Effects of grazing intensity on the relationship between plant species diversity and primary productivity in an alpine meadow

Grazing has a profound and complex influence on the structure and function of grassland plant communities. In order to explore the influence of long-term different grazing intensities on plant species diversity and productivity in alpine meadow, experimental plots of different grazing intensities were set up in an alpine meadow, and the changes in plant species diversity and productivity and their relationship under different grazing intensities were analyzed. The results showed that with the increase in grazing intensity, both the Shannon-Wiener index and Margalef richness index of the grassland plant community first increased and then decreased. The dominant taxa in the alpine meadow community changed from Gramineae to Cyperaceae and miscellaneous grasses; the dominance of Gramineae decreased from 70% to 12% and that of miscellaneous grasses increased from 13% to 82%. The above-ground net primary productivity (ANPP) of plant communities gradually decreased: by 61.56% under light grazing, by 76.75% under moderate grazing, and by 78.72% under heavy grazing. The under-ground net primary productivity (BNPP) under heavy grazing decreased by 90.06% compared to the corresponding values under grazing prohibition. There was no significant difference in net primary productivity (NPP) between light grazing, moderate grazing, and grazing prohibition. The NPP of the three treatments remained stable as a whole. The results indicate that increased intensity of grazing leads to a decrease in plant height, while moderate grazing increases the tillering number of Cyperaceae plants. The Pielou index of the alpine meadow plant community was negatively correlated with NPP, whereas the Margalef index was positively correlated with BNPP. Moderate grazing intensity is beneficial for maintaining high species diversity in alpine meadows, while heavy grazing is detrimental to maintaining high species diversity and grassland productivity in alpine meadows.