Integrating microbial physiology and physio-chemical principles in soils with the MIcrobial-MIneral Carbon Stabilization (MIMICS) model

A growing body of literature documents the press- ing need to develop soil biogeochemistry models that more accurately reflect contemporary understanding of soil pro- cesses and better capture soil carbon (C) responses to en- vironmental perturbations. Models that explicitly represent microbial activity offer inroads to improve representations of soil biogeochemical processes, but have yet to consider relationships between litter quality, functional differences in microbial physiology, and the physical protection of micro- bial byproducts in forming stable soil organic matter (SOM). To address these limitations, we introduce the MIcrobial- MIneral Carbon Stabilization (MIMICS) model, and evalu- ate it by comparing site-level soil C projections with obser- vations from a long-term litter decomposition study and soil warming experiment. In MIMICS, the turnover of litter and SOM pools is governed by temperature-sensitive Michaelis- Menten kinetics and the activity of two physiologically dis- tinct microbial functional types. The production of micro- bial residues through microbial turnover provides inputs to SOM pools that are considered physically or chemically pro- tected. Soil clay content determines the physical protection of SOM in different soil environments. MIMICS adequately simulates the mean rate of leaf litter decomposition observed at temperate and boreal forest sites, and captures observed effects of litter quality on decomposition rates. Moreover, MIMICS better captures the response of SOM pools to exper- imental warming, with rapid SOM losses but declining tem- perature sensitivity to long-term warming, compared with a more conventional model structure. MIMICS incorporates current microbial theory to explore the mechanisms by which litter C is converted to stable SOM, and to improve predic- tions of soil C responses to environmental change.