Nutrient enrichment negatively impacts flowers and pollinators, especially in warmer climates

Human-driven nutrient enrichment is reducing grassland plant diversity, yet the consequences of these changes for floral resources and pollinators remain poorly understood. Using a long-term fertilization experiment replicated at 14 sites spanning three continents, we show that the effect of nitrogen (N) input on pollinators and their resources depends on local climate and soil type. In naturally nutrient-rich soils (e.g. temperate European grasslands), N input always reduced floral resource availability, especially in warmer climates where pollinator activity declined. In nutrient-poor soils (e.g. Brazilian Cerrado, Mediterranean grasslands), N did not always reduce floral resources but it had a general negative effect on pollinator activity in warmer climates. Nutrient enrichment effects were greater on pollinators than on plants. These results indicate that biodiversity in warmer regions faces greater risks from environmental eutrophication.