Environmental factors drive the functional and phylogenetic meadow communities’ assembly in the northeastern Tibetan Plateau

Background/Question/Methods: Understanding community assembly processes is a central theme in plant ecology. Tibetan meadows are among the most impacted ecosystems facing the selection pressures caused by extreme climate, making they an ideal system to examine the dynamics and mechanisms driving plant community assembly. Yet, alpine meadow have received surprisingly little research attention. Traditional community assembly theory assumes species partition their niche space, which promotes coexistence. To understand the filters influencing community assembly, We examined the functional and phylogenetic structure of 170 alpine Tibetan meadow communities in relation to elevation, soil moisture and shade. Functional community structure was estimated with both community-weighted mean (CWM) trait values for specific leaf area (SLA), plant height and seed mass and functional diversity (Rao’s quadratic index) for their traits individually and in combination (multivariate functional diversity).

Results/Conclusions: We found that shade induced by woody plants significantly increased the phylogenetic diversity and functional diversity of SLA of co-occurring species, suggesting that woody plants behave as “ecosystem engineers” creating a different environment that allows the existence of shade tolerant species and thereby facilitates the coexistence of plant species with different light resource acquisition strategies. We also found that both drought and excess moisture may act as environmental filters selecting species with close phylogenetic relationships and similar height. Finally, we detected that the multivariate functional diversity did not change across environmental gradients. This lack of multivariate response supports the hypothesis that multiple processes, such as environmental filtering, competition and facilitation, may operate simultaneously and exert opposing effects on community assembly along different niche (e.g. water use, light acquisition) axes, resulting in no overall functional community structure change. This contrast between individual and multivariate trait patterns highlights the important of examining individual traits linked with different ecological processes to better understand the mechanisms of community assembly.