Plant compositional dynamics explain the destabilizing effect of eutrophication on grassland productivity

Abstract Biodiversity can stabilize ecosystem functioning, yet this relationship is often weakened under environmental change such as nutrient enrichment. The mechanisms underlying this weakening remain unclear, particularly whether it arises from shifts in species that consistently contribute to community dynamics or from increased species turnover. Species that persist through time are expected to underpin stability by maintaining species stability and asynchronous dynamics, whereas transient species, characterized by low temporal occupancy, primarily contribute to compositional turnover with limited stabilizing effects. Disentangling the roles of these two groups may therefore explain how nutrient enrichment alters biodiversity–stability relationships. Using data from 49 grasslands with and without fertilization, we partitioned communities into persistent and transient species based on temporal occupancy. We quantified their respective contributions to community temporal stability and evaluated how fertilization altered the relationships between species richness, species asynchrony, species stability and community stability using structural equation models. Community stability was primarily driven by persistent species: communities with more stable and asynchronous persistent species exhibited higher temporal stability. In unfertilized conditions, species richness was positively associated with the stability and asynchrony of persistent species, as well as with the asynchrony between persistent and transient species, which were linked to higher community stability. Under fertilization, these pathways were weakened, as fertilization reduced persistent species stability and persistent–transient asynchrony, resulting in lower community stability. Transient species contributed little to stability in either condition and may obscure biodiversity–stability relationships when not explicitly accounted for. Synthesis . These results indicate that biodiversity–stability relationships are mediated predominantly by species that persist through time, consistent with theoretical expectations that invariability emerges from stable and asynchronous population dynamics. Nutrient enrichment weakens these relationships by disrupting the stabilizing role of persistent species rather than by increasing the contribution of transient species. Accounting for species temporal persistence thus provides a mechanistic basis for predicting how global change alters ecosystem stability.