Nonlinear relationship between diversity of rare and common species and ecosystem multifunctionality in alpine meadows along an altitude gradient

Biodiversity is closely related to ecosystem multifunctionality (EMF), and both are affected by environmental change. However, little is known about the impact of specific components of a biome (e.g., rare and common species) on EMF. This limits our understanding of protecting rare and common species and better utilizing multiple ecosystem services. In this study, we established 15 study plots at different elevation gradients (ranging from 2010 m to 3931 m) in the northeastern Tibetan Plateau to analyze the changes in species diversity of rare and common species in alpine meadows and their contributions to EMF. The results showed that (1) the functional richness (FRic), functional evenness (FEve), and species richness (SR) of rare species were significantly higher than those of common species. (2) The diversity of both rare and common species was significantly positively correlated with EMF across the entire elevation gradient, with the FRic of rare species explaining more of the variation in EMF (R-2 = 0.73, P < 0.001). (3) EMF showed a significant negative correlation with elevation (F = -14.67, P < 0.001), with elevation explaining 88 % and 81 % of the variation in EMF in the regions with elevation <3100 m and elevation >3100 m, respectively. (4) The relationship between rare species diversity and EMF changed around 3100 m above sea level. At lower altitudes (<3000 m), common species diversity was positively correlated with EMF, while at higher altitudes (>3150 m), the positive impact of rare species diversity on EMF was more significant. This study helps to understand more carefully how rare and common species affect EMF in the context of climate change and, for the first time, emphasizes the potential and role of rare species in predicting and regulating ecosystem functions, productivity, and functional trade-offs. It is recommended to designate alpine meadow areas as protected areas, strengthen the protection of rare species in high-altitude meadows, and establish seed banks of rare species for artificial restoration. In low-altitude regions, the diversity of common species should be maintained through reasonable grazing, grazing bans and rotations, and organic fertilizers.