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ORNL researchers improve soil carbon cycling models


ORNL’s new carbon cycling model could help scientists understand the role of soil microbes (MBC) in climate change by tracking extracellular enzymes (ENZ) that break down carbon-rich soil materials (SOC) into forms that microbes can respire (DOC).

A more robust model of the soil carbon cycle developed at Oak Ridge National Laboratory (ORNL) improves understanding of carbon residence time in soils and enables scientists to make more accurate climate predictions.

The model does a better job than previous models of accounting for how microbes in the soil break down carbon-rich materials and release carbon dioxide. “Soil is a big reservoir of carbon," said co-author Melanie Mayes of the Environmental Sciences Division and the Climate Change Science Institute. "Most soil carbon cycling models in use are so simplified that they ignore the fact that decomposition is actually performed by microbes.”

The ability to accurately predict future climate conditions depends on understanding how CO2 is cycled in four main reservoirs: atmosphere, oceans, soil, and biosphere. The ORNL model, Microbial-Enzyme-Mediated Decomposition, represents mechanisms of carbon decomposition in soil more accurately because it accounts for how different forms or “pools” of carbon in the soil are degraded by microbial action.

MEND simulates the chain of events that occur as plant or animal material decays and releases carbon into the soil. Enzymes released by microbes in the soil degrade the organic matter, releasing carbon molecules, which the microbes absorb as food. Eventually, the microbes release CO2.

In addition to accounting for most of the relevant processes in carbon degradation, MEND accounts for how temperature affects the ability of microbes to emit CO2. The researchers hypothesize that higher temperatures will alter the physiology of the microbes and their ability to digest carbon and release CO2 into the atmosphere, Mayes said.

The ORNL team will conduct lab-scale experiments for several months to ensure the accuracy of the model. Eventually they hope to incorporate it into the Community Land Model, a module used in the Community Earth System Model for predicting climate change.

Reference: Wang, et. al. 2013. Development of microbial-enzyme-mediated decomposition model parameters through steady-state and dynamic analyses. Ecological Applications 23:255–272.

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