Soil ecological stoichiometry reveals microbial nutrient limitation with alpine meadow degradation in northeastern Tibetan Plateau

Alpine meadow degradation results in an imbalance of soil nutrient supply, with soil microorganisms playing a pivotal role as regulators of soil nutrient cycling. However, the metabolic limitations of soil microorganisms during the process of alpine meadow degradation have not been adequately elucidated. The objective of this study was to uncover the characteristics and driving factors underlying the metabolic limitations imposed on soil microorganisms during alpine meadow degradation. Here, we assessed the levels of total and available nutrients in soil, as well as microbial biomass and extracellular enzyme activities (including cellobiosidase [CBH], beta-1,4glucosidase [BG], beta-1,4-N-acetylglucosaminidase [NAG], L-leucine aminopeptidase [LAP], and alkaline phosphatase [AP]) in degraded alpine meadows located on the northeastern Tibetan Plateau. The results demonstrated that alpine meadow degradation led to a reduction in soil C, N, and P contents, as well as available nutrients, microbial biomass, and soil extracellular enzyme activities. Analysis using the vector-threshold element ratio (VT) model revealed an increasing trend in microbial C limitation with the progression of alpine meadow degradation. In the 0-20 cm soil layer, microbial N limitation gradually weakened and shifted towards P limitation; however, an opposite pattern was observed in the 20-40 cm soil layer with worsening alpine meadow degradation. Additionally, alpine meadow degradation enhanced the microbial carbon use efficiency (CUE), which was negatively correlated with microbial C limitation but was positively correlated with N & P limitations. Moreover, there was a weakening of soil microbial homeostasis associated with increased alpine meadow degradation levels, where available nutrients played a crucial role in driving nutrient limitations for soil microbes in degraded alpine meadows. The findings of this study contribute to enhancing the understanding of the key factors governing soil microbial nutrient limitation in degraded alpine meadows, thereby providing valuable theoretical support for improving soil quality and health in such alpine meadow ecosystems on the Qinghai-Tibetan Plateau.