Rainfall and Soil Moisture Jointly Drive Differences in Plant Community Composition in Desert Riparian Forests of Northwest China

Extreme rainfall and soil moisture play important roles in the survival, community composition, and ecosystem function of desert plants. This study focused on arid desert riparian forests ecosystems in the Ebinur Lake Basin of Xinjiang, China. We analyzed the effects of rainfall and soil moisture on species composition, indicator species, β diversity, species turnover, and nestedness using three consecutive years of community surveys. A zero-model combined with a Bayesian framework was used to explore the response of species turnover and nestedness to soil moisture and rainfall, and variance decomposition was used to quantify the relative importance of spatial distance, rainfall, and soil factors in determining species composition. The results indicated the following: (1) when rainfall was high, the richness and abundance of annual herbaceous plants increased. The proportion of the community based on richness (32%) and abundance (58.1%) of annual herbaceous plants in 2016 was higher than that in 2015 and 2017. The Jaccard, Bray–Curtis, and Chao indexes of the community in years with higher rainfall were significantly higher than in years with lower rainfall; however, a lag effect was also observed. (2) Soil factors explained 5% of the changes in community composition, rainfall explained 12% of the changes in community composition, and spatial distance, soil factors, and rainfall jointly explained 32% of the changes in community composition. (3) We also showed that high soil moisture leads to greater β diversity than low soil moisture. Rainfall had the greatest explanatory power on the measured values of β diversity (19.6%) and species turnover (38%), and the factor with the greatest explanatory power for species nestedness was the interaction between rainfall and soil moisture (26.2%). Our findings indicate that drought and rainfall drive differences in plant community composition, with rainfall playing a dominant role. These results provide a basis for understanding the impact of extreme rainfall events on arid ecosystem functions.