Grazing altered the plant diversity-productivity relationship in the Jianghan plain of the Yangtze River basin

Purpose: The Jianghan Plain is located in the middle reaches of the Yangtze River, characterized by high precipitation, flat terrain, and high vegetation cover. Livestock grazing is one of the major agricultural activities. Heavy grazing in some areas causes soil erosion and ecosystem degradation. We aim to quantify the effects of grazing of various grazing intensities on plant diversity and productivity as well as on soil nutrient dynamics in the area. Methods: To examine the effects of grazing on plant diversity and productivity as well as on soil nutrient dynamics, we measured and compared the above-ground biomass (AGB), species composition (alpha and beta diversity indices), soil total phosphorus (STP), soil total nitrogen (STN), and soil organic carbon (SOC) under three grazing intensity levels: light grazing (LG), moderate grazing (MG) and heavy grazing (HG).Results: The results show that grazing intensity levels affected plant diversity, productivity, and soil nutrient dynamics differently. Species turnover refers to the rate of species substitution in different communities. The turnover dissimilarity value of species was 0.233 between LG and HG and 0.313 between LG and HG. AGB, STP, STN, Shannon-Wiener index, and plant productivity were all decreased under HG. In contrast, plant diversity (the Berger-Parker index) increased under HG. The relationships between plant diversity and productivity were also affected by grazing intensity. Under LG and MG, plant diversity was positively correlated with productivity, but became negative under HG.Conclusions: HG reduced plant diversity and altered the relationship between plant diversity and productivity, which caused ecosystem degradation. Thus, grazing management should aim to control the intensity of grazing at light to moderate levels to ensure the long-term sustainability of the ecosystem.