Spatial and temporal turnover of soil microbial communities is not linked to function in a primary tropical forest.

The spatial and temporal linkages between turnover of soil microbial communities and their associated functions remain largely unexplored in terrestrial ecosystems. Yet defining these relationships and how they vary across ecosystems and microbial lineages is key to incorporating microbial communities into ecological forecasts and ecosystem models. To define linkages between turnover of soil bacterial and fungal communities and their function we sampled fungal and bacterial composition, abundance, and enzyme activities across a 3-ha area of wet tropical primary forest over 2 yr. We show that fungal and bacterial communities both exhibited temporal turnover, but turnover of both groups was much lower than in temperate ecosystems. Turnover over time was driven by gain and loss of microbial taxa and not changes in abundance of individual species present in multiple samples. Only fungi varied over space with idiosyncratic variation that did not increase linearly with distance among sampling locations. Only phosphorus-acquiring enzyme activities were linked to shifts in septate, decomposer fungal abundance; no enzymes were affected by composition or diversity of fungi or bacteria. Although temporal and spatial variation in composition was appreciable, because turnover of microbial communities did not alter the functional repertoire of decomposing enzymes, functional redundancy among taxa may be high in this ecosystem. Slow temporal turnover of tropical soil microbial communities and large functional redundancy suggests that shifts in abundance of particular functional groups may capture ecosystem function more accurately than composition in these heterogeneous ecosystems.