Abstract:

Aims: Uncovering the assembly mechanism that shapes the large-scale biodiversity patterns is a key challenge in ecology. Numerous previous studies have demonstrated that multiple ecological processes can simultaneously regulate plant community assembly. However, how they shape the plant taxonomic, functional, and phylogenetic β-diversity of gobi deserts remains unclear, hindering the understanding of gobi plant assembly processes and diversity maintenance.
Methods: We selected 61 sites from major gobi desert habitat types across northern Qinghai-Tibet Plateau. Plant species abundance, molecular phylogeny, as well as eight functional traits including: leaf nitrogen concentrations (LNC), leaf phosphorus concentrations (LPC), leaf area (LA), specific leaf area (SLA), fine root nitrogen concentrations (RNC), fine root phosphorus concentrations (RPC), root length (RL), specific root length (SRL), and associated environmental variables were measured. We then tested the relative effects of different assembly processes on taxonomic, functional and phylogenetic diversity using null model and variation partitioning analyses.
Results: Plant taxonomic, functional, and phylogenetic β-diversity all significantly increased with geographic distance, whereas taxonomic and functional β-diversity were more strongly related to geographic distance. Null model analysis revealed that three facets of plant β-diversity exhibited a non-random pattern, indicating niche processes may dominate the gobi desert plant community assembly. Plant functional β-diversity exhibited clustering patterns, while phylogenetic β-diversity displayed dispersion patterns. Among eight traits, only LA and RL demonstrated significant but weak phylogenetic signals, suggesting gobi plant functional traits were not conserved throughout evolution. Variation partitioning analysis further indicated that compared with geographic distance, environmental distance could better explain the variation in all three facets of plant β-diversity. More importantly, local habitat factors, such as soil moisture content and gravel coverage, drove the variation in both three facets of plant β-diversity rather than climatic factors.
Conclusions: These results demonstrated that niche processes, such as habitat filtering, may determine the different facets of plant β-diversity in the gobi desert, and the distribution patterns of plant functional and phylogenetic β-diversity were significantly different. In addition, the mismatch between functional and phylogenetic β-diversity patterns may be partly caused by functional traits that were not conserved along the phylogeny. Taken together, our findings provide new understanding for plant assembly mechanism in extremely harsh environment regime.

Key words: Qinghai-Tibet Plateau, gobi, taxonomic diversity, functional trait, phylogeny, β-diversity