Tuesday, November 14, 2006 - 1:05 PM

Microbial Determinants of Soil Carbon Response to Climate Warming.

Teri C. Balser, Univ of Wisconsin, 1525 Observatory Dr, Dept of Soil Science, Madison, WI 53706

The issue of whether soil will act as a net carbon source or sink in response to climate warming is currently a matter of intense interest. Because global soil organic carbon concentration is greater than twice that of the atmosphere, even small changes in flux can have a significant impact on atmospheric CO2. In particular, the sensitivity of recalcitrant or stabilized carbon to temperature is a critical parameter for predicting the role of soil as a feedback agent. While there is reasonable agreement that labile C will generally display a predictable pattern of response to temperature, the dynamics of older carbon largely remain a mystery. The sensitivity of recalcitrant C to rising temperature has been predicted to increase, or remain invariant. This variability is likely due to a web of interacting factors that influence carbon stability in soil (litter quality, soil mineralogy, availability of degrader organisms). As a result, temperature sensitivity of older carbon is not a simple function of enzyme response, but instead is the product of a complex suite of interactions among the varying temperature responses of competing processes such as activation energy, mineral sorption or occlusion, and acclimation of the decomposer community. If we desire a predictive understanding of the potential of soil to feedback to climate warming it will be necessary to advance our conceptual as well as quantitative models beyond the relatively simplistic assumptions embedded in current temperature sensitivity approximations. Here, I explore the biotic role in soil carbon response to global changes. I present results from experiments designed to investigate the compositional and functional response of soil microorganisms to rising temperature as well as the interacting effects of altered N deposition, precipitation, and elevated CO2.