Consistent predictors of microbial community composition across spatial scales in grasslands reveal low context-dependency

Environmental circumstances shaping soil microbial communities have been
studied extensively. However, due to disparate study designs, it has been
difficult to resolve whether a globally consistent set of predictors
exists, or context-dependency prevails. Here, we used a network of 18
grassland sites (11 of those containing regional plant productivity
gradients) to examine i) if similar abiotic or biotic factors predict both
large-scale (across sites) and regional-scale (within sites) patterns in
bacterial and fungal community composition, and ii) if microbial community
composition differs consistently at two levels of regional plant
productivity (low vs high). We found that bacteria were consistently
associated with certain soil properties and both bacteria and fungi were
consistently associated with plant community composition within different
sites. Moreover, there was a microbial community signal that clearly
distinguished high and low-productivity soils that was shared across
different grasslands independent of their location in the world. In this
study, we show that there is high congruence between predictors of
bacterial and fungal community composition at different spatial scales and
that regional productivity differences are typified by characteristic soil
microbial communities across the grassland biome. These results suggest
that it might be feasible to predict the overall effects of global changes
on soil microbial community composition in different grasslands, as well
as to discriminate fertile from infertile systems using generally
applicable microbial indicators.