Global control of both temperature and microbes on soil carbon

While soil biotic and abiotic processes control carbon emissions and storage in terrestrial ecosystems, biotic processes are key for understanding the future fate of carbon. The faster the rate of decomposition and the lower the fraction of decomposed carbon that is converted to new biomass, the more carbon released to the atmosphere. Despite this known pathway, quantifying this control is uncertain in models. Microbial implicit models capture general environmental controls, but omit direct controls of microbial biomass and its interactions with organic matter. Microbial explicit models account for key processes, but are prone to instability and parameter identifiability issues. This leads to the question, is there an alternative approach that blends simplicity and sufficient process representation? Here, we test whether metabolic theory of ecology (MTE) can be used for predictions of soil carbon fluxes and storages. MTE captures key features of biological processes at the individual level by considering both body size and temperature effects on metabolic rates, and can be used to scale up controls to a community or ecosystem level. Motivated by the need to explain variations in soil carbon fluxes and storages with intermediate-complexity, robust models, MTE is shown to explain scaling relations between respiration rates and microbial biomass, microbial growth rates and temperature, and between the contents of soil organic carbon and microbial biomass. This presents an opportunity to compare scaling relations in observational data and models, and potential to provide insight into global scale parameterising of microbial explicit models. This may help to reduce uncertainties in the future carbon feedback in the soil.