Environmental and biotic drivers of soil microbial β-diversity across spatial and phylogenetic scales

Soil microbial communities play a key role in ecosystem functioning but still little is known about the processes that determine their turnover (beta-diversity) along ecological gradients. Here, we characterize soil microbial beta-diversity at two spatial scales and at multiple phylogenetic grains to ask how archaeal, bacterial and fungal communities are shaped by abiotic processes and biotic interactions with plants. We characterized microbial and plant communities using DNA metabarcoding of soil samples distributed across and within eighteen plots along an elevation gradient in the French Alps. The recovered taxa were placed onto phylogenies to estimate microbial and plant beta-diversity at different phylogenetic grains (i.e. resolution). We then modeled microbial beta-diversities with respect to plant beta-diversities and environmental dissimilarities across plots (landscape scale) and with respect to plant beta-diversities and spatial distances within plots (plot scale). At the landscape scale, fungal and archaeal beta-diversities were mostly related to plant beta-diversity, while bacterial beta-diversities were mostly related to environmental dissimilarities. At the plot scale, we detected a modest covariation of bacterial and fungal beta-diversities with plant beta-diversity; as well as a distance-decay relationship that suggested the influence of ecological drift on microbial communities. In addition, the covariation between fungal and plant beta-diversity at the plot scale was highest at fine or intermediate phylogenetic grains hinting that biotic interactions between those clades depends on early-evolved traits. Altogether, we show how multiple ecological processes determine soil microbial community assembly at different spatial scales and how the strength of these processes change among microbial clades. In addition, we emphasized the imprint of microbial and plant evolutionary history on today's microbial community structure.