Disentangling the seasonal dynamics of biodiversity-productivity relationships:the role of species evenness in a subtropical forestOA

Understanding the degree to which the species diversity-productivity relationship(SDPR)is applicable to natural ecosystems-beyond modeling and experimental contexts-is of vital importance for comprehending the conse-quences of global biodiversity loss on terrestrial ecosystems.Two essential features of natural forests that have not received adequate attention in the SDPR are seasonality and species evenness.Here,we monitor the intra-and inter-annual growths of 6,515 trees in a subtropical seasonal(temperature-and rainfall-seasonal)forest over a six-year period.We investigate whether evenness affects forest productivity independently or interacting with richness and how the underlying mechanisms shift with seasonality and soil properties,employing structural equation modeling.Our findings reveal a consistent decline in species diversity,functional diversity and forest productivity from the wet-warm season to the dry-cold season,with community traits shifting from acquisition to conservative strategies.Species richness increases but evenness decreases forest productivity-uneven commu-nities are more productive,and the attenuation effect of evenness on productivity varies slightly across different seasons.Species richness and evenness jointly affect productivity through community-weighted means(CWM)of functional traits in the wet-warm season and through both functional diversity and CWM of functional traits in the dry-cold season,indicating that the mass ratio effect is predominant during the wet-warm season,whereas both niche complementarity and mass ratio effects jointly drive productivity in the dry-cold season.Soil water availability directly affects forest productivity in the wet-warm season and indirectly through CWM of functional traits in the dry-cold season.Our study,the first to elucidate the seasonal dynamics of the SDPR in subtropical forests.Our results highlight species evenness as a key component of species diversity regulating seasonal pro-ductivity dynamics in heterogeneous,species-rich natural forests.To enhance forest resilience under climate change(e.g.,drought),management should prioritize maintaining moderate evenness,while strategically planting drought-tolerant species and acquisitive species of subtropical forest ecosystems.