Grazing enhances soil nutrient effects: Trade‐offs between aboveground and belowground biomass in alpine grasslands of the Tibetan Plateau

Understanding the impact of grazing patterns on grassland production is of fundamental importance for grassland conservation and management. The objective of this study is to obtain an understanding of the trade-offs between aboveground biomass and belowground biomass, which are influenced by environmental factors in free grazing (FG) and grazing exclusion (GE) alpine grasslands on the Tibetan Plateau. We explored the relationships between the trade-off and environmental factors using correlation analysis, a generalized additive model and a structural equation model, and then found that the key factors that determine trade-off showed differences in FG and GE grasslands and that the final structural equation modeling result explained that 96% (path coefficient=0.96) and 65% (path coefficient=0.65) of the variations in the trade-off were due to FG or GE classifications, respectively. The results demonstrated that soil organic carbon, soil carbon/soil nitrogen, and soil available nitrogen affect the trade-off between aboveground and belowground biomass in FG grasslands more obviously than in GE grasslands. However, the effects of growing season temperature on the trade-off were insignificant, -0.218 and -0.181 in FG and GE grasslands, respectively. FG increased the soil bulk density, which resulted in an alteration in the soil pore size distribution and a greater resistance to root penetration. In addition, FG affected the level of soil nutrition, which will affect the nitrogen mineralization of decomposition and absorption, as well as the root biomass. Consequently, this study can provide guidance to improve the quality of grassland.