Study models soil-pore features that hold or release carbon.
Researchers recently studied how moisture influences soil heterotrophic respiration, the process by which microbes convert dead organic carbon in soil to carbon dioxide. Their cost-effective modeling strategy is the first to investigate the effect of moisture on these climate-critical respiration rates at the hard-to-simulate pore scale. The study also finds that simulations must acknowledge the diversity of soil-pore spaces, moving beyond the modeling assumption that they are homogeneous.
Globally, soils store enormous quantities of organic carbon, some of which is consumed by microbes and exhaled as carbon dioxide. In this way, soils annually produce a major natural carbon dioxide flux into the atmosphere, in an amount roughly six times larger than human emissions of the same greenhouse gas. Understanding what influences this flux has enormous implications for understanding climate change, the carbon cycle, and setting emissions targets.
Moisture conditions in soil affect the respiration rate of heterotrophic microbes. Soils are made of sand, silt, clays, and organic matter. Within all this material, miniature "porospheres" interlock to create microbial habitats made of water and gases. Modeling heterotrophic respiration at this "pore scale" is difficult because of two factors: (1) the computational challenges of modeling fluids at this scale and (2) the microscale differences within soil. In every soil, distribution of organic carbon is highly localized and dependent on physical protection, chemical recalcitrance, pore connectivity, nonuniform microbial colonies, and local moisture content.
This study, led by researchers at Pacific Northwest National Laboratory, is the first to conduct a pore-scale investigation of how moisture-driven respiration rates are affected by soil pore structure heterogeneity, soil organic carbon bioavailability, moisture content distribution, and substrate transport. The work provides insight into the physical processes that control how soil respiration responds to changes in moisture conditions. The paper's numerical analyses represent a cost-effective approach for investigating carbon mineralization in soils.
The simulations in this study generally confirmed that the soil respiration rate is a function of moisture content, that such rates increase as moisture (and therefore substrate availability) increases, and that soil respiration decreases after some optimum because of oxygen limitation. The model's results, also replicated by field research, show that respiration rates go up with higher soil porosity, and that compacted soils those with less porosity because they are unplowed and undisturbed - reduce the rate at which carbon dioxide escapes into the atmosphere. The study also warned of a danger to assuming uniform porosity in modeled soils; instead, the researchers found, the structural heterogeneity (diversity) of soils should be modeled as it exists in nature.
Further research is needed to determine how coupled aerobic and anaerobic processes would speed up or slow down the amount of organic carbon sequestered in soil.
Daniel Stover and Jared DeForest
Daniel.Stover@science.doe.gov (301-903-0289) and Jared.DeForest@science.doe.gov (301-903-1678)
Chongxuan.email@example.com; firstname.lastname@example.org (509-371-6350)
This research was supported by the U.S. Department of Energy (DOE) Office of Biological and Environmental Research through the Terrestrial Ecosystem Science (TES) program. Part of the research was performed at the Environmental Molecular Sciences Laboratory, a DOE user facility located at Pacific Northwest National Laboratory.
Z. Yan, et al., "Pore-scale investigation on the response of heterotrophic respiration to moisture conditions in heterogeneous soils." Biogeochemistry 131(1), 121-134 (2106). DOI: 10.1007/s10533-016-0270-0. (Reference link)
SC-23.1 Climate and Environmental Sciences Division, BER
BER supports basic research and scientific user facilities to advance DOE missions in energy and environment. More about BER
Aug 24, 2019
New Approach for Studying How Microbes Influence Their Environment
A diverse group of scientists suggests a common framework and targeting of known microbial processes [more...]
Aug 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. [more...]
Aug 05, 2019
Amazon Forest Response to CO2 Fertilization Dependent on Plant Phosphorus Acquisition
AmazonFACE Model Intercomparison. The Science Plant growth is dependent on the availabi [more...]
Jul 29, 2019
A Slippery Slope: Soil Carbon Destabilization
Carbon gain or loss depends on the balance between competing biological, chemical, and physical reac [more...]
Jul 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- [more...]
List all highlights (possible long download time)