Scaling up microbial community responses to climate change

Earth system models are essential for predicting the future effects of climate change on the biosphere. Recent efforts have begun to include microbial properties in these models, but it remains unclear how to represent complex microbial communities at the global scale. Trait-based models are promising tools for aggregating microbial traits and responses. These small-scale models can be used to extract the statistical properties of complex communities for use in parameterizing larger-scale models. This approach could account for the impact of microbial complexity without directly representing diverse microbial communities at the global scale. Here we use a trait-based and spatially-explicit model to extract microbial responses to changes in temperature and moisture. The model represents moisture through effects on diffusion rates and enzyme kinetic constants. Temperature effects on microbial processes are represented through Arrhenius-type kinetics. We asked how changes in temperature and moisture interact with microbial traits to determine rates of decomposition. Our approach allowed for tradeoffs between enzymatic traits, drought tolerance, and thermal tolerance. Moisture reduction impacted the distribution of enzymatic traits in the simulated microbial community and reduced predicted decomposition rates. Temperature increase also shifted the distribution of enzymatic traits due to tradeoffs with substrate use efficiency. Together, these shifts dampened the temperature sensitivity of overall decomposition. Overall, our results suggest that small-scale models of microbial traits and interactions are promising tools for parameterizing temperature and moisture sensitivities in ecosystem and global models.