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A central goal of global change biology is to predict the impact of environmental change on ecosystem processes. Currently, most global change models treat the local microbial community as a single, homogenously functioning entity, thereby assuming that the specific microbial composition is functionally irrelevant. However, microorganisms perform key transformations in ecosystems, and recent research demonstrates that microbial communities vary greatly across space and in response to environmental change. Therefore, parameters describing microbial communities may be key for improving predictions of how future global changes will impact ecosystem processes. For this reason, my dissertation research examined the effect of environmental changes on resident communities and determined how potential shifts in microbial community composition will impact litter decomposition rates. To accomplish this, I gathered litter samples from a chaparral ecosystem undergoing global change manipulations (elevated nitrogen availability or reduced precipitation), and characterized the microbial community using 454 high-throughput sequencing (Chapter 1). While microbial communities are much more variable through time, this research showed that microbial composition will likely shift in response to environmental change. I also examined the role of microbial community composition for a key ecosystem process, litter decomposition, and how that role changes under environmental perturbations. By isolating microbial taxa from the same ecosystem discussed above, I constructed artificial microbial communities with varying composition. I then conducted a laboratory experiment in which I subjected the communities to different global change manipulations and monitored decomposition rates and community composition (Chapter 2). Microbial composition had a main effect on leaf litter decomposition and also interacted with the environmental treatment, suggesting that future shifts in microbial communities will influence the magnitude in which environmental change affects ecosystem processes. Lastly, I investigated the functional and response traits of individual microbial taxa to better predict how microbial communities might respond to global change perturbations, and found that many functional traits displayed a phylogenetic pattern, but a taxaâs response to increased temperature did not (Chapter 3). Ultimately, this set of studies further justifies the need to incorporate microbial communities into models and begins to identify which parameters might be most relevant.