Plant species diversity and functional diversity relations in the degradation process of desert steppe in an arid area of northwest China

Species and functional diversity play a major role in the stability and sustainability of grassland ecosystems. However, changes in species and functional diversity during grassland degradation in arid areas as well as the underlying mechanisms remain unclear. In this study, we surveyed the vegetation and soil properties of arid regions across a degradation gradient to explore the shifts in species and functional diversity in plant communities, their relationships and key determinants during desert steppe degradation. Our results found significant variability in species diversity and functional diversity across degradation stages. Species diversity (Shannon-Wiener index (H), and Pielou index) and functional diversity (functional evenness (FEve) index, and Rao's quadratic entropy (RaoQ) index) tended to increase initially and then decrease with increasing grassland degradation. The Patrick index, Simpson index, functional richness (FRic) index, functional divergence (FDiv) index, and functional dispersion (FDis) index declined as grassland degradation increased. The relationships between species diversity and functional diversity indices at different stages of degradation in the desert steppe were inconsistent. From no to heavy degradation grasslands, the correlation between species diversity and functional diversity gradually weakened. Specifically, there was a significant correlation between Patrick (R) and FRic indices (R