The contrasting roles of host species diversity and parasite population genetic diversity in the infection dynamics of a keystone parasitic plant

1) Diversity among species and genetic diversity within species are both important components of ecological communities that can determine the outcome of species interactions, especially between hosts and parasites. We sought to understand the impact of species diversity on host community resistance to infection by a keystone parasitic plant (Rhinanthus minor L.) and genetic diversity of the parasite on its successful establishment in a grassland community. 2) We used an experimental approach where large pots were planted with mixtures of mesotrophic grassland species at high and low species diversity. The parasitic plant was sown in a proportion of these with high and low genetic diversity treatments. Establishment of the parasite was monitored over two years and the pots harvested at the end of each growing season to determine the impact of infection on plant community biomass. 3) We found a strong effect of host plant species diversity on the establishment of the parasitic plant, wit...