Shrub Encroachment Rewires Microbial Networks to Suppress Soil Organic Carbon Mineralization in Subalpine Meadows

Subalpine meadow ecosystems have undergone widespread shrubification over the past century due to climate change and anthropogenic activities, yet the impacts on soil organic carbon (SOC) mineralization and temperature sensitivity (Q₁₀) remain unclear. We carried out laboratory incubation experiments with soils from native subalpine meadows and shrub-encroached areas on Luliang Mountain. Soil properties, organic carbon fractions, and microbial communities were analyzed to assess their roles in SOC mineralization and Q₁₀. The results showed that shrubification acidified soils, increased nutrients, reduced labile carbon (dissolved organic carbon, DOC), and elevated stable carbon (mineral-associated organic carbon, MAOC). It raised microbial α-diversity but reduced network complexity, with fungi responding more strongly. SOC mineralization rates decreased across depths due to lower pH, higher stable carbon, and disrupted microbial interactions. Total mineralization and Q₁₀ in surface soil (0-5 cm) were notably reduced. Structural equation modeling indicated that in meadows, pH and nutrients co-regulated mineralization, while under shrubification, nutrients dominated, altering microbial networks (weakening Pseudomonadota, Actinomycetota, Acidobacteriota, Ascomycota, and Basidiomycota interactions) to suppress SOC mineralization. These findings highlight that shrubification reshapes the key mechanisms of carbon mineralization, with soil nutrients playing a complex regulatory role in carbon dynamics. Our results from this typical subalpine region provide insights for predicting SOC mineralization feedbacks to climate change and understanding shrubification impacts on regional carbon balance.