Soil microbes are key drivers of the global carbon cycle, through their role in the decomposition process and heterotrophic respiration. Yet how these microbe-driven processes change in a warming climate is poorly understood. In particular, even though we expect microbial populations to evolve rapidly in response to selection, we know little about how selection regimes on microorganisms change with temperature, how microbial populations respond, how their response feeds back on the carbon cycle, and ultimately on climate. We take a trait-based modelling approach to address these questions, assuming that a key decomposition trait of microbes – the rate at which they produce extracellular enzymes – is genetically variable. We develop an eco-evolutionary model of the response of the enzyme-production trait and use the model to investigate (i) the evolutionary response of the enzyme-production trait to warming, (ii) how this evolutionary response feeds back on soil carbon stocks, and (iii) how these effects may vary between specific biomes for which data needed to calibrate the model are available.
Results/Conclusions
The model generally predicts that microorganisms evolve a higher investment in the production of extracellular enzymes in response to warming. As a consequence, microbial adaptive evolution is predicted to accelerate decomposition and therefore to increase soil carbon loss predicted by purely ecological models. This effect is predicted to be more pronounced in ecosystems where the microbial community is dominated by relatively short-lived organisms that produce efficient enzymes at a low rate. Using existing measurements of enzyme activity across a thermal range, we obtain quantitative predictions for five specific biomes, with strongest evolutionary effects for a cold biome at high latitude. Our results highlight the pressing need to include soil eco-evolutionary feedbacks to carbon cycling in global climate models.