A Comparison of Arrhenius and Macromolecular Rate Theory for Predicting Temperature Responses of Soil CO2 Production

Abstract:

Soil microbes catalyze many key ecosystem functions, including soil respiration, and are thus important for understanding global carbon cycles and other biogeochemical cycles. One important component in predicting rates of respiration is determining how microbial communities respond to temperature. A range of models have been developed for determining temperature sensitivity of soil biological activities, most of which are based on the Arrhenius equation. This equation predicts an exponential increase in rate with temperature, despite field and laboratory results suggesting a temperature optimum below the denaturation point. Recently, Schipper et al. (2014) developed a novel theory, Macromolecular Rate Theory (MMRT), which explains this trend due to heat capacity (C_P) changes associated with enzymes. We applied MMRT to respiration data collected using a reciprocal transplant design with soils from three different sites across the U.S. Great Plains to isolate the effects of microbial community type from edaphic factors. We found that MMRT provided a better fit to the data than Arrhenius in 8 out of the 9 soil x inocula combinations. Our analysis revealed that the microbial communities have distinct C_P values largely independent of soil type. These results have significant implications for fundamental understanding of microbial enzyme dynamics in soils as well as for ecosystem and global carbon modeling.