Interactive Effects of Resources and Stress on Soil Microbial Communities and Processes.

The combination of physical heterogeneity, environmental variability, and a diversity of chemical substrates make soil the most complex environment for life on the planet. Moreover, strong gradients of resource availability and stress exist through soil profiles.  This project evaluates the mechanisms regulating microbial dynamics through drying/wetting cycles in California grassland, testing the hypothesis: “Stress and C availability are multiplicative in their effects on microbial community composition and function”.  The availability of C may mediate the intensity of stress experienced by microbes as microbes use C for their growth, and to produce osmotic agents and extracellular polysaccharide layers that retain moisture. Environmental changes may alter resource supply: drought reduces substrate diffusion while rewetting releases soil organic matter. Recognizing that microbes use many different monomers and polymers in soil, we also postulate that the quantity and quality of C will dictate substrate partitioning with varying environmental conditions. This project evaluates how resource availability and drying/wetting cycles regulate microbial communities, populations, and functional groups through the soil profile. Resource and stress regimes are experimentally-manipulated and microbial responses evaluated. Overall, this project is delivering understanding of the interactive effects of resource and stress on soil microbes which is key to understanding all microbial life in soil.