The effects of environmental stress and mutualisms on relationships between biodiversity and ecosystem functioning in dune plant communities
Biodiversity can affect ecsosystem functioning through niche complementarity or positive interactions among species and by more diverse cultures including species with particular traits. Here, we tested whether the mechanism by which diversity influences functioning and the importance of mutualisms change with environmental stress. We planted monocultures of three dune grasses (Uniola paniculata, Spartina patens, and Panicum amarum) and the complete mixture in a factorial design that resulted in four treatmentss consisting of both the presence and absence of mycorrhizae and fertilizer.
We found that, aboveground, diversity increased biomass production in treatments with fertilizer and mycorrhizae by increasing the biomass of the largest plant species. This suggests that fertilizer collapsed niche space aboveground and the best competitor for light dominated. Belowground, however, complementarity among species increased overall root mass in fertilized treatments and no species dominated. Our results suggest that the environment and context of interspecific competition can determine how biodiversity influences ecosystem functioning.