Lost in trait space: species-poor communities are inflexible in properties that drive ecosystem functioning

It is now well established that biodiversity plays an important role in determining ecosystem functioning and its stability over time. A possible mechanism for this positive effect of biodiversity is that more diverse plant communities have a greater capacity to respond to environmental changes through shifts in species dominance and composition. In our study, we utilized data from five long-term grassland biodiversity experiments located in North America (three studies) and Central Europe (two studies), in which plant species richness and global change drivers were manipulated simultaneously. The global change drivers included warming, drought, elevated atmospheric CO₂ concentrations, elevated N inputs, or intensive management. Across drivers, functional change over time was significantly greater for communities of high plant diversity than that of low diversity because of a higher functional and phylogenetic richness and mostly associated with a dominance by species with a ‘slow and tall’ strategy. Community functional shifts in response to global change drivers were, however, relatively weak and mostly not influenced by diversity. The exception to this was warming, where diverse communities showed stronger shifts than species-poor communities. Our results confirm the hypothesis that diverse communities have a greater capacity for functional change than species-poor communities, particularly in their successional dynamics, but also potentially in their responses to environmental change. This capacity could underlie the positive biodiversity-stability relationship and buffer ecosystem responses to environmental change.