a changing world.

The Science
Organic matter in soils is persistent because of its physical isolation from soil microbes, but the extent to which these protected soil carbon pools may be vulnerable to environmental change remains uncertain. This uncertainty is reflected in projections of soil carbon change simulated by this project’s models, which disagree as to whether soils will gain or lose carbon through the end of this century.

The Impact
The results from this study illustrate that models disagree on the sign and magnitude of global soil changes through 2100, largely because of the divergent responses of Arctic systems. These results reflect different assumptions about the nature of soil carbon persistence and vulnerabilities, underscoring the challenges associated with setting allowable greenhouse gas emission targets that will limit global warming to 1.5°C.

Summary
Soils store carbon, lots of carbon. Because of these large carbon stocks, exchanges of carbon dioxide (CO2) between soils and the atmosphere are large, and the potential responses of soil carbon stocks and fluxes to projected changes in climate are uncertain. The understanding of factors responsible for the persistence of these vast soil carbon stores has changed dramatically, and models need to widely implement these new ideas. The research team, led by the University of Colorado, Boulder, evaluated three models that make different assumptions about factors responsible for persistence of carbon in soils. Their results show that, although the different model formulations produce similar estimates for initial soil carbon stocks, they show large spread in the fate of soil carbon under projected changes in soil temperature, moisture, and plant growth through the end of this century. These results highlight that greater attention is needed to develop and test model formulations that are consistent with observations and understanding—especially in the Arctic, which has large soil carbon stores that are likely to experience rapid change in upcoming decades.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Will Wieder
University of Colorado, Boulder & National Center for Atmospheric Research
Boulder, CO
wwieder@ucar.edu

Funding
This work was supported by the Terrestrial Ecosystem Science (TES) program of the Office of Biological and Environmental Research (BER) under awards TES DE- SC0014374 and BSS DE-SC0016364), within the U.S. Department of Energy (DOE) Office of Science; U.S. Department of Agriculture (USDA) National Institute of Food and Agriculture (NIFA, 2015-67003-23485); DOE BER RUBISCO Science Focus Area (SFA); and National Aeronautics and Space Administration (NASA) Interdisciplinary Science Program (ISP, award number NNX17AK19G). B. Sulman was supported under award NA14OAR4320106 from the National Oceanic and Atmospheric Administration (NOAA) and U.S. Department of Commerce (DOC) and by the Next-Generation Ecosystem Experiments (NGEE)–Arctic project, supported by TES BER, within the DOE Office of Science.

Publications
Wieder, W. R., B. N. Sulman, M. D. Hartman, C. D. Koven, and M. A Bradford. “Arctic soil governs whether climate change drives global losses or gains in soil carbon.” Geophysical Research Letters 46(24), 14486–95 (2019). [DOI:10.1029/2019GL085543].

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


November 25, 2019

Increasing Impacts of Extreme Droughts on Vegetation Productivity Under Climate Change

Multimodel analysis suggests increases in the frequency of extreme droughts and the magnitude of their effects on plant growth.

The Science
This research showed an increasingly stronger impact on terrestrial gross primary production (GPP) by extreme droughts than by mild and moderate droughts over the 21st century. Specifically, the percentage contribution by extreme droughts to the total GPP reduction associated with all droughts was projected to increase from ~28% during 1850–1999 to ~50% during 2075–2099.

The Impact
Even though higher carbon dioxide (CO2) concentrations in future decades can increase GPP, low soil water availability and disturbances associated with droughts could reduce the benefits of such CO2 fertilization. This study conducted the first global analysis to quantify potential impacts of drought on future GPP, an assessment which could guide future modeling and field experiments.

Summary
Terrestrial GPP is the basis of vegetation growth and food production globally and plays a critical role in regulating atmospheric CO2 through its impact on ecosystem carbon balance. In this study, scientists from the Next-Generation Ecosystem Experiments (NGEE)–Tropics project and Los Alamos National Laboratory (LANL) analyzed outputs of 13 Earth system models to show an increasingly stronger impact on GPP by extreme droughts than by mild and moderate droughts over the 21st century. The droughts were defined on the basis of root-weighted plant-accessible water. Due to a projected dramatic increase in the frequency of extreme droughts, the magnitude of globally averaged reductions in GPP associated with extreme droughts was projected to be nearly tripled by the last quarter of this century (2075–2099) relative to that of the historical period (1850–1999) under both high and intermediate greenhouse gas (GHG) emission scenarios. By contrast, the magnitude of GPP reductions associated with mild and moderate droughts was not projected to increase substantially. These drought impacts were widely distributed with particularly high risks for the Amazon, Southern Africa, Mediterranean Basin, Australia, and the southwestern United States. This analysis indicates a high risk of extreme droughts to the global carbon cycle with atmospheric warming; however, this risk can be potentially mitigated by positive anomalies of GPP associated with favorable environmental conditions.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Chonggang Xu
Los Alamos National Laboratory
Los Alamos, NM
cxu@lanl.gov

Funding
This work was funded by (1) the Next-Generation Ecosystem Experiments (NGEE)–Tropics project and the Survival/Mortality project, both sponsored by the Terrestrial Ecosystem Science program of the U.S. Department of Energy’s (DOE) Office of Biological and Environmental Research within the DOE Office of Science; (2) the Laboratory Directed Research and Development program of Los Alamos National Laboratory; and (3) the University of California’s Laboratory Fees Research Program (Grant No. LFR-18-542511). Also used was the DOE Program for Climate Model Diagnosis and Intercomparison (PCMDI), which provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System (GOES) science portals.

Publications
Xu, C., N. G. McDowell, R. A. Fisher, L. Wei, S. Sevanto, E. Weng, and R. Middleton. “Increasing impacts of extreme droughts on vegetation productivity under climate change.” Nature Climate Change 9, 948–53 (2019). [DOI:10.1038/s41558-019-0630-6].

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


November 07, 2019

Distributed Temperature Profiling Method for Assessing Spatial Variability in Ground Temperatures in a Discontinuous Permafrost Region of Alaska

Identification of correspondences between permafrost, soil, topography, and vegetation properties.

The Science
A new strategy called distributed temperature profiling (DTP) was developed for advancing the characterization and monitoring of soil thermal properties. Combining DTP data with co-located topographic and vegetation maps and geophysical data allowed the identification of correspondences between above- and belowground property distribution.

The Impact
The low cost, portability, and ease of deploying the DTP system make this method efficient for investigating the significant variability in and complexity of subsurface thermal and related hydrological regimes. The potential of this method is significant for informing investigations aimed at quantifying permafrost evolution, water infiltration, snowmelt dynamics, evaporation, biogeochemical processes, and hyporheic exchange.

Summary
Soil temperature has been recognized as a property that strongly influences myriad hydro-biogeochemical processes and reflects how various properties modulate the soil thermal flux. In spite of its importance, the ability to acquire soil temperature data with high spatial and temporal resolution and coverage has been limited because of the high cost of equipment, the difficulties of deployment, and the complexities of data management. The developed new strategy, called DTP, enables measurements of soil temperature at an unprecedented number of locations due to its low cost, low impact, and ease of deployment. The DTP system concept was tested by moving the system sequentially across the landscape to identify near-surface permafrost distribution and correspondences with topography and vegetation properties in a discontinuous permafrost environment near Nome, Alaska, during the summer. Results show that DTP enabled high-resolution identification and lateral delineation of near-surface permafrost locations from surrounding zones with no permafrost or deep permafrost table locations overlain by a perennially thawed layer. Further, the DTP data indicated that changes in soil temperatures often correspond to changes in topography, vegetation, and soil moisture. Near-surface permafrost identified in the study area using the DTP data is primarily co-located under topographic highs and under areas covered with graminoids such as grasses and sedges.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Stan D. Wullschleger
Oak Ridge National Laboratory
Oak Ridge, TN
wullschlegsd@ornl.gov

Funding
The Next-Generation Ecosystem Experiments (NGEE)–Arctic project is supported by the Terrestrial Ecosystem Science program of the U.S. Department of Energy (DOE) Office of Biological and Environmental Research within the DOE Office of Science. This NGEE–Arctic research is supported through Contract No. DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory.

Publication
Léger, E., B. Dafflon, Y. Robert, C. Ulrich, J. E. Peterson, S. C. Biraud, V. E. Romanovsky, and S. S. Hubbard. “A distributed temperature profiling method for assessing spatial variability in ground temperatures in a discontinuous permafrost region of Alaska.” The Cryosphere 13(11), 2853–67 (2019). [DOI:10.5194/tc-13-2853-2019].

Topic Areas:

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


November 05, 2019

For Water on the Arctic Tundra, Timing Is Everything

Tracking water through Arctic polygons using isotopes reveals temporal link to meteorology and biogeochemistry.

The Science
Each spring, the Arctic Coastal Plain transforms from a cold and dry, wind-packed snowscape to a green tundra wetland, where a distinctive honeycomb-like pattern of “polygons” covers large areas due to the formation of vertical ice wedges. Researchers are using the isotopic signatures of water in these polygons to track where the surface water is coming from and where it is going during this critical transition period. In addition, researchers are coupling the timing of these hydrological transitions with the import and export of critical nutrients to and from the landscape and with meteorological datasets.

The Impact
Climate modeling efforts require an accurate representation of Arctic tundra hydrology. This work demonstrates the tight coupling of the landscape water balance with biogeochemical cycles and with the landscape energy balance, inferred from meteorological data. By linking critical details like the landscape water balance and biogeochemical cycles to meteorological parameters that are already widely measured and can readily be measured or estimated remotely, this work provides a simple mechanism for the improved representation of tundra landscapes in models, which can range from watershed to global scales.

Summary
Hydrologically significant periods and transitions were identified using changes in the isotopic composition of polygon surface water. By monitoring the changing ratios of oxygen and hydrogen isotopes in surface water, scientists were able to identify the timing of important hydrological transitions—indiscernible by other methods—and compare them to the timing of biogeochemical changes and landscape energy-balance changes. Researchers found that the timing of these isotopically determined hydrological transitions aligned with the characteristic progression of physical changes described by previous literature. Because the timing of these physical changes is readily observed, or deduced from routine meteorological data, this work provides a mechanism for appraising hydrology and biogeochemistry in high-latitude regions where hydrological and biogeochemical datasets are sparse. This study also revealed that different types of polygons hold water from different sources and identifies the likely sources and sinks of various dissolved ions, including important nutrients, to and from the Arctic landscape.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Stan D. Wullschleger
Oak Ridge National Laboratory
Oak Ridge, TN
wullschlegsd@ornl.gov

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

Publications
Conroy, N. A., B. D. Newman, J. M. Heikoop, et al. “Timing and duration of hydrological transitions in Arctic polygonal ground from stable isotopes.” Hydrological Processes 34(3), 749–64 (2019). [DOI:10.1002/hyp.13623].

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


October 16, 2019

Alder Distribution and Expansion Across a Tundra Hillslope: Implications for Local Nitrogen Cycling

Symbiotic nitrogen fixation by alder shrubs influences the availability of a key limiting nutrient in tundra ecosystems.

The Science
Inputs of nitrogen by alder, a deciduous shrub that associates with nitrogen-fixing bacteria, were quantified in two tundra plant communities, and the ecosystem-scale effects on nitrogen cycling were assessed. The results from this study demonstrate that tall alder shrubland communities had high nitrogen inputs that were associated with high levels of available nitrogen in adjacent soils and plant communities. These tall alder shrublands can be identified in satellite and aerial imagery and have expanded their range during the last half century.

The Impact
Aerial imagery collected from 1956 to 2014 indicated that alder shrublands at this study site expanded 40%, and researchers from Oak Ridge National Laboratory (ORNL) and the Next-Generation Ecosystem Experiments (NGEE)–Arctic team calculated that this expansion may have increased nitrogen inputs by 22%. These findings suggest quantifying nitrogen fixation at the landscape scale is feasible and important for predicting future nutrient availability of warming tundra ecosystems.

Summary
Primary productivity of tundra plants is strongly limited by nitrogen availability, so plants capable of symbiotic nitrogen fixation have the potential to alter plant, soil, and microbial interactions in rapidly warming Arctic ecosystems. The ORNL research team, therefore, investigated the impact that alder, a nitrogen-fixing deciduous shrub, has on tundra nitrogen cycling at a hillslope located on Alaska’s Seward Peninsula. The team quantified nitrogen fixation in two distinct alder communities at this site: tall-statured alder shrublands located on well-drained, rocky outcroppings in the uplands and relatively short statured alder savannas located in water tracks along the moist toe slope of the hill. Annual nitrogen fixation rates in alder shrublands were 1.95 ± 0.68 grams of nitrogen (g N) per m2 per year, leading to elevated nitrogen levels in adjacent soils and plants. Alder savannas had lower nitrogen fixation rates (0.53 ± 0.19 g N per m2 per year), perhaps due to low phosphorus availability and poor drainage in highly organic soil profiles underlain by permafrost. In addition to supporting higher rates of nitrogen fixation, alder shrublands had different foliar traits than alder in savannas, providing an opportunity to link estimates of nitrogen fixation to remotely sensed data products. Analysis of historic aerial and satellite imagery showed that the area covered by alder shrublands at this hillslope site has increased by 40% from 1956 to 2014. The team estimates this increase was associated with a 22% increase in nitrogen inputs from fixation. Study results suggest that expansion of alder shrublands has the potential to substantially alter nitrogen cycling in upland tundra regions. An improved understanding of the consequences of nitrogen fixation within nitrogen-limited tundra plant communities will, therefore, be crucial for predicting the biogeochemistry of warming Arctic ecosystems.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Verity G. Salmon, R&D Associate
Oak Ridge National Laboratory
Environmental Science Division; Climate Change Science Institute
Oak Ridge, TN 37831
salmonvg@ornl.gov

Funding
This work is supported (in part) by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725, with the U.S. Department of Energy (DOE) Office of Science and by the Next-Generation Ecosystems Experiments (NGEE)–Arctic project in the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research (BER), within the DOE Office of Science.

Publication
Salmon, V. G., et al. “Alder distribution and expansion across a tundra hillslope: Implications for local N cycling.” Frontiers in Plant Science 10, 1099 (2019). [DOI:10.3389/fpls.2019.01099].

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


October 15, 2019

The Effects of Phosphorus Cycle Dynamics on Carbon Sources and Sinks in the Amazon Region: A Modeling Study Using ELM v1

Model inclusion of phosphorus limitaiton critical for projecting future carbon uptake in tropical ecosystems.

The Science
Current model simulations using version 1 of the Energy Exascale Earth System (E3SM) land model (ELM v1) show that the consideration of phosphorus availability leads to a smaller carbon sink associated with a carbon dioxide (CO2) fertilization effect and lower carbon emissions resulting from land-use and land-cover changes (LULCC). These simulations suggest phosphorus limitation would significantly reduce the carbon sink associated with CO2 fertilization effects through the 21st century.

The Impact
This study suggests that the Amazon tropical forests may offer less protection against future climate change than suggested by previous modeling studies due to phosphorus limitation.

Summary
The phosphorus-enabled ELM v1 model was used to investigate the effects of phosphorus cycle dynamics and phosphorus limitation on Amazon forest carbon sources and sinks. Historical simulations suggest that the consideration of phosphorus availability leads to (1) a smaller carbon sink associated with the CO2 fertilization effect and (2) lower carbon emissions due to LULCC. When all environmental factors are considered, the study’s model simulations show a smaller carbon sink in the Amazon region when phosphorus limitation is considered. Modeling simulations from the Next-Generation Ecosystem Experiments (NGEE)–Tropics and Oak Ridge National Laboratory used with CO2 concentrations from Representative Concentration Pathway scenarios RCP8.5 and RCP4.5 suggest that phosphorus limitation is critical for projecting future carbon uptake in tropical ecosystems. The predicted carbon sink in Amazon rainforests would be much smaller when phosphorus limitation is considered, suggesting that the Amazon tropical forests may offer less protection against future climate change than suggested by previous modeling studies.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Xiaojuan Yang
Oak Ridge National Laboratory
Oak Ridge, Tenn.
yangx2@ornl.gov

Funding
X. Yang, P. E. Thornton, D. M. Ricciuto, X. Shi, M. Xu, F. M. Hoffman, and R. Norby are supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science. This support includes funding from several BER programs and projects: Terrestrial Ecosystem Science program and its Next-Generation Ecosystem Experiments (NGEE)–Tropics activity; Earth System Modeling Development program (E3SM project), and the Regional and Global Model Analysis program [Reducing Uncertainty in Biogeochemical Interactions Through Synthesis and Computation (RUBISCO) Science Focus Area].

Publication
Yang, X., D. Ricciuto, P. Thornton, X. Shi., M. Xu, F. Hoffman, and R. Norby. “The effects of phosphorus cycle dynamics on carbon sources and sinks in the Amazon region: A modeling study using ELM v1.” JGR Biogeosciences 124(12), 3686–98 (2019). [DOI:10.1029/2019JG005082].

Topic Areas:

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


October 10, 2019

Competitor Sizes and Diffusion Determine Kinetics that Best Approximate Biogeochemical Reaction Rates

ECA kinetics best describes enzymatic depolymerization and microbial substrate uptake.

The Science
The debate on which kinetic formulation should be used to model soil biogeochemical processes (e.g., enzymatic depolymerization and microbial substrate uptake) has accelerated over the past decade. In this project, U.S. Department of Energy (DOE) scientists at Lawrence Berkeley National Laboratory (LBNL) combine the century-old Smoluchowski model of chemical reactions to infer how the sizes of microbes, enzymes, polymer particles, and monomer substrates together determine the mathematical formulations of biogeochemical process rates. They show that neither the popular forward Michaelis-Menten (fMM) kinetics nor the reverse Michaelis-Menten (rMM) kinetics is able to describe these biogeochemical processes that include entities physically varying over orders of magnitude in size. Fortunately, the equilibrium chemistry approximation (ECA) kinetics they recently derived can seamlessly scale over a wide range of biogeochemical reactions.

The Impact
The analysis (1) explains why fMM and rMM kinetics can describe certain biogeochemical processes well, but not others; (2) provides approaches to scale from geometric sizes to kinetic parameters used in soil biogeochemical models; and (3) explains why different sizes of organisms need to be considered explicitly in biogeochemical models.

Summary
Substrate kinetics are essential mathematical tools to model biogeochemistry in various ecosystem processes. However, scientists have been debating which formulations to use to describe the biogeochemical reactions that often involve entities varying over orders of magnitude in physical sizes. The fMM and rMM kinetics are two popular formulations used to interpret and model many biogeochemistry experiments. However, neither of them can perform satisfyingly over the wide range of size scales found in soils. LBNL scientists combined the Smoluchowski model of chemical reactions and a mathematical description of physical sizes to derive relationships that explain why fMM and rMM kinetics performed better in one case and worse in another. In particular, the researchers show that both fMM and rMM kientics are special approximations to the ECA kinetics and that the measurable information of entity sizes and reaction rates provides a good way to parameterize the ECA kinetics. Following their early studies, the team says these results are paving the way to develop a first principles–based model of soil biogeochemistry.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigators
William Riley
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
wjriley@lbl.gov

Jinyun Tang
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
jinyuntang@lbl.gov

Funding
This research is supported as part of the Soil Warming Scientific Focus Area (SFA; Contract No. DE-AC02-05CH11231) at Lawrence Berkeley National Laboratory and the Next-Generation Ecosystem Experiments (NGEE)–Arctic project in the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science.

Publications
Tang, J.-Y., and W. J. Riley. “Competitor and substrate sizes and diffusion together define enzymatic depolymerization and microbial substrate uptake rates.” Soil Biology and Biogeochemistry 139, 107624 (2019). [DOI:10.1016/j.soilbio.2019.107624].

Topic Areas:

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


September 30, 2019

Constraints on Microbial Communities, Decomposition, and Methane Production in Deep Peat Deposits

Temperature is among key factors constraining microbial processes in deep peat deposits.

The Science
This experiment tested the limitations that factors such as pH, nitrogen, and phosphorus may place on peat decomposition. Results showed the peat decomposition and microbial communities were indeed limited by temperature, more so than by nitrogen and phosphorous, but responses were slow to develop even under laboratory conditions.

The Impact
The effects of temperature on peat decomposition and methanogenesis in peatlands may occur over the long term rather than the short term. Other factors such as oxygen, iron, or carbon quality likely play additional roles in constraining peat decomposition responses to temperature.

Summary
Peatlands play outsized roles in the global carbon cycle. Despite occupying a rather small fraction of the terrestrial biosphere (~3%), these ecosystems account for roughly one-third of the global soil carbon pool. This carbon largely consists of undecomposed deposits of plant material (peat) that may be meters thick. The fate of this deep carbon stockpile with ongoing and future climate change is thus of great interest and has large potential to induce positive feedback to climate warming. Recent in situ warming of an ombrotrophic peatland indicated that the deep peat microbial communities and decomposition rates were resistant to elevated temperatures. In this experiment, researchers from Oak Ridge National Laboratory sought to understand how nutrient and pH limitations may interact with temperature to limit microbial activity and community composition. Anaerobic microcosms of peat collected from 1.5 to 2 m in depth were incubated at 6°C and 15°C with elevated pH, nitrogen (NH4Cl), and/or phosphorus (KH2PO4) in a full factorial design. The production of carbon dioxide (CO2) and methane (CH4) was significantly greater in microcosms incubated at 15°C, although the structure of the microbial community did not differ between the two temperatures. Increasing the pH from ~3.5 to ~5.5 altered microbial community structure; however, increases in CH4 production were not significant. Contrary to expectations, nitrogen and phosphorus additions did not increase CO2 and CH4 production, indicating that nutrient availability was not a primary constraint in microbial decomposition of deep peat. These findings indicate that temperature is a key factor limiting the decomposition of deep peat, but other factors such as the availability of oxygen or alternative electron donors and high concentrations of phenolic compounds may also exert constraints.  Continued experimental peat warming studies will be necessary to assess if the deep peat carbon bank is susceptible to increased temperatures over the longer time scales.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Christopher W. Schadt, Senior Scientist
Oak Ridge National Laboratory
Oak Ridge, TN
schadtcw@ornl.gov

Funding
This work was supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science, as part of the Terrestrial Ecosystem Science (TES) Science Focus Area (SFA), and the Spruce and Peatland Responses Under Changing Environments (SPRUCE) project (http://mnspruce.ornl.gov).

Publications
Kluber, L., et al. “Constraints on microbial communities, decomposition and methane production in deep peat deposits.” PLOS ONE 15(2), e0223744 (2020). [DOI:10.1371/journal.pone.0223744].

Related Links

Topic Areas:

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


September 25, 2019

Nitrogen Status Regulates Morphological Adaptation of Marsh Plants to Elevated CO2

“Shrinking Stem” response disappears with nitrogen fertilization.

The Science
Most plants are known to grow faster in an elevated carbon dioxide (CO2) atmosphere, provided they have sufficient nitrogen to use in building plant tissues. A new study found that, while this is true when considering the amount of plant growth per unit of ground area (per meter squared), individual plants may shrink in size in some ecosystems. Researchers conducting the study propose that elevated CO2 can cause clonal plants that reproduce from rhizomes to become denser but smaller and that this result has important consequences for how ecosystems function.

The Impact
Tidal marshes are among the most effective ecosystems on Earth for removing CO2 from the atmosphere and burying it in soils. This process contributes to the ability of marshes to tolerate sea level rise because it adds elevation to the soil surface, maintaining flooding frequency within the marshes’ physiologic limits. A numerical model of sediment deposition in tidal marshes indicates that the increase in stem density will contribute to soil elevation gain, a response that will increase the stability of tidal marshes experiencing accelerated sea level rise.

Summary
It is well known that most C3 plants grow faster in an elevated CO2 atmosphere, provided they have sufficient nitrogen, and that growth at elevated CO2 is preferentially invested in roots to support soil nitrogen acquisition. In ecosystems such as grasslands, which are dominated by herbaceous species, the productivity response is usually measured on an area basis without considering whether increased growth is due to larger individual plants, more individuals per area, or both. This research shows that CO2 stimulation of root growth in a clonal plant species increased biomass on an area basis by 20% but decreased the biomass of individual stems by 16%. This “shrinking stem” response was a consequence of a CO2-induced increase in rhizome production as plants foraged for soil nitrogen, and it disappeared when the ecosystem was fertilized with nitrogen. A numerical model of sediment deposition in tidal marshes indicates that the increase in stem density will contribute to soil elevation gain, a response that will increase the stability of tidal marshes experiencing accelerated sea level rise.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Pat Megonigal
Smithsonian Environmental Research Center
Edgewater, MD 21037-0028
megonigalp@si.edu

Funding
This work was supported by the Office of Biological and Environmental Research (Contract No. DE-SC0008339) within the U.S. Department of Energy Office of Science,  the National Science Foundation (NSF) Long Term Research in Environmental Biology (LTREB) program (DEB-0950080 and DEB-1457100), and the Smithsonian Institution.

Publication
Lu, M., E. R. Herbert, J. A. Langley, M. L. Kirwan, and J. P. Megonigal. “Nitrogen status regulates morphological adaptation of marsh plants to elevated CO2.” Nature Climate Change 9,764–68 (2019). [DOI:10.1038/s41558-019-0582-x].

Topic Areas:

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


September 19, 2019

Plant Root Exudates Increase Methane Emissions Through Direct and Indirect Pathways

Carbon released by plant roots into soil fuels methane production by directly supplying carbon to microbes and by stimulating microbial use of soil organic matter.

The Science
In a plant-growth laboratory experiment conducted with a common wetland sedge (Carex aquatilis) and peat collected from a permafrost-thaw bog, plants were exposed to isotopically labeled carbon dioxide (13CO2) at two time points. Subsequent enrichment of root tissue, rhizosphere soil, and emitted methane (CH4) was used in an isotope mixing model to determine the proportion of plant-derived versus soil-derived carbon supporting methanogenesis. Results showed that carbon exuded by plants was converted to CH4 but also that planted boxes emitted 28 times more soil-derived carbon than was emitted by the unplanted treatments. At the end of the experiment, emissions of excess soil-derived carbon from planted boxes exceeded emissions of plant-derived carbon.

The Impact
In the experiment, an order of magnitude increase in conversion of soil carbon to CH4 was driven by plant growth, which is projected to increase in the boreal region under forecasted climate conditions. The presence of such a large “priming” effect (i.e., the release of carbon by plant roots stimulating a microbial population into breaking down soil organic matter) implies that increased plant productivity potentially could lead to increased conversion of soil carbon to CH4 on climatically relevant scales.

Summary
The largest natural source of CH4 to the atmosphere is wetlands, which produce 20% to 50% of total global emissions. Vascular plants play a key role in regulating wetland CH4 emissions through multiple mechanisms. They often contain aerenchymatous tissues that act as a diffusive pathway for CH4 to travel from the anoxic soil to the atmosphere and for oxygen to diffuse into the soil and enable oxidation of CH4 to CO2. Plants also exude carbon from their roots, stimulating microbial activity and fueling methanogenesis. This study investigated these mechanisms in a laboratory experiment using root boxes containing either C. aquatilis plants, silicone tubes that simulated aerenchymatous gas transfer, or only soil as a control. Methane emissions were over 50 times greater from planted boxes than from control boxes or simulated plants, indicating that the physical transport pathway of aerenchyma was of little importance when not paired with other effects of plant biology. Plants were exposed to 13CO2 at two time points, and the subsequent enrichment of root tissue, rhizosphere soil, and emitted CH4 was used in an isotope mixing model to determine the proportion of plant-derived versus soil-derived carbon supporting methanogenesis. Results showed that carbon exuded by plants was converted to CH4 but also that planted boxes emitted 28 times more soil-derived carbon than was emitted by the other experimental treatments. At the end of the experiment, emissions of excess soil-derived carbon from planted boxes exceeded the emission of plant-derived carbon. This result signifies that plants and carbon exuded by plant roots (i.e., root exudates) altered the soil chemical environment, increased microbial metabolism, and/or changed the microbial community such that microbial utilization of soil carbon was increased (e.g., microbial priming).

Contacts
BER Program Managers
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Jared DeForest, Intergovernmental Personnel Act (IPA) assignment
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division
Environmental System Science

Principal Investigator
Rebecca B. Neumann (University Researcher, Early Career Award)
Associate Professor, Civil & Environmental Engineering
University of Washington, Seattle, WA
rbneum@uw.edu

Funding
This material is based on work supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science, under Award No. DE-SC-0010338. A portion of this research was performed under the Facilities Integrating Collaborations for User Science (FICUS) Program and used resources at the Environmental Molecular Sciences Laboratory (EMSL, grid.436923.9), which is a DOE Office of Science User Facility sponsored by BER and operated under Contract No. DE-AC05-76RL01830. This material is based on work supported by the Office of Science Graduate Student Research (SCGSR) Program of the DOE Office of Science’s Office of Workforce Development for Teachers and Scientists. The SCGSR Program is administered for DOE by the Oak Ridge Institute for Science and Education (ORISE). ORISE is managed by Oak Ridge Associated Universities (ORAU) under Contract No. DE-SC0014664. Students were additionally supported by the University of Washington (UW) College of Engineering Dean’s Fellowship/Ford Motor Company Fellowship, UW Civil & Environmental Engineering Valle Scholarship, UW Mary Gates Scholarship, and Carleton College Kolenkow Reitz Fellowship.

Publication
Waldo, N. B., B. K. Hunt, E. C. Fadely, J. J. Moran, and R. Neumann. “Plant root exudates increase methane emissions through direct and indirect pathways.” Biogeochemistry 145, 213–34 (2019). [DOI:10.1007/s10533-019-00600-6].

Topic Areas:

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


September 03, 2019

The Response of Stomatal Conductance to Seasonal Drought in Tropical Forests

Understanding sources of variation in plant water-use efficiency.

The Science
Stomata regulate carbon dioxide (CO2) uptake by photosynthesis and water loss through transpiration. Accurate model representation of this process, called stomatal conductance, is therefore key for modeling CO2 and water fluxes. The approaches used to represent stomatal conductance in models vary. Current understanding of the drivers of the variation in a key parameter in those models—the slope parameter, which is a measure of plant water-use efficiency—is still limited, particularly in the tropics. Scientists from Brookhaven National Laboratory and the Next-Generation Ecosystem Experiments (NGEE)–Tropics team evaluated the ability of current model formulations to predict observed stomatal conductance, including the inclusion of leaf water potential, and investigated the sources of variation in the slope parameter. They found that inclusion of leaf water potential did not improve model predictions and that model formulations that included vapor pressure deficit performed better than those that relied on relative humidity.

The Impact
Although the value of stomatal slope can have a large impact on simulated carbon and water fluxes, the understanding of what drives the variation in slope parameter is still limited. This study presents a novel integration of rare measurements of gas exchange from the upper canopy of a tropical forest in Panama and a suite of plant traits with analysis that advances the understanding of dominant drivers of stomatal slope variability and identifies a practical, trait-based approach to improve modeling of carbon and water exchange in tropical forests.

Summary
Stomatal slope is inferred from an example stomatal conductance model. For a given CO2 assimilation rate, atmospheric CO2 concentration, and leaf-to-air vapor pressure deficit (collectively, the x-axis), a higher slope means that plants maintain a higher stomatal conductance (y-axis) for a given photosynthetic rate. As such, the slope parameter is an indicator of plant water use efficiency, and a greater slope equates to a lower water use efficiency. The team performed diurnal gas exchange measurements (resulting in background scatterplots) for two example species (Ventilago ferruginea and Terminalia amazonia).

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Alistair Rogers
Brookhaven National Laboratory
Upton, NY
arogers@bnl.gov

Funding
This work was funded by the Next-Generation Ecosystem Experiments (NGEE)–Tropics project in the Terrestrial Ecosystem Science (TES) program of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science.

Publications
Wu, J., S. P. Serbin, K. S. Ely, B. T. Wolfe, L. T. Dickman, C. Grossiord, S. T. Michaletz, A. D. Collins, M. Detto, N. G. McDowell, S. J. Wright, and A. Rogers. “The response of stomatal conductance to seasonal drought in tropical forests.” Global Change Biology 26(2), 823–39. (2020). [DOI:10.1111/gcb.14820].

Topic Areas:

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


August 12, 2019

Ability of Ecosystems to Absorb CO2 from Atmosphere Limited by Nitrogen and Phosphorus Availability in Soils

Nitrogen and phosphorus constrain the CO2 fertilization of global plant biomass.

The Science
To predict the effects of rising atmospheric carbon dioxide (CO2) levels, scientists perform elevated COexperiments at local and regional scales to simulate the response of plants at a global scale. Although there is strong evidence from these experiments that elevated CO2 levels enhance photosynthesis, there are conflicting results for ecosystem-level responses. By globally extrapolating the local results, it becomes evident that the ecosystem-level responses are a function of nutrient availability and nutrient cycling habits.

The Impact
The convergence of past observation with the globally synthesized retrospective predictions of this model supports its future predictions. Despite nutrient limitations, the model indicates that the same key ecosystems will still be responsible for most of the global greening and carbon uptake and forests will continue positive growth trends at CO2 levels expected in 2100. Ultimately, this study highlights the importance of maintaining forests as one of the most important contributions toward limiting global climate change.

Summary
This paper synthesizes observational evidence at local scales and captures a global view of the elevated CO2 effect on plant growth. Data from 138 local elevated COexperiments with 56 potential predictors of CO2 effect were considered for the creation of this model. The model is used to predict plant growth response to elevated CO2 globally. It confirms that soil nutrients are the limiting factors on plant growth and the contrasting growth response of the individual elevated COexperiments can be explained by the differing nutrient cycle habits of various types of forest.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Joshua B. Fisher
University of California, Los Angeles; NASA Jet Propulsion Laboratory
Pasadena, CA
joshbfisher@gmail.com

Funding
The project was funded by the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research (BER) within the U.S. Department of Energy (DOE) Office of Science and by the National Science Foundation’s (NSF) Ecosystem Science Cluster.

Publications
Terrer, C., R. B. Jackson, I. C. Prentice, et al. “Nitrogen and phosphorus constrain the CO2 fertilization of global plant biomass.” Nature Climate Change 9, 684–89 (2019). [DOI:10.1038/s41558-019-0545-2].

Topic Areas:

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


August 08, 2019

Nutrient-Hungry Peatland Microbes Reduce Carbon Loss Under Warmer Conditions

Enzyme production in peatlands reduces carbon lost to respiration under future high temperatures.

The Science
As atmospheric temperatures and carbon dioxide concentrations rise, photosynthesis by plants is expected to increase, leading to more photosynthate released by roots to the soil microbial community. Researchers from Pacific Northwest National Laboratory and Iowa State University examined the response of boreal peatland soils under future high temperatures. The team found that the peatland’s soil microbial communities allocated more carbon to enzyme production in search of phosphorus as temperatures climbed. This diversion of carbon resources could reduce future carbon losses by microbial respiration from the peatland.

The Impact
As boreal peatlands face warmer and drier conditions, it is expected that more carbon will be lost from these carbon-rich soils through increased microbial activity. This study showed that enhanced respiration and concomitant loss of carbon is potentially constrained by nutrient demands of the microorganisms. This tradeoff may help the peatland ecosystem retain soil carbon as temperatures warm.

Summary
Root exudates are carbon compounds, such as sugars and organic acids, which are easily consumed by soil microorganisms. With a warming climate, science suggests that increased photosynthesis by plants could lead to more photosynthate released as root exudates to the soil microbial community. To examine this question, researchers used laboratory incubations to control both temperature and moisture and simulate belowground substrate additions under an accelerated growing season. Results showed that with a moderate increase in temperature, the addition of common root exude compounds in peatlands initially increased carbon lost through microbial respiration above those treatments receiving water only. However, when pushed to future expected high temperatures, additional exudate compounds dampened the amount of additional carbon respired as compared to treatments receiving water only. This reduction in respiration suggests the microorganisms allocated carbon compounds to enzyme production to mine for limited resources instead of respiring carbon. The data also support the idea that boreal peatland microbial communities maintain a more narrow range in function, measured as respiration, across a range in climate conditions. A wide climatic niche in addition to reallocation of carbon resources dampens the magnitude of change in carbon respiration with increasing temperatures.

Contacts
BER

Daniel B. Stover, PhD
Program Manager, Terrestrial Ecosystem Science
Climate and Environmental Sciences Division
daniel.stover@science.doe.gov

PNNL
Kirsten Hofmockel
Biological and Environmental Sciences Directorate
kirsten.hofmockel@pnnl.gov

Funding
This material is based on work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Terrestrial Ecosystem Science (TES) Program, under grant ER65430 to Iowa State University. The SPRUCE experiment is managed by Oak Ridge National Laboratory, which is managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725. 

Publications
Keiser, A. D., M. Smith, S. Bell, and K. S. Hofmockel. “Peatland microbial community response to altered climate tempered by nutrient availability.” Soil Biology and Biochemistry 137(107561), (2019). [10.1016/j.soilbio.2019.107561]

Topic Areas:

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


August 05, 2019

Amazon Forest Response to CO2 Fertilization Dependent on Plant Phosphorus Acquisition

AmazonFACE Model Intercomparison.

The Science
Plant growth is dependent on the availability of nutrients such as nitrogen, phosphorous, and potassium in the soil. Despite the importance of phosphorous in plant processes (e.g., growth and photosynthesis), global Earth system models used in the Coupled Model Intercomparison Project (CMIP5) have not previously included the effects of its availability in studying the global carbon cycle. This study shows that phosphorus availability could greatly reduce the projected CO2-induced carbon sink in Amazon rainforests. This study suggests that the Amazon rainforest response to increasing atmospheric CO2 depends on the ability of trees to upregulate phosphorus acquisition in response to increased carbon availability.

The Impact
Currently, CMIP5 models predict that Amazon rainforests will continue to act as carbon sinks in the future due to the CO2 fertilization effect. However, the role of phosphorus availability (which is impoverished across the Amazon Basin yet controls forest functioning) has not been considered within CMIP5 simulations. This study suggests that the CMIP5 predicted carbon sink would likely be much less due to phosphorus limitation, suggesting that Amazon rainforests may be less resilient to climate change than previously assumed.

Summary
An ensemble of 14 terrestrial ecosystem models was used to simulate the planned free-air CO2 enrichment experiment, AmazonFACE. Model simulations showed that phosphorus availability reduced the projected CO2- induced carbon sink by about 50% compared to estimates from models assuming no phosphorus limitation.

Large variations in ecosystem responses to elevated CO2 among phosphorous-enabled models (ranging from 5 to 140 g C m-2 yr-2 in biomass carbon response) are mainly due to contrasting representations of plant phosphorus use and acquisition strategies among models. This study highlights the importance of phosphorus acquisition and use, including alternative strategies, in Amazon rainforest responses to increasing atmospheric CO2 concentration.

Contacts (BER PM)
Dan Stover and Sally McFarlane (SC-23.1)
daniel.stover@science.doe.gov and sally.mcfarlane@science.doe.gov

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

Funding
DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments–Tropics (NGEE-Tropics) and Energy Exascale Earth System Model (E3SM) programs.

Publication
Fleischer, K., A. Rammig, M. G. De Kauwe, A. P. Walker, T. F. Domingues, L. Fuchslueger, S. Garcia, D. Goll, A. Grandis, M. Jiang, V. E. Haverd, F. Hofhansl, J. Holm, B. Kruijt, F. Leung, B. Medlyn, L. M. Mercado, R. J. Norby, B. C. Pak, B. Quesada, C. von Randow, K. Schaap, O. Valverde-Barrantes, Y. Wang, X. Yang, S. Zaehle, Q. Zhu, and D. Lapola. “Amazon forest responses to CO2 fertilization dependent on plant phosphorus acquisition.” Nature Geoscience 12, 736–41 (2019). [DOI: 10.1038/s41561-019-0404-9]

Topic Areas:

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


August 04, 2019

No Evidence for Triose Phosphate Limitation of Light-Saturated Leaf Photosynthesis Under Current Atmospheric CO2 Concentration

A global analysis of triose phosphate limitation of CO2 assimilation concludes that, contrary to current terrestrial biosphere model representations, the process does not limit CO2 assimilation.

The Science
Photosynthesis is represented in terrestrial biosphere models (TBMs) as the minimum of three processes: carboxylation, electron transport, and triose phosphate utilization (TPU). Model representation of TPU has been shown to be an important limiting process in current TBMs. This study showed that this assumption is false and that TPU is unlikely to limit photosynthesis at current ambient carbon dioxide (CO2) concentration.

The Impact
This work emphasizes the need to better understand TPU limitation and to improve representation of TPU in TBMs. Current representation will result in lower modeled COassimilation, particularly at high latitudes.

Summary
The TPU rate has been identified as one of the processes that can limit terrestrial plant photosynthesis. However, researchers lack a robust quantitative assessment of TPU limitation of photosynthesis at the global scale. As a result, TPU, and its potential limitation of photosynthesis, is poorly represented in TBMs. This research showed that TPU does not limit leaf photosynthesis at the current ambient atmospheric CO2 concentration. Furthermore, data showed that the light-saturated photosynthetic rates of plants growing in cold environments are not more often limited by TPU than those of plants growing in warmer environments. In addition, the work demonstrated that the instantaneous temperature response of TPU is distinct from the temperature response of carboxylation capacity, which is currently used to scale TPU in terrestrial biosphere models.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Alistair Rogers
Brookhaven National Laboratory
Upton, NY
arogers@bnl.gov

Funding
Associated data collection and other contributions by AR were funded by the Next-Generation Ecosystem Experiments (NGEE)–Arctic project, which is supported by the Terrestrial Ecosystem Science program of the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science. 

Publication
Kumarathunge, D. P., B. E. Medlyn, J. E. Drake, A. Rogers, and M. G. Tjoelker. “No evidence for triose phosphate limitation of light-saturated leaf photosynthesis under current atmospheric CO2 concentration.” Plant, Cell & Environment 42(12)3241–52 (2019). [DOI:10.1111/pce.13639].

Topic Areas:

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


July 29, 2019

A Slippery Slope: Soil Carbon Destabilization

Carbon gain or loss depends on the balance between competing biological, chemical, and physical reactions.

The Science
Despite a breadth of research on carbon accrual and persistence in soils, scientists lack a strong, general understanding of the mechanisms through which soil organic carbon (SOC) is destabilized in soils. In a new review article, researchers synthesized principles of soil chemistry, physics, and biology to explain carbon loss in soils. They found that destabilization does not equal stabilization in reverse. Rather, carbon gain or loss depends on the balance among competing biological, chemical, and physical reactions that can be altered by changes in weather and temperature.

The Impact
Rates of soil carbon respiration are increasing with current changes in climate and land use. Therefore, understanding destabilization processes in the soil carbon cycle is imperative. This review informs a more robust understanding of the processes that result in carbon loss and feedbacks to the Earth system. With this context, empirical and computational scientists can target better questions about the potential for soils to affect climate through the carbon cycle, which is important for improving predictive biogeochemical and climate models.

Summary
Most empirical and modeling research on soil carbon dynamics focuses on processes that control and promote carbon stabilization. However, the mechanisms through which SOC is destabilized in soils may be even more important to understand. Destabilization processes occur as SOC shifts from a “protected” or passive state, to an “available” or active state. In the available state, microbes can transform soil carbon to gaseous or soluble forms that are then lost from the soil.

The reviewers, from Pacific Northwest National Laboratory, Dartmouth College, and Oregon State University, considered two well-known phenomena—soil carbon priming and the Birch effect—to show how different mechanisms interact to increase carbon losses. They categorized carbon destabilization processes into three general categories: (1) release from physical occlusion through processes such as tillage, bioturbation, or freeze-thaw and wetting-drying cycles; (2) carbon desorption from soil solids and colloids; and (3) increased carbon metabolism by microbes.

By considering the different physical, chemical, and biological controls as processes that contribute to SOC destabilization, researchers can develop new hypotheses about the persistence and vulnerability of carbon in soils and make more accurate and robust predictions of soil carbon cycling in a changing environment.

Contacts (BER PM)
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

PNNL Contact
Vanessa Bailey, Pacific Northwest National Laboratory, vanessa.bailey@pnnl.gov

Funding
V. L. Bailey was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research as part of the Terrestrial Ecosystem Science program. Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under contract DE-AC05-557 76RL01830. K. Lajtha was supported by National Science Foundation DEB-1257032.

Publication
Bailey, V., C. Hicks Pries, and K. Lajtha. “What do we know about soil carbon?” Environmental Research Letters 14(8), 083004 (2019). [DOI: 10.1088/1748-9326/ab2c11]

Topic Areas:

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


July 15, 2019

Field Evaluation of Gas Analyzers for Measuring Ecosystem Fluxes

How gas analyzer type and correction method impact measured fluxes.

The Science
A side-by-side comparison was conducted of five gas analyzers commonly used to measure ecosystem fluxes of water and carbon dioxide in observation networks such as AmeriFlux. Findings demonstrate that the correction methods applied play a significant role in the measured fluxes.

The Impact
The work describes a new spectral correction method for use in eddy covariance flux calculations that improves upon existing methods across a range of gas analyzers. Due to the variability of fluxes arising solely from the correction method used, researchers emphasize the importance of reporting the correction method as metadata when publishing and sharing flux data.

Summary
The eddy covariance technique (EC) is used at hundreds of field sites worldwide to measure trace gas exchange between the surface and the atmosphere. Data quality and correction methods for EC have been studied empirically and theoretically for many years. The recent development of new gas analyzers has led to an increase in technological options for users. Open-path (no inlet tube) and closed-path (long inlet tube) sensors have long been used, whereas enclosed-path (short inlet tube) sensors are relatively new. Researchers from Lawrence Berkeley National Laboratory and the AmeriFlux Network used five gas analyzers and three sonic anemometers deployed in an agricultural research field in Davis, California. Two different experimental setups were evaluated for 3-month periods. Two established spectral correction methods, as well as a new approach (described in the manuscript), were applied and evaluated for all analyzers. All gas analyzers were found to measure fluxes comparably, if appropriate corrections are applied and quality control measures are taken. Compared to carbon dioxide fluxes, water vapor fluxes were the most variable and sensitive to the gas analyzer type and correction method. Gas analyzers with inlet tubes exhibited larger signal attenuation for water vapor and should be corrected with empirical correction methods. This study provides valuable information for the eddy covariance community to help determine the best sensor, approach, and correction method at sites that meet their specific research questions, as well as potential issues with comparing multiple field sites.

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

(PI Contact)
Sébastien Biraud
Lawrence Berkeley National Laboratory
scbiraud@lbl.gov

Funding
The work was supported by the Office of Biological and Environmental Research within the U.S. Department of Energy’s Office of Science as part of the Terrestrial Ecosystem Science program under contract DEAC0205CH11231 to Lawrence Berkeley National Laboratory.

Publications
Polonik, P., et al.. “Comparison of gas analyzers for eddy covariance: Effects of analyzer type and spectral corrections on fluxes.” Agriculture and Forest Meteorology 272–273, 128–42 (2019). [DOI: 10.1016/j.agrformet.2019.02.010]

Topic Areas:

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


June 17, 2019

Microbial Evolution: Nature Leads, Nurture Supports

(Microbial Evolution: Nature Leads, Nurture Supports

Across ecosystems, microbial traits are preserved along lineages, much like in multicellular organisms, and can improve the development of soil models.

The Science
To better predict how microbes influence how much carbon moves through the water, air, and land, scientists want to compare the influence of evolution (“nature”) and the surrounding climate (“nurture”). Based on an extensive study across environments, from mixed conifer forest to high-desert grassland, the team suggests that microbes are not so different from larger, more complex forms of life. That is, in determining species traits, nature takes the lead, while nurture plays a supporting role.

The Impact
With microbial species, less is known about the relative role of nature versus nurture than desired. Why? Microbes’ small size and great diversity make measuring their traits in nature challenging. This study offers an improved understanding of microbial trait distribution, which influences nutrient cycling, such as growth rate and carbon usage. How bacterial species influence soil carbon cycling may help enhance models to reduce uncertainty when forecasting soil carbon feedbacks to global change.

Summary
How much of a microbe’s makeup and destiny is determined by where it finds itself in the world, and how much is explained by its evolutionary past? While evolutionarily encoded traits (nature) have been more predictive in plants and animals than environmental variation (nurture), the small size and great diversity of microbial species have made it challenging to answer this question in life’s microscopic realm. Now, a team of researchers at West Virginia University, Northern Arizona University, University of Massachusetts Amherst, Lawrence Livermore National Laboratory, and Pacific Northwest National Laboratory used a new approach to determine the traits of microbial species by tracking isotopes into their DNA, indicating rates of carbon assimilation and growth. The team measured these traits in four ecosystems along a gradient in elevation, temperature, and moisture.

They found that, as with plant and animal species, the evolutionary history of soil bacteria (that is, nature) explained more variation in the measured traits than did their local environment (that is, nurture). Evolutionary history explained up to 65 percent of the variation in trait values, while the variation explained by the ecosystem never exceeded 20 percent. Even across vast changes in temperature and precipitation, the traits of microbial species remained relatively consistent. For example, microbial species and families that rapidly used carbon in soil from warm desert grassland showed very similar activity rates when assessed in soil from a comparatively cool and wet forest.

Determining whether nature or nurture has more influence has practical value: if traits are hard-wired by evolution, they are consistent and can be used to make predictions about the natural world.

(Contacts)
BER Program Manager
Dawn Adin
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Biological Systems Science Division (SC-23.2)
Foundational Genomics Research
dawn.adin@science.doe.gov

(Principal Investigator)
Bruce Hungate
Northern Arizona University
Bruce.Hungate@nau.edu

Funding
This work was supported by the Biological Systems Science Division’s Genomic Science program (No. DE-SC0016207) of the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science. It also was supported by the National Science Foundation’s Dimensions of Biodiversity (Nos. DEB-1645596 and DEB-1241094).

Publications
Morrissey, E. M., R. L. Mau, M. Hayer, et al., “Evolutionary history constrains microbial traits across environmental variation.Nature Ecology and Evolution 3, 1064–1069 (2019). [DOI:10.1038/s41559-019-0918-y].

Related Links
Northern Arizona University: Center for Ecosystem Science and Society

Contact: Cathy Ronning, SC-23.2, (301) 903-9549

Topic Areas:

Division: SC-23.2 Biological Systems Science Division, BER


May 21, 2019

Using Remotely Sensed Data to Advance Streamflow Forecasts in Subarctic Watersheds

MODIS fractional snow cover area improves streamflow modeling in undersampled regions of Alaska.

The Science
In the remote and understudied boreal forest of interior Alaska, scientists funded by the Next-Generation Ecosystem Experiments (NGEE)–Arctic project applied remotely sensed snow cover observations to improve snowmelt and streamflow forecasting in river basins with spatially and temporally sparse gaging networks.

The Impact
This paper highlights the challenges of modeling in subarctic environments through assimilating snow remote-sensing data with the discovery that assimilation improves streamflow forecasts in undermonitored systems. The implications of this work have great value for streamflow forecasting and indicate the utility of the remotely sensed fractional snow cover data in the subarctic. Additionally, their improvements to a widely used snow model increase robustness of the hydrological simulations, in support of the U.S. National Weather Service's move toward a physically based National Water Model.

Summary
This study seeks to integrate two different strains of the moderate resolution imaging spectroradiometer (MODIS) remotely sensed fractional snow cover area observations into the Alaska Pacific River Forecast Center’s modeling framework and analyze the results in four watersheds located near Fairbanks, Alaska. This analysis revealed that in well-instrumented systems, such as the Chena River basin, streamflow forecasts were unchanged by the data assimilation. However, for basins with poorly observed precipitation and streamflow, such as the Chatanika River, improving observations of fractional snow cover extent in the models led to a significantly better forecast of streamflow. Because Arctic systems are largely undermonitored, the Chatanika is representative of the challenge in understanding the hydrology of northern rivers, for which improvements in streamflow forecasting are badly needed to mitigate and plan for a changing north.

Contacts (BER PM)
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

(PI Contact)
Katrina E. Bennett
Los Alamos National Laboratory, Earth and Environmental Sciences, Hydrologist and Team Leader
kbennett@lanl.gov

Jessica E. Cherry
Alaska Pacific River Forecast Center
jessica.cherry@noaa.gov

Funding
Alaska Climate Science Center, Natural Science and Engineering Research Council of Canada, GOES-R High Latitude Proving Ground award NA08OAR432075, and U.S. Department of Energy, Office of Science, Biological and Environmental Research program, Next-Generation Ecosystem Experiments (NGEE)–Arctic project.

Publications
Bennett, K. E., J. E. Cherry, B. Balk, and S. Lindsey. “Using MODIS estimates of fractional snow cover area to improve streamflow forecasts in interior Alaska.” Hydrology and Earth System Sciences 23(5), 2439–59 (2019). [DOI: 10.5194/hess-23-2439-2019]

Topic Areas:

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


May 20, 2019

Revealed: The Influence of Microbes on Soil Respiration

Research shows that microbial biomass has a greater influence than expected on how soils react to changes in temperature.

The Science
Millions of microbes living in the soil could influence how soils respond to temperature changes. They also influence the amount of carbon dioxide soils give off or respire. Yet scientists rarely consider these microbes when modeling temperature effects around the world. An international team of scientists analyzed the results of more than two dozen warming experiments to quantify how much these microbes influence soil respiration under various temperatures and in what ways.

The Impact
Increased temperatures often lead to soils giving off more organic carbon. More carbon in the air can in turn increase air temperature. By understanding the influence of microbes living in the soil, scientists can better calculate this carbon-temperature feedback cycle and predict temperature changes more accurately.

Summary
Scientists from Iowa State University, University of Maryland, Pacific Northwest National Laboratory, the Czech Academy of Sciences, and the Environmental Molecular Sciences Laboratory teamed up to review data from 27 warming experiments. These experiments ranged from laboratory studies to observations made at various locations and in various types of soil around the world under temperatures between just above freezing to scorching hot. Based on these studies, the team discovered that, when the mass of microbes decreased, soils were less likely to give off carbon dioxide as temperatures increased. When the mass of microbes increased, soils were more likely to respire carbon dioxide. Changes in respiration rates also varied by type of soil. The results suggest that microbial biomass needs to be explicitly measured and considered in models to calculate changes in temperature and their effect on soil.

BER PM Contact
Paul Bayer
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
DOE Environmental Molecular Sciences Laboratory
paul.bayer@science.doe.gov

PI Contact
Petr Capek
Environmental Molecular Sciences Laboratory
Peter.Capek@pnnl.gov

Funding
This work was supported by the U.S. Department of Energy (DOE),Office of Science, Office of Biological and Environmental Research, Climate and Environmental Sciences Division, including support of the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility, and the Terrestrial Ecosystem Science program.

Publication
Capek, P., R. Starke, K. S. Hofmockel, B. Bond-Lamberty, and N. Hess. “Apparent temperature sensitivity of soil respiration can result from temperature driven changes in microbial biomass.” Soil Biology and Biochemistry 135, 286–93 (2019). [DOI:10.1016/j.soilbio.2019.05.016]

 

Topic Areas:

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


May 13, 2019

Millennial and Fast-Cycling Arctic Soil Carbon are Equally Sensitive to Warming

Radiocarbon-based evidence from a soil warming experiment was used to understand carbon decomposition.

The Science
This study investigated the effects of warming on Arctic soil carbon and showed that decomposition rates of fast-cycling and slow-cycling soil carbon are equally temperature sensitive. The study used an incubation experiment and a novel method for analyzing radiocarbon content to evaluate soil carbon age and decomposability and to disentangle the effects of warming and substrate depletion on carbon mineralization.

The Impact
In soils from Utqiagvik (formerly Barrow), Alaska, ancient soil carbon was highly vulnerable to warming, with no relationship between temperature sensitivity and historical cycling rate. When soils were thawed and oxygen was not limiting, carbon that had been stored for centuries or millennia was poorly protected against microbial decomposition.

Summary
Intact (nonhomogenized) soil samples from Utqiagvik, Alaska, were sequentially incubated at 5°C and 10°C at Lawrence Berkeley National Laboratory. To account for substrate depletion as the experiment progressed, a third incubation was performed at 5°C. Carbon dioxide (CO2) production rates and natural abundance Δ14C of CO2 were measured after each incubation to evaluate vulnerability to warming of slow-cycling and fast-cycling soil carbon pools. Based on Δ14C values from the first incubation, very old soil carbon was readily decomposable when soils were thawed and aerobic. A novel regression technique was used to estimate temperature sensitivities using bulk (measured) CO2 production rates, and rates partitioned with radiocarbon into fast-cycling (carbon age = 50 years) and slow-cycling (carbon age = 5,000 years) pools. No difference in temperature sensitivity was found between fast-cycling and slow-cycling carbon. These findings suggest that mechanisms other than chemical recalcitrance mediate the effect of warming on soil carbon mineralization.

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

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

Funding
This research was conducted through the Next-Generation Ecosystem Experiments– Arctic (NGEE-Arctic) project, which is supported by the Office of Biological and Environmental Research within the U.S. Department of Energy’s Office of Science.

Publications
Vaughn, L. J. S., and M. S. Torn “14C evidence that millennial and fast-cycling soil carbon are equally sensitive to warming.” Nature Climate Change 9, 437–38 (2019). [DOI: 10.1038/s41558-019-0468-y]

Related Links
https://www.nature.com/articles/s41558-019-0483-z

Topic Areas:

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


May 08, 2019

Growth and Opportunities in Networked Synthesis Through AmeriFlux

The AmeriFlux Decadal Synthesis.

The Science
The AmeriFlux project now represents more than 5,000 registered scientists who use AmeriFlux observations for a range of applications, including ecosystem science, modeling, and remote sensing, as well as education and outreach.

The Impact
A team led by Lawrence Berkeley National Laboratory (LBNL) convened the series’ inaugural workshop, focused on emerging topics in decadal synthesis. Forty scientists gathered at LBNL for three days, discussing a range of topics. They identified six emerging themes of interest: (1) decadal ecosystem dynamics, (2) extreme event detection and ecological impact assessment, (3) plant phenological change, (4) methane cycling, (5) synthesis across multiple measurement types, and (6) land surface model-data integration.

Summary
The AmeriFlux community has evolved from a disparate group of collaborators focused on ecosystem carbon budgets to an established and highly organized network dedicated to improving the understanding of ecosystem function and providing observations to the broader scientific community. The growing mountain of observations necessitates a high degree of collaboration and opens opportunities to address questions that were previously unanswerable. Much still needs to be done, however, to improve connections to, and learn from, other networks around the world. The past decade has seen much change, and the community is excited about the progress yet to come.

Contacts
BER Program Manager
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Principal Investigator
Trevor Keenan
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
trevorkeenan@lbl.gov

Funding
The AmeriFlux Management Project (AMP) is supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science. DOE established AMP at Lawrence Berkeley National Laboratory (LBNL) to support the broad AmeriFlux community and the AmeriFlux sites.

Publications
Keenan, T. F., D. J. P. Moore, and A. Desai. “Growth and opportunities in networked synthesis through AmeriFlux.” New Phytologist 222(4), 1685–87 (2019). [DOI:10.1111/nph.15835].

Topic Areas:

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


May 02, 2019

The "One-Point Rapid" Method for Estimating the Capacity for Photosynthetic CO2 Assimilation Must be Used with Caution

Acclimation to saturating light is often required for the method to be effective.

The Science
The gold-standard method for measuring the capacity for photosynthetic carbon dioxide (CO2) assimilation is time consuming. A rapid method to mathematically estimate this capacity from a single measurement rather than a full curve has been celebrated in the literature, but there are several key limitations to the effectiveness of this rapid method, including acclimation to light.

The Impact
The accurate estimation of the capacity for photosynthetic CO2 assimilation is critical for the parameterization of climate models. Employing a rapid “one-point” method can improve model parameterization but only if the results are accurate. Deepening the scientific understanding of the limitations of this method allows appropriate use of the technique.

Summary
The maximum carboxylation capacity of photosynthesis (Vc,max) is usually obtained using a gold-standard photosynthetic CO2 response curve. A rapid one-point method mathematically estimates Vc,max from a single-point measurement of photosynthesis rather than a full response curve, taking only a fraction of the time. Scientists from Brookhaven National Laboratory evaluated the practical application of the one-point method in six species measured both under standard conditions and under conditions that would increase the likelihood of successful estimation of Vc,max. Under standard measurement conditions, the one-point method significantly underestimated Vc,max in four of the six species, providing estimates 21% to 32% below fitted values. They identified three factors that can limit the effective use of the one-point method to accurately estimate Vc,max: (1) limitation of photosynthesis by carboxylation, when the measurement is taken; (2) acclimation of leaves to saturating light conditions prior to measurement; and (3) accurate estimation of leaf respiration. Most critical of these is the requirement for acclimation to saturating light. The requirements vary among species, meaning that the one-point method requires a species-specific understanding of its application and must be used with caution.

Contacts
BER Program Managers
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division (SC-33.1)
Environmental System Science
daniel.stover@science.doe.gov

Jared DeForest, Intergovernmental Personnel Act (IPA) assignment
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Earth and Environmental Systems Sciences Division
Environmental System Science

Principal Investigator
Angela Burnett
Brookhaven National Laboratory
Upton, NY
aburnett@bnl.gov

Institutional Contact
Alistair Rogers
Brookhaven National Laboratory
Upton, NY
arogers@bnl.gov

Funding
This work was supported by the Office of Biological and Environmental Research (BER), within the U.S. Department of Energy (DOE) Office of Science, under Contract No. DE-SC0012704 to Brookhaven National Laboratory and received partial support (e.g., some of the data collection) from the Next-Generation Ecosystem Experiments (NGEE)–Arctic project, which is supported by DOE BER.

Publications
Burnett, A. C., K. Davidson, S. P. Serbin, and A. Rogers. “The ‘one-point method’ for estimating maximum carboxylation capacity of photosynthesis: A cautionary tale.” Plant, Cell & Environment 42(8), 2472–81 (2019). [DOI:10.1111/pce.13574].

Burnett, A. C., K. Ely, K. Davidson, et al. “Evaluation of the one-point method for estimating carboxylation capacity, Barrow, Alaska and Upton, New York, 2018. (2019) Next Generation Ecosystem Experiments Arctic Data Collection, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn. [DOI:10.5440/1506965].

Related Links
Next-Generation Ecosystem Experiments (NGEE)–Arctic: https://ngee-arctic.ornl.gov

Topic Areas:

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


April 13, 2019

Soil Property Variation Drives Large Differences in Tropical Forest Secondary Succession

Nutrient limitations and soil texture differences explained plant biomass variation during secondary succession in tropical forest inventories.

The Science
Scientists at the University of Notre Dame used a new mechanistic vegetation dynamics model based on the Ecosystem Demography (ED2) model, which has been augmented to account for nitrogen and phosphorus limitations of vegetation productivity, explicit soil microbial and enzyme processes, and plant-microbe competition for nutrients (Medvigy et al. 2019). The model realistically represented vegetation differences across tropical forests sites that have very large gradients in vegetation biomass and nutrient availability. The researchers used the model to explain observed variations in vegetation at spatial scales finer than those represented in current Earth system models, implying needed improvements to those models.

The Impact
Current land models applied for large-scale assessments of nutrient controls on vegetation processes have large uncertainties. This study used a mechanistic dynamic vegetation model to demonstrate that soil property variations can be mechanistically linked to plant biomass and composition. Representing geodiversity at sub-gridcell scales is therefore critical for large-scale dynamic vegetation models, such as the Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM) Land Model (ELM)-Functionally Assembled Terrestrial Ecosystem Simulator (FATES) model being developed for the E3SM.

Summary
Observations in tropical forests reveal large variation in biomass and plant composition. In this study, scientists from the University of Notre Dame evaluated whether such variation can emerge solely from realistic variation in a set of commonly measured soil chemical and physical properties. Controlled simulations were performed using a mechanistic model that includes forest dynamics, microbe-mediated biogeochemistry, and competition for nitrogen and phosphorus. Observations from 18 forest inventory plots in Guanacaste, Costa Rica, were used to determine realistic variation in soil properties. In simulations of secondary succession, the across-plot range in plant biomass reached 30% of the mean and was attributable primarily to nutrient limitation and secondarily to soil texture differences that affected water availability. The contributions of different plant functional types to total biomass varied widely across plots and depended on soil nutrient status. In simulations, large variation in plant biomass and ecosystem composition arose mechanistically from realistic variation in soil properties and climate. In general, model predictions can be improved through better representation of soil nutrient processes, including their spatial variation. These results inform ongoing development in DOE’s dynamic vegetation model integrated in E3SM (ELM-FATES).

Contacts (BER PM)

Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

Renu Joseph
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Earth and Environmental Systems Modeling
renu.joseph@science.doe.gov

(PI Contact)
David Medvigy, University of Notre Dame, dmedvigy@nd.edu

Funding
David Medvigy, Bonnie Waring, and Jennifer S. Powers were supported by the U.S. Department of Energy (DOE), Office of Science, Office of Biological and Environmental Research (BER),Terrestrial Ecosystem Science program, award DE-SC0014363. The field plots were maintained by National Science Foundation CAREER grant DEB-1053237 to JSP.

Funding for William J. Riley and Qing Zhu was provided by DOE BER under contract number DE-AC02-05CH11231 as part of the Regional and Global Model Analysis (RGMA) program in the Earth and Environmental Systems Modeling program’s RUBISCO Science Focus Area.

Gangsheng Wang was supported by the Energy Exascale Earth System Model (E3SM) project and the Climate Model Development and Validation (CMDV) project under contract DE-AC05-00OR22725 to Oak Ridge National Laboratory.

Publications
Medvigy, D., G. Wang, Q. Zhu, W. J. Riley, A. Trielweiler, B. Waring, X. Xu, and J. Powers. "Observed variation in soil properties can drive large variation in forest functioning and composition during tropical forest secondary succession." New Phytologist 223(4), 1820–33 (2019). [DOI: 10.1111/nph.15848]

Topic Areas:

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


March 29, 2019

Climate Change Will Result in Large Increase in Methane Emissions in Polygonal Tundra

Methane emissions responded strongly to changes in temperature, atmospheric carbon dioxide, precipitation, and landscape-scale hydrology.

The Science
Scientists from the Next-Generation Ecosystem Experiments (NGEE)–Arctic project used ecosys, a mechanistic three-dimensional ecosystem model, to project how carbon dioxide (CO2) and methane (CH4) emissions at the NGEE–Arctic Utqiagvik polygonal tundra site will change over the 21st century. The model very accurately matched a wide range of NGEE–Arctic observations. CH4 emissions responded strongly to changes in temperature, atmospheric CO2, and precipitation, and they represent large potential radiative feedbacks with climate.

The Impact
Land models predict a wide range of potential permafrost tundra CO2 and CH4 emissions over the 21st century. In this study, a team of scientists from Lawrence Berkeley National Laboratory identified dominant processes responsible for variations of these emissions over time and space. They found that predicted increases in CO2 uptake were offset by large CH4 emissions, and that potential increases in drainage would decrease net CH4 emissions, highlighting the importance of landscape-scale hydrology for 21st century predictions.

Summary
Model projections of CO2 and CH4 emissions in permafrost systems vary widely between land models. In this study, the researchers used ecosys to examine how climate change will affect these emissions in a polygonal tundra site at Utqiagvik (formerly Barrow) Alaska. The model has been thoroughly tested against NGEE–Arctic thermal, hydrological, and biogeochemical observations. During the Representative Concentration Pathway (RCP) 8.5 climate change scenario from 2015 to 2085, rising air temperatures, atmospheric CO2, and precipitation (P) increased net primary productivity consistently with biometric estimates. Concurrent increases in heterotrophic respiration (Rh) were offset by increases in CH4 emissions. Both these increases were smaller if boundary conditions were altered to increase landscape drainage, highlighting the importance of these large-scale hydrological dynamics for carbon cycle predictions.

Contacts (BER PM)
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

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

Funding
This research was supported 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 (NGEE)–Arctic project.

Publications
Grant, R. F., Z. A. Mekonnen, and W. J. Riley. "Modelling climate change impacts on an Arctic polygonal tundra. Part 2: Changes in CO2 and CH4 exchange depend on rates of permafrost thaw as affected by changes in vegetation and drainage." Journal of Geophysical Research-Biogeosciences 125(5), 1323–41 (2019). [DOI: 10.1029/2018JG004645]

Topic Areas:

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


March 29, 2019

Modeling Climate Change Impacts on an Arctic Polygonal Tundra: Rates of Permafrost Thaw Depend on Changes in Vegetation and Drainage

Accounting for 21st century polygonal tundra vegetation changes, and consequent effects on surface energy budgets, slows increases in active-layer deepening.

The Science
University of Alberta and Berkeley Lab researchers used a mechanistic three-dimensional ecosystem model (ecosys) to project how vegetation cover changes in polygonal tundra will interact with soil temperatures and active-layer dynamics (Grant et al. 2019). The model was shown to very accurately match a wide range of Next-Generation Ecosystem Experiments (NGEE)–Arctic observations at the Utqiagvik, Alaska, site. Vegetation and landscape-scale hydrology strongly affect surface energy budgets and thereby active-layer deepening, implying that land models must accurately represent these processes in 21st century simulations.

The Impact
Current land models applied for large-scale assessments of permafrost dynamics have poorly represented many of the processes known to affect these dynamics. In this study, the research team used a mechanistic three-dimensional model to explore the roles that vegetation changes and landscape-scale hydrology over the coming decades will have on soil thermal dynamics. Their results point toward the importance of representing vegetation dynamics (e.g., density and composition) and hydrology at relevant spatial scales, and that doing so will result in smaller changes to soil temperatures and active-layer deepening.

Summary
Model projections of permafrost thaw during the next century diverge widely. This study used ecosys to examine how climate change will affect permafrost thaw in a polygonal tundra at Utqiagvik (formerly Barrow), Alaska. The model was tested against observed diurnal and seasonal variation in energy exchange, soil heat flux, soil temperature (Ts) and active-layer depth (ALD), and interannual variation in observed ALD from 1991 to 2015. During Representative Concentration Pathway (RCP) 8.5 scenario climate change from 2015 to 2085, increases in air temperature and precipitation altered energy exchange by increasing the leaf area index (LAI) of dominant sedge relative to that of moss. Increased carbon dioxide concentrations and sedge LAI imposed greater stomatal control of transpiration and reduced soil heat fluxes, slowing soil warming, limiting increases in evapotranspiration, and thereby causing gradual soil wetting. Larger landscape drainage slowed ALD increases. The predicted rates are closer to those derived from current studies of warming impacts in the region, but were smaller than those of earlier modeling studies, primarily because they did not account for vegetation changes. Therefore, accounting for climate change effects on vegetation density and composition, and consequent effects on surface energy budgets, will cause slower increases in active-layer deepening over the 21st century.

Contacts (BER PM)
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

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

Funding
This research was supported 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 (NGEE)–Arctic project.

Publications
Grant, R. F., Z. A. Mekonnen, and W. J. Riley. "Modelling climate change impacts on an Arctic polygonal tundra. Part 1: Rates of permafrost thaw depend on changes in vegetation and drainage." Journal of Geophysical Research-Biogeosciences 124(5), 1308–22 (2019). [DOI: 10.1029/2018JG004644, 2019]

Topic Areas:

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


March 18, 2019

Theoretical Foundation for Applying Sun-Induced Chlorophyll Fluorescence in Global Photosynthesis Research

An analytical framework is established to guide the observation and modeling of sun-induced chlorophyll fluorescence and its applications in ecosystem science.

The Science
Recent progress in observing sun-induced chlorophyll fluorescence (SIF) provides an unprecedented opportunity to advance photosynthesis research in natural environments. However, an analytical framework to guide SIF studies and integration with the well-developed active fluorescence approaches is lacking. A set of coupled fundamental equations was therefore derived to describe the dynamics of SIF and its relationship with C3 and C4 photosynthesis. These equations show that although SIF is dynamically as complex as photosynthesis, the measured SIF simplifies photosynthetic modeling from the perspective of light reactions by integrating over the dynamic complexities of photosynthesis. Specifically, the measured SIF contains direct information about the actual electron transport from photosystem II to photosystem I, giving a quantifiable link between light and dark reactions. With much-reduced requirements on inputs and parameters, the light reactions-centric, SIF-based biophysical model complements the traditional, dark reactions-centric biochemical model of photosynthesis. The SIF-photosynthesis relationship, however, is nonlinear because photosynthesis saturates at high light while SIF has a stronger tendency to keep increasing as fluorescence quantum yield has a relatively muted sensitivity to light levels.

The Impact
The theory developed in this study clarifies several conflicting issues in the SIF-photosynthesis relationship, provides a solid foundation for SIF research, and points to future research directions.

Summary
Chlorophyll a fluorescence (ChlF) is the emission of red and far-red photons from the excited states of chlorophyll molecules in competition with photochemical and non-photochemical energy uses. It is tightly coupled to photosynthesis at the level of fundamental biochemical and biophysical processes. The feasibility of remotely sensing SIF, which is also referred to as passive ChlF, has stimulated a flurry of research to correlate SIF with gross primary production (GPP) and related variables. This enthusiasm has raised the hope of making concrete progress toward understanding and predicting the dynamics of GPP from canopy to global scales, a recalcitrant challenge that has plagued generations of researchers in ecosystem, plant, and agricultural sciences. However, the precise relationship between SIF and GPP is currently unknown. The theory developed in this study fills this gap. Its application will advance a predictive understanding of several previously underexplored physiological and biophysical processes under natural conditions. Advances can be facilitated by coordinated efforts in plant physiology, remote sensing, and eddy covariance flux observations.

Contact (BER PM)
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

PI Contact
Lianhong Gu  
Oak Ridge National Laboratory, lianhong-gu@ornl.gov

Funding
The U. S. Department of Energy, Office of Science, Office of Biological and Environmental Research

Publication
Gu, L., J. Han, J. D. Wood, C. Y. Y. Chang, and Y. Sun. “Sun-induced Chl fluorescence and its importance for biophysical modeling of photosynthesis based on light reactions.” New Phytologist 223(3), 1179–91 (2019). [DOI: 10.1111/nph.15796]

Topic Areas:

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


February 14, 2019

A Decade of CO2 Enrichment Stimulates Wood Growth by 30%

Synthesis of four long-term, DOE supported, CO2 enrichment experiments show that young temperate forests increase carbon uptake at climate-change relevant timescales.

The Science
A synthesis of long-term, DOE-supported experiments shows that in young temperate forests, tree biomass growth increased by 30 % in response to a decade of CO2-enrichment. This response was predictable with knowledge of the plant production response to CO2, and the relationship of wood production to whole plant production under ambient CO2 conditions.

The Impact
CO2-fertilization is the stimulation of gains in plant biomass by increased atmospheric CO2, which creates a feedback on the rate of increase in atmospheric CO2. The complexity combined with the global and decadal scales of this process means that estimates of the size of the feedback remain uncertain. By synthesizing the longest running experiments in forest or woody ecosystems this study develops understanding of the processes that determine CO2-fertilisation at longer timescales and ecosystem spatial scales.

Summary
Stimulation of photosynthesis by increasing atmospheric CO2 can increase plant production, but at longer timescales, may not necessarily increase plant biomass because all the additional production could be in short-lived tissues such as leaves and fine-roots. An international team of scientists, led by Oak Ridge National Laboratory, analyzed the four decade-long CO2 enrichment experiments in forests that measured total plant production and biomass (including below-ground). Using statistical mixed-models they showed that CO2 enrichment increased biomass increment by 1.05 ± 0.26 kg C m-2 over a full decade. This response was predictable with knowledge of the production response to CO2 (0.16 ± 0.03 kg C m-2 y-1) and the biomass retention rate (slope of the relationship between biomass increment and cumulative production; 0.55 ± 0.17) which was independent of CO2. An ensemble of terrestrial ecosystem models failed to predict both terms correctly, but with different reasons among sites. These results demonstrate that a decade of CO2 enrichment stimulates live-biomass increment in temperate, early-succession, forest ecosystems. CO2-independence of the biomass retention rate highlights the value of understanding ambient conditions for interpreting CO2 responses.

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

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

Funding
DOE Office of Science Biological and Environmental Research, Terrestrial Ecosystem Science, and Free Air CO2 Enrichment Model Data Synthesis (FACE-MDS).

Publications
Walker, A. P., et al. “Decadal biomass increment in early secondary succession woody ecosystems is increased by CO2 enrichment.” Nature Communications 10, 454 (2019) [DOI: 10.1038/s41467-019-08348-1].

Related Links
Paper
https://facedata.ornl.gov/facemds/
https://data.ess-dive.lbl.gov/view/doi:10.15485/1480328
https://data.ess-dive.lbl.gov/view/doi:10.15485/1480325
https://data.ess-dive.lbl.gov/view/doi:10.15485/1480327

Topic Areas:

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


February 14, 2019

Terrestrial Biosphere Models May Overestimate Arctic CO2 Assimilation if They Do Not Account for the Effect of Low Temperature on Photosynthesis

Reduced ability to utilize light at low temperature limits CO2 uptake at low light.

The Science
Terrestrial biosphere models (TBMs) assume that the amount of carbon dioxide (CO2) taken up by plants per unit of light absorbed (quantum yield) is a global constant. This study found that in Arctic vegetation, growing at low temperature, the quantum yield is reduced, limiting the capacity for CO2 assimilation at low light levels.

The Impact
If TBMs do not account for the reduction in quantum yield at low temperature, they could overestimate the capacity of Arctic ecosystems to take up CO2 when light is limiting photosynthesis.

Summary
How TBMs represent leaf photosynthesis and its sensitivity to temperature are two critical components of understanding and predicting the response of the Arctic carbon cycle to global change. Scientists at Brookhaven National Laboratory measured the effect of temperature on the response of photosynthesis to light in six Arctic plant species and determined the quantum yield of CO2 fixation and the convexity factor, which further describes the response of photosynthesis to light. They also determined leaf absorptance to calculate quantum yield on an absorbed light basis and enable comparison with nine TBMs. The mean quantum yield at 25°C closely agreed with the mean TBM parameterization, but at lower air temperatures, measured quantum yield diverged from TBMs. At 5°C quantum yield was markedly reduced and 60% lower than TBM estimates. The convexity factor also showed a significant reduction between 25°C and 5°C. At 5°C convexity was 38% lower than the common model parameterization. These data show that TBMs are not accounting for observed reductions in quantum yield and convexity that can occur at low temperature. Ignoring these reductions could lead to a marked overestimation of CO2 assimilation at low light and low temperature.

Contacts (BER PM)
Daniel Stover
U.S. Department of Energy Office of Science, Office of Biological and Environmental Research
Climate and Environmental Sciences Division (SC-23.1)
Terrestrial Ecosystem Science
daniel.stover@science.doe.gov

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

Funding
This work was funded by the Next-Generation Ecosystem Experiments (NGEE)–Arctic project, which is supported by the Office of Biological and Environmental Research within the Department of Energy’s Office of Science.

Publications
Rogers, A., S. P. Serbin, K. S. Ely, and S. D. Wullschleger. “Terrestrial biosphere models may overestimate Arctic CO2 assimilation if they do not account for decreased quantum yield and convexity at low temperature.” New Phytologist 223(1), 167–79. [DOI: 10.1111/nph.15750]

Related Links
https://ngee-arctic.ornl.gov/

Topic Areas:

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


February 01, 2019

A New Entropy-Based Scheme Reveals Dominant Controls on Greenhouse Gas (GHG) Flux Variability in an Arctic Landscape

Soil characteristics, vegetation type, changes in vegetation during the growing season and the onset of seasonal thaw were found to be significant controls on GHG flux variability in a polygonal tundra landscape.

The Science
This study was used to develop, apply and assess a novel entropy-based scheme to characterize temporal variability in greenhouse gases (GHG), i.e., CO2 and CH4 fluxes, and identify controls of such variations in a polygonal tundra landscape near Barrow, Alaska.

The Impact
Arctic tundra environments store a vast amount of soil carbon with an acute possibility that these regions will convert from a global carbon sink to a carbon source under warmer conditions. In estimating future changes to global carbon budgets, it is therefore important to identify key controls and understand the mechanistic nature of GHG flux variations especially in carbon-rich environments. Here, we focus on a polygonal tundra environment - a dominant landscape in the Alaskan Arctic Coastal Plain - that demonstrates significant variability in GHG fluxes across space and time. Results from this study indicate that flat-centered polygons may become important sources of CO2 during warm and dry years, while high-centered polygons may become important during cold and wet years. Moreover, the identification of specific geomorphic, soil, vegetation or climatic factors that explain the most variability in GHG fluxes across three successive years (2012-14) - a dataset with significant variability in soil moisture and temperature - provides important insights on which ecosystem properties may be shifted regionally in a future climate.

Summary
Investigating the degree to which environmental factors can impact GHG fluxes in Arctic tundra environments can be especially complex and difficult to interpret because of complex spatial interactions, temporal shifts and strong interdependencies and feedbacks amongst the many primary controls. A research team from LBNL and NGEE-Arctic developed a novel entropy classification scheme that can disentangle these complex relationships and identify dominant controls on GHG flux variability within an Arctic tundra environment. Entropy analysis indicates that temporal variability in CO2 flux was governed by soil temperature variability, vegetation changes during the early and late growing season, and changes in soil moisture at higher topographic locations. Variability in CH4 flux at the site was primarily associated with vegetation changes during the growing season and temporal shifts in relationships between vegetation and environmental factors such as thaw depth. Further, results indicate that recent temperature trends and increasing length of the growing season may act to increase GHG efflux from the site. In this manner, entropy results can be used to identify mechanistic controls on GHG fluxes that may become important under changing climate.

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

(PI Contact)
Susan Hubbard
Lawrence Berkeley National Laboratory
SSHubbard@lbl.gov

Funding
This material is based upon work supported as part of the Next-Generation Ecosystem Experiments (NGEE-Arctic) at Lawrence Berkeley National Laboratory funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Award Number DE-AC02-05CH11231.

Publications
Arora, B., Wainwright, H.M., Dwivedi, D., Vaughn, L.J., Curtis, J.B., Torn, M.S., Dafflon, B. and Hubbard, S.S. “Evaluating temporal controls on greenhouse gas (GHG) fluxes in an Arctic tundra environment: An entropy-based approach.” Science of the Total Environment, 649, 284-299 (2018). [DOI: 10.1016/j.scitotenv.2018.08.251 ]

Topic Areas:

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


February 01, 2019

Volatile Monoterpene ‘Fingerprints’ of Resinous Protium Tree Species in the Amazon Rainforest

Tree resin monoterpene ‘fingerprints’ in terrestrial ecosystems.

The Science
The Amazon forest, with vast biodiversity and territorial extension, cycles more carbon and water than any other terrestrial ecosystem on the planet. However, understanding the tree species and chemical composition of this rich biodiversity and how its products can sustainably benefit humans remains a major challenge. In this study, researchers from LBNL present a new rapid field collection technique to characterize the composition of monoterpenes present in stem resins of 77 Protium individuals across 15 species in a primary rainforest ecosystem in the central Amazon rainforest. By normalizing the monoterpenes present in each tree sample by the most abundant monoterpene, they generated a database of monoterpene ‘fingerprints’ which allowed us to compare across individuals and species. From this analysis, 9 types of monoterpene ‘fingerprint’ patterns emerged, characterized by a distinct dominant monoterpene.

The Impact
The results are consistent with a previous study that found at least five divergent copies of monoterpene synthase enzymes in Protium, and suggest that each of the 9 monoterpene ‘fingerprint’ types may be determined by the presence of a distinct monoterpene synthase enzyme. A comparison of monoterpene ‘fingerprints’ between years from the same individuals showed excellent agreement, suggesting that the ‘fingerprints’ are highly sensitive to the individual/species, but show relatively low annual variability. They therefore conclude that Protium monoterpene ‘fingerprints’ show a strong dependence on species identity, but not time of collection.

This study suggests that the presented method can be used to help constrain the identity of unknown Protium species and therefore be used as a new tool in resinous tree chemotaxonomy. By characterizing the composition of monoterpene resins among Protium species in the central Amazon, the results will contribute to future Protium studies on plant-microbe and plant-insect interactions, phylogenetic relationships and evolutionary histories, atmospheric chemistry and land-surface climate interactions, and commercial uses of resins. Finally, knowledge of the distribution of specific monoterpene ‘fingerprints’ among Protium tree species will contribute to the conservation, management, and sustainable use of tropical ecosystems .

Summary
Volatile terpenoid resins represent a diverse group of plant defense chemicals involved in defense against herbivory, abiotic stress, and communication. However, their composition in tropical forests remains poorly characterized. As a part of tree identification, the ‘smell’ of damaged trunks is widely used, but is highly subjective. Here, researchers from LBNL analyzed trunk volatile monoterpene emissions from 15 species of the genus Protium in the central Amazon. By normalizing the abundances of 28 monoterpenes, 9 monoterpene ‘fingerprint’ patterns emerged, characterized by a distinct dominant monoterpene. While 4 of the ‘fingerprint’ patterns were composed of multiple species, 5 were composed of a single species. Moreover, among individuals of the same species, 6 species had a single ‘fingerprint’ pattern, while 9 species had two or more ‘fingerprint’ patterns among individuals. A comparison of ‘fingerprints’ between 2015 and 2017 from 15 individuals generally showed excellent agreement, demonstrating a strong dependence on species identity, but not time of collection. The results are consistent with a previous study that found multiple divergent copies of monoterpene synthase enzymes in Protium. They conclude that the monoterpene ‘fingerprint’ database has important implications for constraining Protium species identification and phylogenetic relationships and enhancing understanding of physiological and ecological functions of resins and their potential commercial applications.

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

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

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

Publications
Piva L, K. Jardine, B. Gimenez, V. Menezes, F. Durgante, L. Cobello, N. Higuchi, and J. Chambers. Volatile monoterpene ‘fingerprints’ of resinous Protium tree species in the Amazon Rainforest.” Phytochemistry 160, 61-70 (2019). [10.1016/j.phytochem.2019.01.014]

Related Links
Paper: Figure 1

Topic Areas:

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


January 29, 2019

Arctic Waterbodies have Consistent Spatial and Temporal Size Distributions

A high-resolution circum-Arctic assessment of pond and lake sizes reveals very consistent statistical properties over space and time.

The Science
Arctic lowlands are characterized by large numbers of small waterbodies, which are known to affect surface energy budgets and the global carbon cycle. Further, waterbody distributions are changing rapidly in the warming Arctic, and Earth System Models (ESMs) do not currently represent these dynamics. In this study, a new high-resolution (< 5 m) circum-Arctic water body data base (Permafrost Region Pond and Lake; PeRL) was used to create the first high-resolution estimation of Arctic waterbody size distributions, with surface areas ranging from 0.0001 km2 (100 m2) to 1 km2. Surprisingly consistent relationships were found between mean waterbody size across a region and both the variance and skewness of the distributions. Further, these relationships held in two regions where multi-decadal repeat photography was available.

The Impact
Characterizing the size distributions of Arctic waterbodies is a critical missing piece in assessing 21st century changes in hydrological and biogeochemical cycles and exchanges with the atmosphere. The results from this study provide important information for how these fine-resolution dynamics can be represented in ESMs, which is a goal for our NGEE-Arctic work in the Energy Exascale Earth System Model (E3SM) land model (ELMv1).

Summary
In 2017, NGEE-Arctic DOE scientists worked with a group of collaborators to create an open-source database (PeRL) of high-resolution (< 5 m) Arctic waterbody sizes (surface areas ranging from 0.0001 km2 to 1 km2; Muster et al. (2017)). The current study (Muster et al. 2019) analyzed that database over thirty study regions and found large variation in waterbody size distributions and that no single size distribution function was appropriate across all the study regions. However, close relationships between the statistical moments (mean, variance, and skewness) of the waterbody size distributions from different study regions clearly emerged: the spatial variance increased linearly with mean waterbody size (R2 = 0.97, p < 2.2e-16) and the skewness decreased hyperbolically. These relationships (1) hold across the 30 Arctic study regions covering a variety of (bio)climatic and permafrost zones, (2) hold over time in two of the regions for which multi-decadal satellite imagery is available, and (3) can be reproduced by simulating rising water levels in a high-resolution digital elevation model. The consistent spatial and temporal relationships between the statistical moments of the waterbody size distributions underscore the dominance of topographic controls in lowland permafrost areas. These results provide motivation for further analyses of the factors involved in waterbody development and spatial distribution and for how these fine-resolution dynamics can be represented in ESMs, such as the Energy Exascale Earth System Model (E3SM) land model (ELMv1).

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

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

Funding
This research was supported by the Office of Science, Office of Biological and Environmental Research of the US Department of Energy as part of the NGEE Arctic program and the Energy Exascale Earth System Model (E3SM) project.

Publications
Muster, S., W. J. Riley, K. Roth, M. Langer, F. Cresto-Aleina, C. D. Koven, S. Lange, A. Bartsch, G. Grosse, C. J. Wilson, B. M. Jones, and J. Boike. “Size Distributions of Arctic Waterbodies Reveal Consistent Relations in Their Statistical Moments in Space and Time.” Frontiers in Earth Science 7, 5 (2019). [DOI: 10.3389/feart.2019.00005]

Further reading:
Muster, S., K. Roth, M. Langer, S. Lange, F. C. Aleina, A. Bartsch, A. Morgenstern, G. Grosse, B. Jones, B. K. Sannel, Y. Sjöberg, F. Gunther, C. Andresen, A. Veremeeva, P. R. Lindgren, F. Bouchard, M. J. Lara, D. Fortier, S. Charbonneau, T. A. Virtanen, G. Hugelius, J. Palmtag, M. B. Siewer, W. J. Riley, C. D. Koven, and J. Boike. “PeRL: A Circum-Arctic Permafrost Region Pond and Lake Database, Earth System Science Data, 9, (2017). [DOI: 10.5194/essd-9-317-2017]

Topic Areas:

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


January 21, 2019

Machine-Learning-Based Measurement of Ice Wedge Polygon Properties

A rapid assessment of wet-tundra arctic landscape conditions.

The Science
Ice wedge polygons are ubiquitous features in wet-tundra Arctic landscapes. Their topographic properties control the distribution of water, vegetation and biogeochemical processes. Measuring and counting these small-scale landscape features across the Arctic is an extremely difficult proposition, but necessary to assess the state and dynamics of the landscape. A new machine learning approach can now quickly quantify these small-scale features at regional scales, and enables improved estimates of ecosystem processes across large swaths of the Arctic landscape.

The Impact
This new capability now enables scientists to quickly assess the number, configuration, and state of ice wedge polygons across large swaths of the Arctic. With this technology, scientists will be able to quickly measure how these land forms are responding to rapid arctic warming and concurrent permafrost degradation that is reshaping local to regional topography. Products from this technology are informing models to project how changes in the structure of Arctic landscapes will influence feedbacks to the climate system.

Summary
Ice wedge polygons are the surface expression of ice wedges, or vertical veins of ground ice that divide tundra landscapes into a network of polygonal units, 10-30 m across. These polygons pervade the Arctic tundra and are categorized as low centered polygons, which are surrounded by rims of soil several tens of centimeter high, or high centered polygons, surrounded by troughs on the order of a meter deep. The spatial distribution of these two types of polygon controls important landscape processes, including redistribution of windblown snow, thermal regulation of the underlying permafrost, runoff and evaporation, and surface emissions of two important but very different greenhouse gasses, carbon dioxide and methane. Therefore, mapping polygon types across the Arctic is vital for understanding the hydrologic function of landscapes, as well as potential fluxes of carbon into the atmosphere. However, directly delineating each polygon across the Arctic is impractical. Scientists at the University of Texas in collaboration with Los Alamos National Laboratory have developed a new approach that utilizes machine learning algorithms to analyze high resolution digital elevation maps from airborne remote sensing. This approach has been shown to be fast and accurate at two test sites with complex polygonal terrain, near Prudhoe Bay and Utqiagvik (formerly Barrow), Alaska. The algorithm allows scientists to quickly and accurately inventory polygonal forms across broad tundra landscapes, which will ultimately inform projections of the fate of the large stock of organic matter stored in Arctic soils.

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

(PI Contacts)
Chuck Abolt
The University of Texas at Austin
chuck.abolt@utexas.edu

Adam Atchley
Los Alamos National Laboratory
Aatchley@lanl.gov

Funding
Funding is provided by DOE Biological and Environmental Research, Terrestrial Ecosystem Science, Next Generation Ecosystem Experiments Arctic (NGEE-Arctic) and NASA Earth and Space Science Fellowship program.

Publications
Abolt, C.J., M.H. Young, A.L. Atchley, and C.J. Wilson. “Brief communication: Rapid machine-learning-based extraction and measurement of ice wedge polygons in high-resolution digital elevation models.” The Cryosphere, 13(1), 234-245 (2019). [DOI: 10.5194/tc-13-237-2019]

Related Links
Code repository:
Abolt, C.J., M.H. Young, A.L. Atchley, and C.J. Wilson. “CNN-watershed: A machine learning-based tool for delineation and measurement of ice wedge polygons in high-resolution digital elevation models.” Zenodo repository. [DOI: 10.5281/zenodo.2554542]

Topic Areas:

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


January 03, 2019

Warming Effects of Spring Rainfall Increase Methane Emissions from Thawing Permafrost

By advecting thermal energy into soil, precipitation regulates the near-term global warming potential of thawing permafrost.

The Science 
In Interior Alaska, at a thawing wetland complex located within a black-spruce permafrost forest, we measured carbon, water, and energy exchange between the land and the atmosphere over three years (2014, 2-15, 2016). The dataset is unique because we captured an average precipitation year and two years with abnormally high rainfall. Researchers from the University of Washington found that interactions between rain and deep soil temperatures controlled methane emissions. When wetland soils were warmed by spring rainfall, methane emissions increased by ~30%.

The Impact
Northern regions are expected to receive more rainfall in the future. By warming soils and increasing methane release, this rainfall could increase near-term global warming associated with permafrost thaw.

Summary
Because the world is getting warmer, permanently frozen ground around the arctic, known as permafrost, is thawing. When permafrost thaws, the ground collapses and sinks. Often a wetland forms within the collapsed area. Conversion of permanently frozen landscapes to wetlands changes the exchange of greenhouse gases between the land and atmosphere, which impacts global temperatures. Wetlands release methane into the atmosphere. Methane is a potent greenhouse gas. The ability of methane to warm the Earth is 32-times stronger than that of carbon dioxide over a period of 100 years. In this study, researchers found that methane release from the thaw wetland was greater in rainy years when rain fell in the spring. The data indicated that when it rained, water from the surrounding permafrost forest flowed downhill, entered the wetland, and rapidly altered wetland soil temperatures down to deep depths (~80 cm). Rain has roughly the same temperature as the air, and during springtime in northern regions, the air is warmer than the ground. The microbial and plant processes that generate methane increase with temperature. Therefore, wetland soils, warmed by spring rainfall, supported more methane production and release. This study identifies an important and unconsidered role of rain in governing the radiative forcing of thawing permafrost landscapes.

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

(PI Contact)
Rebecca B. Neumann
Associate Professor, Civil & Environmental Engineering, University of Washington, Seattle, WA
rbneum@uw.edu

Funding
This material is based upon work supported, in part, by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Award Number DE-SC0010338 to R.B. Neumann and the USGS Land Change Science Program. Considerable logistic support was provided by the Bonanza Creek LTER Program, which is jointly funded by NSF (DEB 1026415) and the USDA Forest Service, Pacific Northwest Research Station (PNW01-JV112619320-16).

Publications
Neumann, R.B. et al. “Warming effects of spring rainfall increase methane emissions from thawing permafrost.” Geophysical Research Letters 46(3), 1393-1401 (2019). [DOI: 10.1029/2018GL081274]

Related Links
University of Washington News Press Release
AGU Newsroom Press Release
AAAS EurekAlert!
Inside Climate news story

Topic Areas:

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


January 02, 2019

A 2017 Planetary-Scale Power Outage: Weather and Ecological Impacts of a Total Solar Eclipse

A network of eddy covariance flux towers enabled the detailed study of micrometeorological and ecosystem responses to a total solar eclipse.

The Science
Cyclic variations in solar energy at the Earth’s surface is the reason we experience changes in weather and the driver of the natural rhythms of ecosystems. Solar eclipses offer the rare chance to study how the weather and ecosystems respond to an abrupt environmental disruption of known intensity and duration—allowing for an outdoor controlled light experiment at the scale of whole ecosystems. This enables novel analyses of ecosystem processes and biosphere-atmosphere interactions. Additionally, rare natural events such as a total solar eclipse captures the attention of the public, which can be the starting point for discussions that advance the general science education.

The Impact
Knowledge of these ecosystems responses to such an abrupt perturbation of the forces driving energy, water, and carbon through those systems can inform models that scientists use to forecast weather or evaluate probable effects of future climate on ecosystems.

Summary
Mid-Missouri experienced up to 2 minutes 40 seconds of totality at around noontime during the total eclipse of 2017. We conducted the Mid-Missouri Eclipse Meteorology Experiment (MMEME) to examine land-atmosphere interactions during the eclipse. Here, research examining the eclipse responses in three contrasting ecosystems (forest, prairie, and soybeans) is described. There was variable cloudiness around at the beginning and end of the eclipse at the forest and prairie, however, skies cleared during the eclipse. Unfortunately, there were thunderstorms at the soybean site, which masked the eclipse effect and exposed the field to cold outflow. Turbulence and wind speeds decreased during the eclipse at all sites. However, there was amplified turbulent intensity at the soybean during the passage of a gust front. Evaporation and heating of the atmosphere by the land surface shut off during the eclipse as air became more stable, with the atmosphere actually supplying some heat to the surface at totality. Although the eclipse had a large effect on surface energy balances, the air temperature response was relatively muted due to the absence of topographic effects and the relatively moist land and atmosphere.

Contact (BER PM)
Daniel Stover, SC-23.1,
Terrestrial Ecosystem Science
Daniel.Stover@science.doe.gov

Jeffrey Wood, University of Missouri
woodjd@missouri.edu
and
Lianhong Gu, Oak Ridge National Laboratory
lianhong-gu@ornl.gov

Funding
National Aeronautics and Space Administration, Goddard Space Flight Center
U. S. Department of Energy Biological and Environmental Research, Terrestrial Ecosystem Science
United States Department of Agriculture-Agricultural Research Service
National Science Foundation, Missouri EPSCoR

Publication
Wood JD, EJ Sadler, NI Fox, ST Greer, L Gu, PE Guinan, AR Lupo, PS Market, SM Rochette, A Speck, and LD White. “Land-atmosphere responses to a total solar eclipse in three ecosystems with contrasting structure and physiology.” Journal of Geophysical Research: Atmospheres 124(2), 530-543 (2019). [DOI: 10.1029/2018JD029630]

Topic Areas:

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