Plant diversity effects on herbivory are mediated by soil biodiversity and plant chemistry

Abstract Insect herbivory is a key process in ecosystem functioning. While theory predicts that plant diversity modulates herbivory, the mechanistic links remain unclear. We postulated that the plant metabolome mechanistically links plant diversity and herbivory. In autumn and in spring, we assessed aboveground herbivory rates and plant metabolomes of seven plant species in experimental plant communities varying in plant species and resource acquisition strategy diversity. In the same plots, we also measured plant individual biomass as well as soil microbial and nematode community composition. Herbivory rates decreased with increasing plant species richness. Path modelling revealed that plant species richness and community resource acquisition strategy affected soil community composition. In particular, changes in nematode community composition affected plant metabolomes and thereby herbivory rates. These results provide experimental evidence that soil community composition plays an important role in reducing herbivory rates with increasing plant diversity by changing plant metabolomes.