Lost in diversity: the interactions between soil-borne fungi, biodiversity and plant productivity

There is consensus that plant species richness enhances plant productivity within natural grasslands, but the underlying drivers remain debated. Recently, differential accumulationof soil-borne fungal pathogensacross the plant diversity gradient has been proposed as a cause of this pattern. However, the below-ground environment has generally been treated as a ‘black box’ in biodiversity experiments, leaving these fungi unidentified. * Using next generation sequencing and pathogenicityassays, we analysed the community composition of root-associated fungi from a biodiversity experiment to examine if evidence exists for host specificity and negative density dependencein the interplay between soil-borne fungi, plant diversity and productivity. * Plant species were colonised by distinct ( pathogenic) fungal communities and isolated fungal species showed negative, species-specific effects on plant growth. Moreover, 57% of the pathogenicfungal operational taxonomic units(OTUs) recorded in plant monocultureswere not detected in eight plant species plots, suggesting a loss of pathogenicOTUs with plant diversity. * Our work provides strong evidence for host specificity and negative density-dependenteffects of root-associated fungi on plant species in grasslands. Our work substantiates the hypothesis that fungal root pathogensare an important driver of biodiversity-ecosystem functioning relationships.