Emergent properties of microbial communities drive accelerated biogeochemical cycling in disturbed temperate forests

Despite ever-increasing availability of detailed information about microbial community structure, relationships of microbial diversity with ecosystem functioning remain unclear. We investigated these relationships at the Coweeta Hydrologic Laboratory, where past forest disturbances (e.g., clear-cut) have altered both ecosystem processes (e.g., increased N export) and microbial communities (e.g., increased bacterial diversity). We sampled soils from disturbed and adjacent reference forests, characterized resident microbial communities, and measured several microbial C-cycle and N-cycle process rates. Microbial communities from historically disturbed soils exhibited altered ecosystem functioning, including generally higher rates of C- and N-cycle processes. Disturbed soil microbial communities also exhibited altered ecosystem multifunctionality, a composite variable consisting of all measured process rates as well as extracellular enzyme activities. Although we found few relationships between ecosystem functions and microbial alpha diversity, all functions were correlated with microbial community composition metrics, particularly r:K strategist ratios of bacterial phyla. Additionally, for both ecosystem multifunctionality and specific processes (i.e., C- and N-mineralization), microbial metrics significantly improved models seeking to explain variation in process rates. Our work sheds light on the links between microbial communities and ecosystem functioning and identifies specific microbial metrics important for modeling ecosystem responses to environmental change.