Soil respiration represents about 50% of terrestrial CO2 emission to the atmosphere. Yet soil ecosystem processes remain poorly understood. Field and lab experiments have reported contradictory dynamics of response of soil respiration to warming. Heterotrophic microorganisms mediate the fundamental cycle of soil organic matter decomposition to soil respiration through the production of extracellular enzymes. They also adapt at the individual and community level to temperature change through different mechanisms: enzyme thermodynamic responses, plasticity of functional traits, and evolutionary responses. We propose a mathematical mechanistic model of soil matter decomposition mediated by cooperative microbes to evaluate the contribution of thermodynamic, plastic, and evolutionary processes to the response of soil respiration to warming.
Results/Conclusions
We find diffusion limitation to be key to the evolutionary stability of microbial enzyme production. Our model generally predicts that microorganisms evolve a higher investment in the production of extracellular enzymes in response to warming. The contribution of enzyme thermodynamic is significant only on a short timescale, and only if carbon substrate is limiting. Microbial plasticity can alter respiration in the same direction as the evolutionary response, thus speeding up the total soil respiration response to warming; or in a direction opposite to the evolutionary response, thus slowing down the total soil respiration response. These results show the need of integrating thermodynamic, plastic, and evolutionary responses of soil microorganisms to improve our predictions of global carbon cycle response to climate change.