Disentangling the influence of aridity and salinity on community functional and phylogenetic diversity in local dryland vegetation

Abstract

One of the key hypothesized drivers of community assembly and dynamics is environmental filtering, where environmental stress limits species migration and survival as a result of functional trait convergence. Whereas most such studies focus on large-scale variation in functional traits along a single-factor environmental gradient, the mutual effects of small-scale multiple environmental filtering remain unclear. Furthermore, it has rarely been tested whether the combined effect of aridity and salinity on local dryland vegetation constrains the patterns of functional traits and phylogenetic structures. Across an 8-km long transect in the arid northwest of China, we assessed the role of environmental filtering in shaping community assemblages by testing the hypotheses that aridity and salinity stresses, interspecific competition and phylogenetic structures constrained functional diversity in the local dryland vegetation. Our results showed that aridity significantly increased convergence of the maximum plant height, specific leaf area, leaf area and leaf nitrogen concentration. However, salinity significantly promoted the convergence of only leaf area and leaf nitrogen concentration. In addition, interspecific competition increased the convergence of the maximum plant height and leaf area. Leaf area converged significantly due to phylogenetic history. Aridity filtering, but not salinity filtering, obviously increased the clustering of phylogenetic structure. Interspecific competition and phylogenetic structure had weak effects on functional diversity in local dryland vegetation. In conclusion, compared with salinity filtering, aridity filtering was more important in reducing phylogenetic diversity in dryland vegetation.