Selection for monoculture and mixture genotypes in a biodiversity experiment

Studies in experimental grasslands have shown variation in plant individual performance in response to neighbourhood diversity. To which extent these responses are due to phenotypic plasticity or genetic variation is largely unknown. We collected seed families of five herbaceous species (Cirsium oleraceum, Crepis biennis, Plantago lanceolata, Plantago media and Rumex acetosa) in monocultures and 60-species mixtures 5 years after establishment and replanted or transplanted the offspring into the same monocultures and 60-species mixtures. In all five species the actual environment significantly affected plant survival, growth and performance in terms of shoot biomass and investment into reproduction, indicating stronger competition for light and different levels of herbivory in mixtures as compared with monocultures. Effects of the original environment were smaller and less consistent, but indicated differential selection in monocultures vs. mixtures. The interaction between actual and original environment, corresponding to the “home” vs. “away” comparison, was rarely significant, yet this was providing a first sign of local adaptation. We conclude that, for the investigated plant species, more than five growing seasons in monocultures or mixtures would be needed to better demonstrate the selection of genotypes specifically adapted to monocultures or mixtures. A faster local adaptation may have been prevented by the ability of these species to respond to variation in neighbourhood diversity to a large degree via phenotypic plasticity and other factors.