Shedding Light on a Problem: Human activities—mainly the application of fertilizers to farmland—have increased the availability of nutrients in terrestrial and aquatic ecosystems. In grasslands, nutrient enrichment reduces plant species diversity, but the mechanisms underlying this loss of biodiversity remain unclear. Hautier et al. (p. 636 ) use an experimental manipulation, addition of supplementary light to the grassland understory, which supports the idea that competition for light is the major mechanism of plant diversity loss.

Biodiversity protects grassland stability: How biodiversity interacts with ecosystem stability and productivity is key to understanding the impacts of environmental changes on ecosystem functions. In a series of decade-long experiments in temperate grassland, Hautier et al. manipulated nitrogen, water, carbon dioxide, herbivory, and fire. In all cases, plant species diversity was important for preserving ecosystem function during environmental change. Hence, the preservation and restoration of biodiversity buffer ecosystems against anthropogenic assault. Science , this issue p. 336