Effects of different grazing methods on the composition and structure of plant functional groups in grassland community

  Objective  Plant functional groups (PFGs) and their diversity are crucial for maintaining the complexity and stability of communities. This study analyzed the composition and structure of PFGs under different grazing regimes, with the objectives to reveal the mechanisms underlying the assembly, distribution and adaptation of plant communities, and to provide insights into the prediction of community succession and sustainable management of grasslands.

  Method  We conducted a community survey (species, plant number, height, density and biomass) under different grazing regimes (no grazing, seasonal grazing and continuous grazing) in the Chen Barag Banner, Hulunbuir, Inner Mongolia of northern China, and then analyzed the summed dominance ratio (SDR₄) of PFGs based on life forms and ecotypes.

  Result  A total of 35 plant species were recorded, belonging to 11 families, 5 life forms, and 3 water ecotypes, among which, Compositae had the most species, accounting for 25.7% of total abundance, followed by Gramineae, accounting for 20% of total abundance. The importance value of Carex duriuscula was the highest under continuous grazing, while Leymus chinensis was the most dominant species in no-grazing sample plots. Both Margalef richness index and Shannon-Wiener index were significantly higher in the seasonal-grazing sample plots than in continuous grazing and no-grazing sample plots. With regards to different life forms, annuals and biennials showed significantly higher SDR₄ in continuous-grazing sample plot than in seasonal-grazing and no-grazing sample plots, whereas perennial bunch grasses showed relatively low SDR₄ in continuous-grazing sample plots. With regard to ecotypes, most species were xerophytes, whose SDR₄ increased with grazing intensity. In contrast, the SDR₄ of mesophytes decreased with increasing grazing intensity.

  Conclusion  In the grassland community of the study area, the species of perennial rooting stem grass functional groups are mesophytes, while the species of primary and biennial herb functional groups are mostly xerophytes. Compared with long-term grazing prohibition, rest grazing significantly improves the species diversity of grassland community, and promotes the functional groups of perennial grasses and mesophytes to gradually replace the functional groups of primary and biennial herbs and xerophytes. Therefore, the scientific rest grazing system is conducive to the protection of grassland plant diversity and the restoration of degraded ecosystem.