Prolonged Nutrient Enrichment Slows the Recovery of Biodiversity and Productivity After Its Cessation

Many ecosystems worldwide are experiencing chronic anthropogenic nutrient enrichment, which often increases plant productivity while reducing species richness. Although nutrient inputs are now declining in some regions, the potential benefits of this reduction depend on the reversibility of enrichment impacts. In turn, ecosystem recovery can be determined by the enrichment history, that is, the rate and duration of nutrient enrichment. Here, we quantify how nutrient enrichment history shapes community recovery dynamics using a four-decade grassland experiment that examines the joint effects of nutrient enrichment rate and duration with: (1) three durations of nutrient enrichment and recovery: one decade of enrichment followed by three decades of recovery, three decades of enrichment followed by one decade of recovery, or continuous enrichment for four decades; and (2) nutrient enrichment at a gradient of rates ranging from atmospheric deposition to agricultural fertilization. Our results showed nutrient enrichment increased plant biomass and reduced species richness, with higher nutrient addition rates leading to more rapid and sustained species loss and biomass increase, even over short enrichment periods. We assessed recovery dynamics following cessation as increases in species richness and declines in community biomass relative to control conditions, because of the tight coupling between richness and biomass in many communities. We found that the reversibility of enrichment effects depended on enrichment duration, with prolonged enrichment slowing recovery of both species richness and biomass, especially at high enrichment rates. However, biomass recovered more rapidly than species richness following cessation. These findings highlight that recovery trajectories of biodiversity and ecosystem functioning depend jointly on enrichment rate and duration, underscoring the need for restoration strategies that account for nutrient legacies and their determinants.