Soil microbes and biogeography: Are communities from differing environments functionally equivalent?

The role and importance of biogeographical factors, such as historical contingency and habitat, on microbial community function is largely unexplored. If everything is everywhere and the environment selects, as is commonly proposed for microbial communities, then we might expect that inoculums from different habitats and/or distinct geographic areas would function similarly when placed in a common environment. We tested these assumptions via two experiments. In the first we compared how soil inoculums from three geographic regions (Sedgewick Reserve, Coweeta LTER, Duke Forest) affected carbon mineralization rates of foliar litters collected from each region. In the second we compared microbial community function, again measured as mineralization rates, when soils were sourced from a single geographic region (Calhoun Experimental Forest), but markedly different habitats, and inoculated onto novel litter resources maintained under common conditions. In the first experiment mineralization rates followed a similar pattern, defined by a rapid initial peak in mineralization rates (1-25 days), an extended secondary peak (25-100 days), and finally a decline phase (100-300 days). The point at which each stage occurred and the length of each stage differed between inoculums; furthermore, inoculums exposed to litter from their home region showed higher, cumulative mineralization rates, suggesting a “home advantage”. In the second experiment habitat markedly influenced mineralization dynamics. As in the first experiment, variance across replicates was low, while treatment effects were significant. Together, results from these studies suggest that there is marked biogeography in microbial community function that arises from both historical contingency and habitat.