Inferring community assembly mechanisms from functional and phylogenetic diversity: The relative contribution of environmental filtering decreases along a sand desertification gradient in a desert steppe community

Abstract

AbstractThe stress‐dominance hypothesis (SDH) predicts that environmental filtering will dominate in harsh habitats, while limiting similarity is more important in favourable environments. Here, we test the generality of the SDH to disentangle the relative importance of these two ecological processes along a sand desertification gradient. Data were collected from randomly selected locations in a desert steppe community in Northwest China. In this region, intense habitat fragmentation has resulted in a series of original soil habitat patches called soil islands. These soil islands typically contain Sierozem soils historically subjected to low (L), medium (M), and high (H) levels of sand desertification. Along this sand desertification gradient, soil properties and leaf traits (LDMC, leaf dry matter content; SLA, specific leaf area; LC, leaf carbon concentration; LP, leaf phosphorus concentration; and LN, leaf nitrogen concentration) were measured. We then tested for trait and phylogenetic convergence or divergence using a null model approach. Along the sand desertification gradient, trait convergence trend decreased, while trait divergence trend increased. Similarly, the phylogenetic convergence trends decreased. Traits displaying convergence included LDMC, SLA, and LCC, while LP and LN displayed divergence. The strength of LDMC convergence was negatively correlated with community weighted mean trait values (CWM) for LDMC. In contrast, the strength of LN divergence was positively correlated with CWM for LN. Our results pertaining to LDMC and LN support the SDH. Along the sand desertification gradient, the strength of environmental filtering gradually decreased, while the intensity of limiting similarity gradually increased.