BER Research Highlights

Search Date: December 13, 2017

6 Records match the search term(s):


November 05, 2014

Multiscale Model Unifies Simulation of Surface and Groundwater Flow

Modeling hydrological processes in ecosystems containing both surface water and groundwater is crucial for understanding fluid flow in general, and, more specifically, for understanding the cycling of organic and inorganic elements and the availability of nutrients to microbes and plants. Such understanding could lead to approaches to better control carbon and water cycles, mitigate contamination, and enhance nutrient availability for bioenergy crops. However, a long-standing challenge has been that models use separate sets of equations to describe fluid flow in surface water and groundwater, thus requiring complex approaches to couple equations. Now, scientists from the University of Central Florida and Pacific Northwest National Laboratory have developed a unified multiscale model that uses a single set of equations to simultaneously simulate fluid flow in an ecosystem containing both surface water and groundwater. Simulations were performed using the Cascade supercomputer at the Environmental Molecular Sciences Laboratory, one of the Department of Energy’s scientific user facilities. The team applied the modeling approach to the Disney Wilderness Preserve in Kissimmee, Florida, where active field monitoring and measurements are ongoing to understand hydrological and biogeochemical processes. The simulation results demonstrated that the Disney Wilderness Preserve is subject to frequent changes in soil saturation, geometry and volume of surface waterbodies, and groundwater and surface water exchange. The unified multiscale model is expected to lead to a better understanding of fluid flow in active groundwater and surface water interaction zones, such as wetlands, which play important roles in global cycling of carbon and nitrogen, degradation of metals and organic contaminants, and production and mitigation of greenhouse gases.

References: Yang, X., C. Liu, Y. Fang, R. Hinkle, H.-Y. Li, V. Bailey, and B. Bond-Lamberty. 2015. “Simulations of Ecosystem Hydrological Processes Using a Unified Multi-Scale Model,” Ecological Modelling 296,93–101. DOI: 10.1016/j.ecolmodel.2014.10.032. (Reference link)
Further information

Contact: Paul E. Bayer, SC-23.1, (301) 903-5324
Topic Areas:

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


October 13, 2014

Contemporary Terrestrial Biosphere May Be More CO2 Limited than Previously Thought

In plants with C3 photosynthetic pathways, CO2 concentrations drop considerably along leaf mesophyll diffusion pathways from sub-stomatal cavities to chloroplasts where CO2 assimilation occurs. Global carbon cycle models have not explicitly represented this internal drawdown, overestimating CO2 available for carboxylation and underestimating photosynthetic responsiveness to atmospheric CO2. Researchers at Oak Ridge National Laboratory sought to determine how mesophyll diffusion affects the global land CO2 fertilization effect estimated by global carbon models. The team found that current carbon cycle models underestimate by 16% the long-term responsiveness of global terrestrial productivity to CO2 fertilization. This underestimation of CO2 fertilization is caused by an inherent model structural deficiency related to a lack of explicit representation of CO2 diffusion inside leaves, which results in an overestimation of CO2 available at the carboxylation site. The magnitude of CO2 fertilization underestimation matches the long-term positive growth bias in the historical atmospheric CO2 predicted by Earth system models. This finding implies that the contemporary terrestrial biosphere is more CO2 limited than previously thought and will lead to improved understanding and modeling of carbon-climate feedbacks.

Reference: Sun, Y., L. Gu, R. E. Dickinson, R. J. Norby, S. G. Pallardy, and F. M. Hoffman. 2014. “Impact of Mesophyll Diffusion on Estimated Global Land CO2 Fertilization,” Proceedings of the National Academy of Sciences (USA) 111(44), 15,774-779. DOI: 10.1073/pnas.1418075111. (Reference link)

Contact: Daniel Stover, SC-23.1, (301) 903-0289, Mike Kuperberg, SC-23.1, (301) 903-3281
Topic Areas:

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


October 13, 2014

Elevated CO2 Suppresses Dominant Plant Species in a Mixed-Grass Prairie

Climate controls vegetation distribution across the globe, with some vegetation types being more vulnerable to climate change and others more resistant. Because resistance and resilience can influence ecosystem stability and determine how communities and ecosystems respond to climate change, it is important to evaluate the potential for resistance in future ecosystem function. In a mixed-grass prairie in the northern Great Plains, researchers utilized a large field experiment to test the effects of elevated CO2, warming, and summer irrigation on plant community structure and productivity. This study sought to understand changes to both stability in plant community composition and biomass production. The researchers found that the independent effects of CO2 and warming on community composition and productivity depend on interannual variation in precipitation and that the effects of elevated CO2 are not limited to water saving because they differ from those of irrigation. They also show that production in this mixed-grass prairie ecosystem is not only relatively resistant to interannual variation in precipitation, but also rendered more stable under elevated CO2 conditions. This increase in production stability is the result of altered community dominance patterns: Community evenness increases as dominant species decrease in biomass under elevated CO2. In many grasslands that serve as rangelands, the economic value of the ecosystem is largely dependent on plant community composition and the relative abundance of key forage species. These results have implications for how native grasslands are managed in the face of changing climate.

Reference: Zelikova, T. J., D. M. Blumenthal, D. G. Williams, L. Souza, D. R. LeCain, J. Morgan, and E. Pendall. 2014. “Long-Term Exposure to Elevated CO2 Enhances Plant Community Stability by Suppressing Dominant Plant Species in a Mixed-Grass Prairie,” Proceedings of the National Academy of Sciences (USA) 111(43), 15,456-461. DOI: 10.1073/pnas.1414659111. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

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


May 02, 2014

Faster Decomposition Under Increased Atmospheric CO2 Limits Soil Carbon Storage

Carbon dioxide (CO2) is released to the atmosphere when humans burn oil, coal, and gasoline, and it is the major cause of global warming. Soils can store carbon, helping to counteract rising CO2. Carbon accumulates in soil through many years of plant photosynthesis, but also is lost from soil as microscopic organisms, mostly bacteria and fungi, decompose soil carbon, converting it back to CO2 and releasing it to the atmosphere. The balance of these two processes and the future of the soil carbon sink are uncertain. How much will soil organic carbon persist, and how much will soil microorganisms convert back to CO2, returning it to the atmosphere? This study compared data gathered from experiments around the world with models of the soil carbon cycle to test how carbon release from soil by microorganisms responds to rising CO2. The main finding was surprising: increased plant growth caused by rising atmospheric CO2 was associated with higher rates of CO2 release from soil. On balance, the findings suggest that if rising CO2 enhances carbon storage in soil at all, the effect will be small. These results indicate that soil carbon may not be as stable as previously thought, and that soil microorganisms exert more direct control on long-term carbon accumulation than currently represented in global models.

Reference: Van Groenign, K. J., X. Qi, C. W. Osenberg, Y. Luo, and B. A. 2014. “Faster Decomposition Under Increased Atmospheric CO2 Limits Soil Carbon Storage,” Science 344(6183), 508-509. DOI:10.1126/science.1249534. (Reference link)

Contact: Renu Joseph, SC-23.1, (301) 903-9237, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

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


February 01, 2014

Isoprene Fluxes from an Oak-Dominated Temperate Forest

Isoprene is a biogenic volatile organic compound. Its oxidation in the atmosphere affects both the production of tropospheric ozone and secondary aerosol formation. Isoprene production by plants, therefore, has implications for the control of regional air quality and global climate change. Scientists at Oak Ridge National Laboratory recently conducted a study to understand these isoprene emissions and to test predictive models at multiple scales. The study took place at the Missouri Ozark AmeriFlux (MOFLUX) site in central Missouri, an oak-hickory dominated forest. Ecosystem fluxes of isoprene emissions were measured during the 2011 growing season. The isoprene flux measurements were used to test understanding of the controls on isoprene emission from hourly to seasonal timescales with a state-of-the-art emission model, MEGAN (Model of Emissions of Gases and Aerosols from Nature). Isoprene emission rates observed during the drought of 2011 reached 53.3 mg m-2 h-1 (217 nmol m-2 s-1), the highest ever recorded for any ecosystem in the world. The MEGAN model correctly predicted isoprene emission rates before drought, but its performance deteriorated as the drought progressed (in response to water stress). Overall, MEGAN’s performance was robust and could explain 90% of the observed variance in the measured fluxes, but the response of isoprene emission to drought stress is a major source of uncertainty. Since isoprene is chemically reactive in the atmosphere, it is critically important to understand these emissions as well as to incorporate this process into atmosphere-biosphere models.

Reference: Potosnak, M. J., L. LeStourgeon, S. G. Pallardy, K. P. Hosman, L. H. Gu, T. Karl, C. Gerone, and A. B. Guenther. 2014. “Observed and Modeled Ecosystem Isoprene Fluxes from an Oak-Dominated Temperate Forest and the Influence of Drought Stress,” Atmospheric Environment 84, 314–22. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

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


January 08, 2014

Symbiotic Fungi Inhabiting Plant Roots Have Major Impact on Atmospheric Carbon

Of central concern to climate change science is the potential for natural feedbacks to the warming currently under way as a result of anthropogenic CO2 emissions. Soil is the largest reservoir of carbon in the terrestrial biosphere, containing more than that already found in the atmosphere and biomass combined. If soils were to lose even a small fraction of their carbon, climate could change rapidly with important repercussions for U.S. policy on topics as disparate as food security and coastal inundation. To date, it is has been difficult to identify the factors controlling gains of soil carbon on local to global scales. In recent study, researchers show that mycorrhizal fungi—symbiotic fungi on plant roots—control the quantity of carbon in today’s soils. Using global datasets, they found that the soil in ecosystems dominated by ecto- and ericoid mycorrhizal fungi contains ~70% more carbon than those dominated by arbuscular mycorrhizal fungi. In their analysis, the effect of mycorrhizal type on soil carbon pools was of far larger consequence than the effects of an ecosystem’s productivity, its climate (i.e., temperature and precipitation) or the physical properties of its soil (e.g., clay content). While the mechanism accounting for the difference in soil carbon storage is still debated, it appears that competition for nitrogen in the soil provides the best answer. Ecto- and ericoid mycorrhizal fungi produce many different types of enzymes that they release into the soil in an effort to unlock the nitrogen bound to carbon pools in soil. These fungi also are very effective competitors for nitrogen, making it very scarce to other decomposers in the soil, reducing their biomass and hence the rate of decomposition. By contrast, arbuscular mycorrhizal fungi lack many of these enzyme systems and decomposition rates are rapid. Importantly, this research links the traits of mycorrhizal fungi to carbon storage at the global scale—from tropical forests to the far northern reaches of the boreal forest—suggesting that decomposer competition for nutrients exerts fundamental control over the terrestrial carbon cycle. Whether climate change alters the distribution of these different fungal species remains to be seen, but increases in the abundance or geographical spread of arbuscular mycorrhizal may portend a significant, biologically controlled positive feedback to the climate system.

Reference: Averill, C., B. L. Turner, and A. C. Finzi. 2014. “Mycorrhiza-Mediated Competition Between Plants and Decomposers Drives Soil Carbon Storage,” Nature 505, 543-45. DOI:10.1038/nature12901. (Reference link)

Contact: Mike Kuperberg, SC-23.1, (301) 903-3281, Daniel Stover, SC-23.1, (301) 903-0289
Topic Areas:

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