Community phylogenetic structure of grasslandsand its relationship with environmental factors on the Mongolian Plateau

The community assembly rules and species coexistence have always been interested by ecologists.The community phylogenetic structure is the consequence of the interaction process between the organisms and the abiotic environmentand has been used to explain the relative impactof abiotic and biotic factors on species co-existence. In recent years, grassland degradation and biodiversity loss have become increasingly severe on the Mongolian Plateau,while the drivers for these changes are not clearly explored, especially whether climate change is a main factor is debated in academia. In this study, we examined the phylogenetic structure of grassland communities along five transects of climate aridity on the Mongolian Plateau, and analyzed their relations with environmental factors, with the aims to understand theformation mechanismof the grasslandcommunities and the role of climatic factors.We surveyed grassland communities at 81 sites along the five transects,and calculated theirnet relatedness index (NRI)attwo different quadratscales (smallscale of 1 m² and largescale of 5 m²) to characterize thecommunity phylogenetic structure andanalyzeitsrelationship withthe key 11 environmental factors. We also calculatedthe generalized UniFrac distance (GUniFrac)among the grassland communities to quantify the influence of spatial distance and environmental distance on the phylogenetic β diversity. The results indicated that plant community survey using the largescalequadrat contained sufficient species to represent community compositions. The community phylogenetic structure of grasslandswas significantly overdispersed at both the small and largescales, and the degree of overdispersion was greater at the large scalethan at the smallscale, suggesting that competitive exclusion instead of habitat filtering played a major role in determination of community composition. Altitude was the main factor affecting the community phylogenetic structure, whereas climatic factors, such as precipitation and temperature, had limited influence. Theprincipal component analysis of the 11 environmental factorsrevealed that 94.04% of their variation was accounted by the first four principal components.Moreover only 14.29% and 23.26% of the variation in community phylogenetic structurewere explained by the first four principal componentsat the small and largescales, respectively. Phylogenetic β diversity was slightly significantly correlated with both spatial distance and environmental distance, however,environmental distancehada less explanatory powerthan spatial distance, indicating a limited environmental effect on the community phylogenetic structure of grasslands on the Mongolian Plateau. In view of the limited effect of climatic factors on the community phylogenetic structure of grasslands, climate change may have a smaller impact on grassland degradation than previously thought.