A major goal of microbial ecology is to understand the biotic and abiotic factors that help maintain biodiversity and ecosystem functioning in different habitats.  This goal is particularly challenging in soils, which are some of the most diverse microbial systems on Earth.  It has been hypothesized that soil moisture is a “master variable” that may help explain patterns of soil microbial diversity.  On one hand, soil moisture may influence diversity by altering the connectivity and habitat heterogeneity of the soil matrix.  On the other hands, soil moisture may influence diversity through its effects on microbial stress physiology.  In this talk, we present results from a simulation model and experiments that were designed to assess the relative importance of moisture-mediated effects of habitat heterogeneity and physiological stress on soil microbial diversity.   Results/Conclusions

Using a spatially explicit multiscale modeling approach, we have simulated the responses of single microbial species with different life history traits to moisture regimes in soils with contrasting physical properties.  This approach provided us with the direct effect of the environment on microbial dynamics and ecosystem function (i.e., respiration).  We then performed additional simulations under the same range of conditions with varying levels of microbial species diversity.  This approach let us examine how soil composition and water supply regime interact to permit species coexistence.  Laboratory microcosm experiments were conducted with a phylogenetically and physiologically diverse collection of soil microbes.  Estimates of population growth rates, respiration rates, and survivorship varied among species.  This information was used to parameterize our simulation model, but also allowed us to test predictions about how different groups of microorganisms respond to moisture variability.  Together, the integrated theoretical and empirical approach allows us to discern the importance of habitat heterogeneity and physiological stress on the maintenance of microbial diversity.