Field-based observational research is the first step in understanding the factors that structure microbial communities and generate biogeography of soil microbes. As one of the last remaining naturally grazed ecosystems on Earth, the Serengeti National Park in Tanzania is an ideal location to study the influence of large migratory mammals on microbial communities. Also, active volcanoes generate strong environmental gradients due to ash deposition and a rain shadow. We used 16S rRNA amplicons to characterize bacterial and archaeal communities in soils from a 13-year herbivore removal experiment to study the influence of grazing and environmental gradients on the natural distribution of soil microbes. Removal of mammalian herbivores shifted microbial community structure, with 31 amplicon sequence variants (ASVs) that were significant indicator taxa of the ungrazed treatment and only three ASVs that were significant indicators of the grazed treatment. The abundance of many ASVs were correlated with soil texture, phosphorus, iron, calcium and rainfall, and the evenness of taxa within samples increased with fine-textured soil. Bayesian general linear mixed effects models that parse the relative importance of multiple, highly correlated predictors of beta diversity were consistent with a significant, but weak (2%), effect of grazing, and stronger effects of phosphorus (14%) and silt (14%) contents in soil. Beta diversity of microbial communities was greater in grazed than in ungrazed plots; consequently, our results suggest that the impacts of grazing on the community assembly of microbes results from deterministic environmental filtering caused by the influence of herbivores on plant communities and soil properties rather than stochastic dispersal via herds of large mammalian herbivores. These herbivore effects are superimposed on deterministic environmental filtering by natural soil and precipitation gradients across the Serengeti.
|Date made available
|Sep 10 2020