Abstract
Fungal diversity influences both plant diversity and ecosystem functioning, but how fungi mediate the relationship between plant diversity and ecosystem multifunctionality is not as well understood. To address this knowledge gap, we manipulate plant species richness and soil fungal diversity (via fungicide addition) in 190 experimental plant communities and measure ten ecosystem functions to assess ecosystem multifunctionality. We find that reduced fungal diversity (via fungicide addition) decreases ecosystem multifunctionality, but only in plant communities with low species richness, indicating that soil fungal diversity can buffer the effects of plant diversity loss on ecosystem multifunctionality. Selection effects (i.e., superiority of dominant plant species) and phylogenetic clustering of the fungal community (i.e., functional redundancy) increase with plant species richness when fungicide is added, revealing potential mechanisms through which species-rich plant communities can mitigate the negative effects of reduced fungal diversity and maintain ecosystem multifunctionality. Our study emphasizes the importance of interactions between plant and fungal diversity for ecosystem multifunctionality, and highlights the need to conserve fungal diversity, especially in ecosystems with low plant diversity that are threatened by global change.