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ABSTRACT 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. 

ABSTRACT Although biodiversity is widely recognised for its role in maintaining ecosystem functioning under environmental change, its importance has received relatively little attention in the context of emerging environmental stressors such as nanoparticles. By assembling phytoplankton communities across a gradient of species richness and exposing them to varying concentrations of copper oxide nanoparticles, we experimentally explored how biodiversity modulates ecosystem functioning under nanoparticle exposure. We found that the positive effect of biodiversity on phytoplankton biomass production was amplified at higher nanoparticle concentrations, allowing diverse communities to maintain biomass despite strong inhibitory effects of nanoparticles on monocultures. This enhanced biodiversity effect was primarily driven by increased complementarity, specifically through more frequent facilitative interactions among species under nanoparticle stress. Our findings advance the understanding of how biodiversity preserves ecosystem functioning and underscore its role in mitigating the impacts of emerging anthropogenic stressors.