Effect of Changing Precipitation Timing on Phylogenetic and Functional Community Structure in A Semi-Arid Steppe

Abstract Changes in the amount and timing of precipitation may affect plant species coexistence. However, little is known about how these changes in precipitation structure plant communities. Here, we conducted a six-year field precipitation manipulation experiment in the semi-arid steppe of Inner Mongolia, China to assess the importance of species loss and colonization to community assembly by incorporating phylogenetic information on functional relatedness. Our results demonstrated that the decline in plant species richness under decreasing precipitation in the late and entire growing season could be attributed to a decrease in species colonization and an increase in species loss, respectively. The increase in species richness under increasing precipitation in the late growing season was mainly caused by increases in colonizing species. Species with lower initial abundances, individual size, and leaf dry matter content had greater loss probabilities when species with lower initial abundances had greater colonization likelihood. The loss of species that were more closely related to other residents under decreasing precipitation in the late growing season did not alter phylogenetic overdispersion patterns, and the colonization of species that were more distantly related to residents under increasing precipitation in the late growing season shifted functional relatedness from clustering to randomness. Thus, the colonization of functionally dissimilar species decreased the strength of environmental filtering. Our study showed that phylogenetic and functional relatedness independently affected plant community structure. This finding suggests that evolutionary processes affect community assembly independently of ecological processes.