Phylogenetic Clustering Reveals Selective Events Driving the Turnover of Bacterial Community in Alpine Tundra Soils

Soil bacterial communities play a determining role in snow-covered ecosystems' response to global warming because of their role in nutrient recycling. However, little is known about how changes in snow-cover dynamics could affect bacterial community assembly in the short or long term. We examined the phylogenetic structure of soil bacterial communities sampled seasonally from early snowmelt (ESM) and late snowmelt locations (LSM) in temperate alpine tundra. Most of the variation in phylogenetic structure (i.e. beta-diversity) was temporal rather than spatial and most observed deviations from random community assembly were towards phylogenetic clustering. Indeed, we observed phylogenetic clustering of Acidobacteria, Actinobacteria, and alpha-Proteobacteria during late winter in ESM locations, and a phylogenetic clustering of beta-,gamma-Proteobacteria, and Bacteroidetes during autumn in ESM and LSM locations probably linked to the onset of plant senescence and biomass decomposition. Interestingly, Acidobacteria were clustered in all LSM samples. Our study provides evidence of a high seasonal turnover of the phylogenetic structure of bacterial communities in alpine tundra soils, suggesting that climate-induced changes in snow cover can significantly alter the functioning of cold ecosystems through their filtering effects on soil bacteria communities.