The Environmental Microbiome In A Changing World: Microbial Processes And Biogeochemistry

Climate change can alter ecosystem processes and organismal phenology through both long-term, gradual changes and alteration of disturbance regimes. Because microbes mediate decomposition, and therefore the initial stages of nutrient cycling, soil biogeochemical responses to climate change will be driven by microbial responses to changes in temperature, precipitation, and pulsed climatic events. Improving projections of soil ecological and biogeochemical responses to climate change effects therefore requires greater knowledge of microbial contributions to decomposition. This dissertation examines soil microbial and biogeochemical responses to the long-term and punctuated effects of climate change, as well as improvement to decomposition models following addition of microbial parameters. First, through a climate change mesocosm experiment on two soils, I determined that biogeochemical losses due to warming and snow reduction vary across soil types. Additionally, the length of time with soil microbial activity during plant dormancy increased under warming, and in some cases decreased following snow reduction. Asynchrony length was positively related to carbon and nitrogen loss. Next, I examined soil enzyme activity, carbon and nitrogen biodegradability, and fungal abundance in response to ice storms, an extreme event projected to occur more frequently under climate change in the northeastern United States. Enzyme activity response to ice storm treatments varied by both target nutrient and, for nitrogen, soil horizon. Soil horizons often experienced opposite response of enzyme activity to ice storm treatments, and increasing ice storm frequency also altered the direction of the microbial response. Mid-levels of ice storm treatment additionally increased fungal hyphal abundance. Finally, I added explicit microbial parameters to a global decomposition model that previously incorporated climate and litter quality. The best mass loss model simply added microbial flows between litter quality pools, and addition of a microbial biomass and products pool also improved model performance compared to the traditional implicit microbial model. Collectively, these results illustrate the importance of soil characteristics to the biogeochemical and microbial response to both gradual climate change effects and extreme events. Furthermore, they show that large-scale decomposition models can be improved by adding microbial parameters. This information is relevant to the effects of climate change and microbial activity on biogeochemical cycles