Grazing significantly increases root shoot ratio but decreases soil organic carbon in Qinghai-Tibetan Plateau grasslands: A hierarchical meta-analysis

The Qinghai-Tibetan Plateau (QTP) is the most expansive area of alpine grasslands worldwide, which have been grazed for thousands of years. Distinct environmental conditions render QTP grasslands vulnerable to disturbances. Intensified grazing in the area has led to its degradation in recent decades. However, the effects of grazing on grassland production, soil carbon, and nitrogen contents, their relationships and the factors influencing the grasslands of QTP have yet to be determined. In this study, we evaluated the effect of grazing by using a hierarchical meta-analysis, and explored relation of response variables by structural equation modeling. In all, grazing significantly decreased the aboveground biomass (-38%), total biomass (TB) (-14%), litter (-63%), soil organic carbon (SOC) (-20%), and total nitrogen (TN) (-15%). The root shoot ratio was increased (75%). Grazing intensity exerted significant effects, and mean annual temperature and altitude influenced the responses to a certain degree. Specifically, the response of the root shoot ratio, which can affect the responses of SOC and TN, was significantly higher in the QTP grasslands. Our findings elucidated the response patterns, specialties, relationships, and factors influencing the QTP grasslands, which need to be considered in the development of process-based models and the sustainable use of alpine grasslands on QTP in the future.