Nutrient addition in grasslands worldwide reveals proportional plant diversity decline across spatial scales but little change in beta diversity

Plant diversity decline under nutrient addition in local grassland communities is typically ascribed to the loss of rare species, species with particular traits ill-suited for high nutrient levels, and displacement of many localized species with a few widespread species. Whether these changes result in stronger diversity decline and vegetation homogenization at larger spatial scales (aggregated local communities) remains largely unknown. Using a standardized replicated fertilization experiment in 70 grasslands on six continents, we found proportional species loss at local and larger spatial scales but no vegetation homogenization under nutrient addition. Moreover, nutrient addition drove proportional species loss across spatial scales irrespective of species abundance, provenance, life form, or distribution. These results demonstrate that nutrient addition poses a potential threat to all plant functional groups including widespread dominant species that may be critical for ecosystem functions and services.