PARENT SESSION
Organized Oral Session 26: From microbes to ecosystems: How do we really make the connections?
Organizer(s): J Schimel and S Frey
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 510a, Level 5, Palais des congrès de Montréal

The CENTURY of microbes: Incorporating microbes into a soil organic matter model.

Lawrence, Corey^*,1, Neff, Jason¹, Schimel, Joshua², Miller, Amy³, ¹ Department of Geological Sciences, Boulder, Colorado, U.S.A.² Department of Ecology, Evolution and Marine Biology, Santa Barbara, California, U.S.A.³ National Park Service, Anchorage, Alaska, U.S.A.

ABSTRACT- Models of terrestrial biogeochemistry have traditionally included little detail about microorganisms or mechanisms related to microbial decomposition. Rather, in most models microbial processes are represented implicitly with physical controls such as temperature and moisture that modify experimentally determined optimum rates of decomposition. In this study, we ask whether explicit representation of microorganisms and/or microbial mechanisms improves estimates of CO₂ flux. Biogeochemical models typically represent decomposition of organic matter as zero or first order kinetic equations that are modified by soil biophysical properties. In reality, decomposition is catalyzed by a suite of microbial enzymes that may vary across microbial communities and sites. To account for this complexity, we developed a model that included microbial controlled enzyme pools and explicitly represented microbial controls on decomposition. In this model, rates of decomposition are directly mediated by enzyme pool size, turnover time, and sensitivity to moisture and temperature. We tested our model against a laboratory drying-rewetting experiment where Mediterranean type soils were wetted at 2 and 4 week intervals. We compared the results of the modified model with those from first order model of SOM. The addition of microbe and enzyme controls on decomposition rates significantly improved the models ability to match the time course of soil CO₂ efflux in the laboratory experiment and particularly the short term (<24hr) release of C following wetting. These results indicate that the calculation of net carbon flux in traditional biogeochemical models may miss detail which could be captured by models that represent microbial decomposition processes more explicitly.

Key words: microbes, enzymes, carbon, models