Changes in the functional trait composition and diversity of meadow communities induced by Rhinanthus minor L.

Rhinanthus minor L. is a root hemiparasite with known effects on community productivity and species composition. It is unclear, though, how these effects operate on functional trait composition and functional diversity. To fill this gap we established an experiment in a meadow community with a natural Rhinanthus population, where Rhinanthus presence (removal vs no removal) was manipulated under fertilized and unfertilized conditions. We assessed the biomass of individual species at the scale where plant individuals interact, in 20 cm x 20 cm plots. The community trait composition was characterized by community weighted means (CWM) and Rao's quadratic entropy (as an index of functional diversity). Given the expected differences in the response to Rhinanthus parasitism, these parameters were computed for the whole community, for grasses (Poaceae family) and for forbs (non-leguminous dicots) separately. Generally, the species favoured by Rhinanthus were those with low competitive ability (with a low height, a low capacity for clonal growth, a taproot during the whole lifecycle, were monocyclic and had low leaf dry matter content). Rhinanthus increased functional diversity for clonality, which indicated a better coexistence of species with various capacities for clonal growth. CWM and functional diversity of grasses were not affected. Among the forbs, Rhinanthus mainly suppressed the tall, clonal species without a taproot (those which are functionally similar to grasses). Fertilization also affected CWM and functional diversity, but without significant interaction with Rhinanthus. We conclude that functional traits highlight the processes by which Rhinanthus affects vegetation structure and species coexistence.