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Microbial community structure and ecosystem function in a changing world

Cregger, M.A. 2012. Ph.D. dissertation. University of Tennessee, Knoxville


Understanding the effects climate change will have on the structure and function of global ecosystems is a pressing ecological and social issue. Global change driven changes in atmospheric warming and precipitation regimes have begun to alter the distribution of plants and animals in, as well as the function of, ecosystems. Using two large-scale climate change manipulations, I assessed the effect of changing precipitation and temperature regimes on soil microbial community structure and function. Soil microbial communities regulate decomposition and nutrient cycling rates in ecosystems, thus understanding their response to climatic changes will enable scientists to better predict carbon feedbacks to the atmosphere as well as functional shifts within ecosystems. My first two chapters took advantage of a large-scale precipitation manipulation in a semi-arid woodland. My first chapter aimed to understand how changing precipitation amounts altered the structure and abundance of soil bacteria and fungi; while my second chapter measured how changing precipitation altered soil nitrogen cycling. Overall, I found that soil microbial community composition and function were responsive to changes in precipitation, but these responses were contingent upon seasonal variability in precipitation and the aboveground plant community. My final experiment examined how changing temperature altered soil microbial community structure and function in two temperate forests. Using a large scale warming experiment at two locations, I examined how changes in temperature altered microbial composition, abundance, potential enzyme activity, and decomposition. I found that the effects of warming were contingent upon location; microbial community composition responded to alterations in soil temperature and soil moisture at the warmer site, but not at the cooler site. Unexpectedly, the change in microbial community composition did not result in changes in the rate of decomposition. I conclude that the soil is relatively buffered from atmospheric warming thus changes in microbial community structure and function may take longer than a few years to develop. Taken together, my research demonstrates that understanding the effects of climate change on microbial community structure and function is complex and contingent upon the background abiotic and biotic variability within an ecosystem.