Optimized bio-fertilization drives the synergistic recovery of vegetation productivity and soil multifunctionality by reshaping fungal interaction patterns in degraded alpine mines

Restoring degraded alpine mining ecosystems is critically constrained by soil infertility and the functional decoupling of plant–soil–microbe interactions. While optimized bio-fertilization represents a promising restoration strategy, the mechanisms linking vegetation recovery, shifts in fungal community structure, and soil multifunctionality (SMF) remain poorly understood. We conducted a three-year field restoration experiment at the Muli coal mine on the Qinghai–Tibet Plateau to evaluate the integrated responses of plant communities and soil functional networks to various fertilization regimes. The optimized regime (W3J1, comprising 375 kg·hm⁻ 2 of forage-specific fertilizer and 350 kg·hm⁻ 2 of microbial inoculant) elicited the most robust ecological recovery. By the end of the 2024 growing season, it increased absolute vegetation coverage to 77.31% and enhanced aboveground biomass to a peak of 352.67 g·m⁻ 2 . Concurrently, the SMF index in W3J1 reached a peak of 0.95, effectively reversing the functional impairment observed in the degraded control (CK). Furthermore, co-occurrence network analysis revealed enhanced fungal community complexity, with the W3J1 treatment expanding network connectivity to 900 edges (compared to 728 edges in the CK), while the W1J3 treatment achieved the highest OTU richness (693). Notably, excessive nutrient inputs in the W3J3 treatment failed to yield additional benefits, as SMF and fungal diversity indices stabilized or declined due to resource imbalances. Random Forest modeling identified vegetation density as the paramount predictor of fungal diversity. Structural Equation Modeling (SEM, R 2 = 0.67) further elucidated a cascading pathway where fertilization directly promoted fungal diversity (standardized path coefficient β = 0.76) and initiated vegetation establishment, which subsequently facilitated shifts in the fungal community structure and interaction networks. The optimized co-application of microbial agents and fertilizers facilitates ecosystem reconstruction by orchestrating the coupling between vegetation density and fungal stability. This provides a theoretical basis for the sustainable restoration of severely degraded alpine mines.