Pervasive effect of dark septate fungi on tree root and soil microbiomes

Trees interact with a multitude of microbes through their roots and root symbionts such as mycorrhizal fungi and root endophytes. However, it remains unclear how these symbioses affect the structure and function of soil communities, which control key ecosystem processes such as organic matter decomposition and nutrient cycling. Here we test the importance of root colonization by ectomycorrhizal, arbuscular mycorrhizal, and dark septate endophytic fungi in shaping soil and root microbiomes of widespread broad-leaved trees, while accounting for climate, soil, and vegetation properties across a European latitudinal gradient. We found that dark septate endophyte colonization had a stronger and more consistent influence on the structure of root and soil microbiomes than mycorrhizal colonization and many abiotic factors. Our study demonstrates that biotic interactions at the root-soil interface are an important factor determining soil communities and functions in forest ecosystems, and that dark septate endophyte are likely to be central players in these interactions