Abstract:

Aims: During the first two decades of the 21st century, China has made remarkable progress in desertification control. The area of desertified and degraded grassland has been decreasing and the amount of vegetation has been increasing. However, it remains unclear how plant diversity varies during vegetation restoration. This knowledge gap hinders a full assessment of the effectiveness of desertification control efforts. Our goal was to quantify species diversity, functional diversity, and phylogenetic diversity in plant communities at different phases of vegetation restoration (semi-fixed dunes, fixed dunes, fixed dunes covered with biological soil crusts, fixed dunes with abundant herbaceous plants) in the Mu Us sandy grassland.

Methods: We conducted field investigations and leaf trait measurements (leaf thickness, leaf dry matter content, leaf density, and specific leaf area) during the mid-growing season of 2020 in Yanchi, Ningxia. Based on this, we further used one-way ANOVA and Pearson correlation analysis to explore the differences and relationships among diversity indices at different phases of vegetation restoration.

Results: Our results indicated that: (1) Most leaf traits exhibited no significant phylogenetic signal, implying that leaf functional traits were primarily driven by environmental factors. (2) For α-diversity, Shannon-Wiener diversity (H), species richness (S), functional richness (FRic), and phylogenetic diversity (PD) were the lowest in plant communities at the phase of fixed dunes covered with biological soil crusts. Each of these α-diversity parameters were not significantly different among plant communities during the other three restoration phases. Furthermore, these biodiversity indices were positively correlated with each other, suggesting coordinated changes in species diversity, functional diversity, and phylogenetic diversity during vegetation restoration. (3) All β-diversity indices increased with the number of transitions between phases, indicating that species composition, leaf traits, and phylogeny were consistently changing during vegetation restoration. Species composition, leaf traits, and phylogeny all changed dramatically during the transition from semi-fixed to fixed dunes, resulting in a large dissimilarity between communities during the two phases. (4) The phylogenetic structure of plant communities tended to diverge on fixed dunes, fixed dunes covered with biological soil crusts, and fixed dunes with abundant herbaceous plants, indicating that competitive exclusion was the key factor driving community organization. However, the phylogenetic structure of plant communities on semi-fixed dunes did not exhibit any consistent patterns, implying that community organization was affected by the combined effects of habitat filtering and competitive exclusion.

Conclusion: Although plant diversity did not demonstrate a monotonic increasing trend during vegetation restoration in the Mu Us sandy grassland, different indices of diversity varied coordinately. Therefore, species diversity can be regarded as a reasonable proxy of functional and phylogenetic diversity in this system. The results of this study can provide reference for vegetation construction and management whilst implementing desertification controls, as well as provide scientific basis for the ecological conservation and biodiversity protection of the Mu Us sandy grassland.

Key words: species diversity, functional diversity, phylogenetic diversity, vegetation restoration, the Mu Us sandy grassland