Soil microbes are diverse, ubiquitous and abundant, yet our understanding of their biogeographical patterns is extraordinarily limited. Environmental heterogeneity and dispersal limitation are clearly both key determinants of biogeographical patterns in animals and plant species. Dispersal limitation is considered to be less important for microorganisms, resulting in biogeographical patterns that primarily reflect selection by contemporary environmental conditions. However the influence of dispersal limitation in determining microbial biogeographical patterns at the regional and global scales has not yet been fully evaluated because of the lack spatially explicit studies at these scales. Arctic soils provide an ideal testbed for understanding the patterns and controls on microbial biogeography because they are subject to particularly severe environmental stresses that may have produced unique and distinct bacterial communities compared to those found in lower latitudes.

Results/Conclusions Here we show that arctic soil bacterial community composition and diversity are structured according to local variation in soil pH rather than geographical proximity to neighboring sites, suggesting that local environmental heterogeneity is far more important than dispersal limitation in determining community-level differences. Furthermore, bacterial community composition varied as much within arctic soils as across soils from a wide range of lower latitude biomes, and diversity levels were also similar, indicating global similarities in the structure of soil bacterial communities. These results contrast with the well-established latitudinal gradients in animal and plant diversity, suggesting that the controls on bacterial community distributions are fundamentally different from those observed for macro-organisms and that our biome definitions are not useful for predicting variability in soil bacterial communities across the globe.