Soil microbial community structure and allocation are critical drivers of ecosystem functioning
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The functioning of terrestrial ecosystems is entirely dependent on the activity of autotrophic primary producers and microbial decomposers, and how they are affected by climate, mineralogy and anthropogenic change. Ecosystem ecology has classically focused on how allocation and community composition of plant primary producers may alter predictions of future ecosystem functioning in the face of environmental change. Little attention has been paid to allocation and community composition of microbial decomposers. The functioning of microbial decomposers has been considered implicitly, in the context of plant traits; primarily plant biomass chemistry. However, soil microbial communities represent a vast diversity of taxa spanning multiple kingdoms of life and an array of functional groups. It is not only likely, but probable that understanding ecological aspects of soil microbial community structure, activity, and allocation will fundamentally change how we understand and predict ecosystem function in the future. In chapters 1-3 of this dissertation, I explicitly considered how microbial activities varied based on microbial community structure and the resulting impacts for biogeochemical cycling. Specifically, in chapters 1 and 2, I manipulated the relative abundance of symbiotic root fungi to demonstrate that competition between symbionts and free-living decomposers for nitrogen slowed soil carbon cycling. In chapter 3, I scaled how nitrogen is partitioned between plants, mycorrhizas and free-living decomposer microbes to demonstrate how shifts in microbial community structure could explain how forests productivity is sustained over centuries. In chapter 4, I developed a microbial allocation framework that explicitly considers microbial resource environments. I demonstrated that past microbial allocation frameworks based on plant ecological mechanisms cannot explain allocation patterns of decomposer microbial life. Throughout this dissertation I attempt to put soil microbial life in an explicit ecological context that challenges current understanding of ecosystem process and will allow for deeper understanding and prediction of ecosystem functioning. Incorporating microbial community structure, allocation, and simple ecological mechanisms into models will improve the predictive power of ecosystem ecology.