Towards An Ecophysiological Understanding of Microbial Communities in Soil: Stress Responses and Climate Change.

Microbial physiological response to environmental change is often the bottleneck determining the flow and fate of elements in a disturbed ecosystem. In this study we asked how microbial response to long-term exposure to environmental stressors (such as temperature or nitrogen levels) might constrain ecosystem functioning, and whether there were changes in microbial physiologic responses to nutrient additions after long-term exposure to elevated nutrient (nitrogen, CO2) levels or climate factors (temperature, water). We used microbial lipid analysis to characterize and fingerprint the soil microbial community at the Jasper Ridge Global Change Experiment, Stanford CA. We found that after 8 years of exposure to environmental changes both general microbial community structure and physiological sensitivity to manipulated factors was altered. Nitrogen addition had the largest effect, followed by temperature. In particular, the relative abundance of mycorrhizal fungi declined under elevated N, while bacterial abundance increased. When either CO2 or temperature was elevated together with nitrogen, response to nitrogen diminished. The interactive effects of treatment were critical in predicting microbial response. In addition, communities previously exposed to elevated temperature, elevated precipitation, or nitrogen addition all had different responses to carbon, nitrogen, or phosphorus addition than soils with no prior manipulation. This work demonstrates that not only are there long-term changes in community biomass and function over time, but also that the underlying capacity of the microbial community to respond to environmental conditions changes after exposure to long-term global changes over time.