Differences in plant community and soil of alpine meadow under different grazing patterns on the Qinghai–Tibet Plateau

Although different grazing management regimes have different effects on plant communities and soil in grasslands, little is known regarding the effects of different grazing patterns on plant communities and soils in alpine meadows. In this study, we sought to examine the differences in plant community and physical and chemical properties of soil in alpine meadows under winter grazing (WG), summer grazing (SG), and year-round grazing (AG) in Hongyuan County, Sichuan Province, in the northeastern part of the Qinghai–Tibet Plateau. We found that plant community coverage and number of species under AG were significantly lower than those in meadows subjected to WG and SG (P < 0.05). In addition, the community height, above- and belowground biomass under AG and SG were significantly lower than those under WG (P < 0.05). However, the proportion of unpalatable forbs showed the opposite pattern. There were, however, no significant differences with respect to root: shoot ratio among the three treatments (P > 0.05). The dominant plants were significantly different under the three grazing management regimes, with those in meadows under AG being species in the families Compositae and Ranunculaceae. The dominant plants under WG were Gramineae, Ranunculaceae, and Sedge, whereas those in meadows under SG were from Compositae and Gramineae. There was no significant difference in soil pH at depths of between 0 and 20 cm in meadows under AG and WG (P > 0.05), although the values were both significantly higher than that under SG (P < 0.05). Furthermore, there were no significant differences in pH between soil at depths of 0 – 10 cm and 10 – 20 cm (P > 0.05). The contents of NH₄⁺-N, NO₃⁻-N, available phosphorus, and total nitrogen in soil were all higher in WS and SG than in AG, whereas the contents of soil total phosphorus showed no significant differences in meadows under AG and SG (P > 0.05), both of which were, however, lower than that in WG. With regards to soil depth, all assessed soil contents were significantly higher in the surface soil (0 – 10 cm) than in deeper soil (10 – 20 cm) (P < 0.05). The findings of this study revealed that, compared with seasonal grazing (WG and SG), year-round grazing reduced plant community height, coverage, biomass, litter, and the number of species, and altered the proportion of forage, thus reducing the stability of alpine meadow plant communities and resulting in pronounced soil nutrient loss and reduced fertility. Accordingly, we suggest that seasonal grazing can contribute to stabilizing meadow plant communities, and ensure the maintenance of community productivity and stability. This is in turn will be conducive to the sustainable development of alpine meadow pastures on the eastern Qinghai–Tibet Plateau.