Edaphic factors control microbial biomass and elemental stoichiometry in alpine meadow soils of the Tibet Plateau

Many meadows are experiencing severe degradation due to the effects of global climate change and other human-related activity, especially overgrazing. The impact of grazing may however vary in different sites, but the dynamics and mechanisms associated with grazing-related meadow degradation on soil microbial biomass structure and function in different locations are still unclear. To address this we examined three alpine meadows with different grazing sites in northwest China, which included grazing in winter and summer, in each of which there were four degradation gradients, varying from no degradation to severe degradation. At the Maqin site, grazing during the summer resulted in higher concentrations of microbial carbon (MBC), nitrogen (MBN), and phosphorus (MBP) compared to grazing during winter. Undegraded meadows (ND) also had higher MBC concentrations compared to low (LD), medium (MD), or severely degraded (SD) ones at the three sites. However, the homeostasis analysis revealed that the elemental stoichiometries were strictly controlled, despite significant degradation-related effects on the concentrations of MBC, MBN, and MBP, indicating relatively stable coupling relationships among C, N, and P. The random forest and partitioning variation analyses showed that edaphic factors play the more important roles in regulating microbial biomass and elemental composition in the different sites. Overall, these results suggest that the effects of degradation on soil microbial biomass concentrations and the stoichiometries are context dependent, particularly with regard to the impact of background soil properties, demonstrating that site conditions must be considered when predicting how grassland ecosystems will respond to grazing-related degradation.