Vegetation restoration alleviates microbial nitrogen limitation in abandoned spoils at early-stage: Implications for vegetation configuration on the Qinghai-Tibetan plateau.

Vegetation restoration in degraded ecosystems is critical for microbial nutrient cycling, which determines recovery effectiveness. The mechanisms plant community configurations regulate microbial metabolism in nutrient-poor substrates remain poorly understood yet, particularly in fragile alpine regions. To examine the capacity of vegetation restoration to alleviate microbial resource limitations in abandoned construction spoil sites at early-stage on the Qinghai-Tibetan Plateau, four vegetation configurations based on Elymus nutans, were designed: bare land (control), monotypic herbs (H), herbs and shrubs combination (SH), and herbs, shrubs and trees combination (TSH).We assessed soil nutrient dynamics, microbial biomass and extracellular enzyme activities (EEAs) by combining eco-enzymatic stoichiometry (EES) and vector analysis. The results revealed that compared to control, vegetation restoration significantly alleviated microbial nutrient limitation, particularly nitrogen limitation, although it significantly reduced soil nitrate (NO₃^-) concentrations by 19-39 %. The underlying mechanisms were: 1) vegetation restoration stimulated microbial metabolism, with C-, N-, and P-acquiring enzymes collectively increasing (e.g., alkaline phosphatase by 3.3-6.2 times) to enhance nutrient mining. 2) microbial communities adjusted their stoichiometric homeostasis. Thus, microbial nitrogen use efficiency (NUE) was increased. Our findings highlight that microbial metabolic plasticity, characterized by enzymatic activation and stoichiometric rebalancing, is pivotal in converting nutrient competition stress into enhanced resource use efficiency. This mechanistic understanding could provide guidelines for vegetation restoration amplify microbial functional resilience in alpine ecosystem.