Citation. Chung, H. 2005. Interactive effects of global change on soil microbial community composition and function. Ph.D. Thesis, University of Michigan.

Abstract. Anthropogenic activity has altered biogeochemical cycles and reduced plant species richness on a global basis. Atmospheric CO 2 and O 3 enrichment, atmospheric N deposition, and plant species loss alter plant production and litter biochemistry, which could modify heterotrophic soil microbial activity. The objective of my dissertation research was to determine the interactive effects of these global change components on microbial community composition and metabolism. To achieve this goal, I studied changes in composition and function of soil microbial communities in two distinct experiments
in which levels of atmospheric CO 2 , O 3 , N deposition, and plant species richness were manipulated to simulate aforementioned global change. I analyzed the combined impacts of CO 2 and O 3 enrichment on fungal community composition and function in an experiment in which northern hardwood trees were grown under elevated levels of CO 2 and O 3 . Elevated CO 2 enhanced fungal metabolism through greater plant litter input as evidenced by higher cellulolytic and chitinolytic activity, and elevated O 3 dampened this effect via reduced substrate input; however, the interactive effects of CO 2 and O 3 were not statistically significant. Repressed fungal metabolism under elevated O 3 was accompanied by a change in fungal community composition. My results suggest that elevated CO 2 will stimulate fungal metabolism and hasten belowground C cycling, and that repressed fungal activity and changes in fungal community
composition under elevated O 3 will lead to slower soil C cycling.