Thermal Adaptation of Enzyme-Mediated Processes Reduces Simulated Soil CO2 Fluxes Upon Soil Warming

Understanding factors influencing carbon effluxes from soils to the atmosphere is important in a world experiencing climatic change. Two important uncertainties related to soil organic carbon (SOC) stock responses to a changing climate are (a) whether soil microbial communities acclimate or adapt to changes in soil temperature and (b) how to represent this process in SOC models. To further explore these issues, we included thermal adaptation of enzyme-mediated processes in a mechanistic SOC model (ReSOM) using the macromolecular rate theory. Thermal adaptation is defined here to encompass all potential responses of soil microbes and microbial communities following a change in temperature. To assess the effects of thermal adaptation of enzyme-mediated processes on simulated SOC losses, ReSOM was applied to data collected from a 13-year soil warming experiment. Results show that a model omitting thermal adaptation of enzyme-mediated processes substantially overestimates observed CO₂ effluxes during the initial years of soil warming. The bias against observed CO₂ effluxes was lower for models including thermal adaptation of enzyme-mediated processes. In addition, for a simulated linear 3°C soil warming over 100 years, models including thermal adaptation of enzyme-mediated processes simulated SOC losses of a factor of three smaller than models omitting this process. As thermal adaptation of microbial community characteristics is generally not included in models simulating feedback between the soil, biosphere and atmosphere, we encourage future studies to assess the potential impact that microbial adaptation has on soil carbon – climate feedback representations in models.