Plant functional diversity does not dilute virus infection, but community virus prevalence positively correlates with net C₃ grass production

Plant diversity in wild and agricultural plant communities has been shown to protect plant communities from pathogens, and the effects of many aspects of diversity (genetic diversity, species richness, evenness and their combination) on plant pathogen epidemiology have been examined. Diversity among plant functional groups (e.g. grasses, legumes and non-leguminous forbs) is known to reduce plant diseases in natural and agricultural plant communities. However, potential interactions among plant functional groups and their effects on plant virus infection dynamics have not been examined. Insect-vectored plant virus infection dynamics may differ among distinct plant host functional types (C₃ vs C₄) due to differences in their palatability to aphid vectors and plant physiological responses to environmental factors. Here, we evaluated the role of plant functional group diversity (richness and composition), and host functional type (three C₃ and three C₄ species) on plant virus infection in experimental annual plant communities that were inoculated with aphids carrying barley yellow dwarf virus (BYDV), a widespread and economically important generalist grass virus. We also assessed the relationships between community-level virus prevalence and the productivity of the total community (grasses + forbs + legumes), as well as the component plant functional types. In this study, virus infection was not mitigated or amplified by increasing functional group richness or altered functional group composition, nor did virus infection vary between C₃ and C₄ grasses. However, we found a positive correlation between community-level virus prevalence and C₃ grass production (but not C₄ production). Synthesis. Our findings indicated that plant virus infection in grasses was not diluted by plant functional group diversity. However, we found a positive relationship between community-level virus prevalence and C₃ grass productivity. Together, these findings suggest that while plant diversity did not reduce the infection levels of a cryptic plant virus, mutualistic plant–virus interactions may contribute to enhanced ecosystem functioning via increased productivity.