Microbial eco-evolutionary dynamics of decomposition and dormancy

Soil microorganisms regulate a major component of the terrestrial carbon cycle, yet predictions of soil carbon stocks and fluxes often neglect microbial life-history adaptation. To fill this gap, we develop a spatially and stage-structured eco-evolutionary model in which active and dormant microbes move between favorable microsites and an unfavorable bulk soil matrix; decompose organic carbon through costly exoenzyme production; and evolve both exoenzyme investment and entry into dormancy. The model shows that dormancy expands the ecological conditions under which microbial populations persist and has a non-monotonic effect on soil carbon stocks. Adaptive dormancy is shaped by opposing selection in microsites, where inactivity carries an opportunity cost, and in the matrix, where dormancy protects cells from mortality. When dormancy and exoenzyme production jointly evolve, the traits may increase together under high microbial mobility, but often evolve in opposite directions because both carry survival benefits in the matrix. These eco-evolutionary feedbacks can either amplify or attenuate soil carbon fluxes to the atmosphere, depending on soil structure, microbial movement, and dormancy costs. Our results suggest that incorporating microbial life-history evolution into soil carbon models is essential for predicting soil carbon feedbacks to climate.