Increasing aridity reduces soil microbial diversity and abundance in global drylands

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Soil bacteria and fungi play key roles in the functioning of terrestrial ecosystems, yet our understanding of their responses to climate change lags significantly behind that of other organisms. This gap in our understanding is particularly true for drylands, which occupy ∼41% of Earth´s surface, because no global, systematic assessments of the joint diversity of soil bacteria and fungi have been conducted in these environments to date. Here we present results from a study conducted across 80 dryland sites from all continents, except Antarctica, to assess how changes in aridity affect the composition, abundance, and diversity of soil bacteria and fungi. The diversity and abundance of soil bacteria and fungi was reduced as aridity increased. These results were largely driven by the negative impacts of aridity on soil organic carbon content, which positively affected the abundance and diversity of both bacteria and fungi. Aridity promoted shifts in the composition of soil bacteria, with increases in the relative abundance of Chloroflexi and α-Proteobacteria and decreases in Acidobacteria and Verrucomicrobia. Contrary to what has been reported by previous continental and global-scale studies, soil pH was not a major driver of bacterial diversity, and fungal communities were dominated by Ascomycota. Our results fill a critical gap in our understanding of soil microbial communities in terrestrial ecosystems. They suggest that changes in aridity, such as those predicted by climate-change models, may reduce microbial abundance and diversity, a response that will likely impact the provision of key ecosystem services by global drylands.

This research is supported by the European Research Council (ERC) under the European Community's Seventh Framework Programme FP7/2007-2013/ERC Grant Agreement 242658 (BIOCOM); by Spanish Ministry of Economy and Competitiveness BIOMOD Project CGL2013-44661-R; and by Australian Research Council Project DP13010484. F.T.M. was supported by Salvador de Madariaga program of the Spanish Ministry of Education, Culture and Sports Grant PRX14/00225; the Research Exchange Program of the Hawkesbury Institute for the Environment; and a Research Award granted by the Alexander Von Humboldt Foundation. J.R.G. was supported by Iniciativa Científica Milenio PO5-002 (MIDEPLAN) and Comisión Nacional de Investigación Científica y Tecnológica PFB-23.

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