Microbial growth is the key to predict biogeochemistry from ecology

It is well known that microbes run soil biogeochemistry. Despite a century of progress in microbial ecology, translating microbial ecology into consequences for the atmosphere-soil carbon balance remains elusive. I posit that the solution to this problem is to assume the vantage point of the organisms whose functions we seek to understand: what is it that microbes want to achieve? Organisms ‘want to’ grow. Achieving growth defines both evolutionary fitness and ecological success. Thus, the complex coordination of a physiology matched to the environment, targeting resources that can be tapped, and outmanouvering any other organism that could get in your way, altogether defining growth presents a metric that integrates an organism’s response traits, and thus can be used to predict its performance and response to change. Simultanously, rates of growth capture the metabolism which is the engine that runs global biogeochemistry. As such, we can quantify an organism’s effect trait that can be used to estimate ecosystem fluxes of elements.

Using temperature as a case study, I will show how sensitive estimates of growth can be used to generate microbial community trait distributions that can be used to capture how microbial processes depend on temperature, and will respond to change (response traits). I will show how microbial thermal trait distributions vary along both latitudinal and altitudinal gradients in environmental temperatures, and how they respond to warming in field experiments, and how they respond to reciprocal transplant experiments from warm to cool sites, and vice versa. I will also show how microbial thermal trait distributions dynamically change over the course of a heatwave, revealing that it is the rate of community turnover (defined by several interacting environmental drivers including temperature and moisture) that determines its rate of change.

Finally, I will show how thermal traits determined with sensitive estimates of microbial growth can be accurately modelled with simple mathematical functions which enable integration into representations of the soil carbon cycle in Earth system models. I will demonstrate how this integration of microbial ecology via estimates of growth will allow us to capture long-term ecosystem changes in carbon stocks in warming soils, and can be upscaled to predict the biosphere’s feedback to ongoing climate change.