Synergistic Restoration Mechanisms of Degraded Alpine Grasslands Using Microbial Inoculants and Organic Fertilizers

This project addresses the secondary degradation of perennial sown grasslands on the Qinghai-Tibet Plateau caused by sluggish nutrient turnover. Through a two-year in situ field experiment, we evaluated the synergistic effects of combining a uniform basal organic fertilizer (3000 kg/ha) with varying dosages of microbial inoculants (25-100 kg/ha). The findings identified 75 kg/ha of microbial inoculant as the optimal dosage for ecological restoration. This optimized treatment significantly boosted aboveground biomass by 94% in 2024 and 96% in 2025 compared to unfertilized controls. Furthermore, it elevated the soil multifunctionality (SMF) index by 87% to 122% relative to sole organic fertilization, aligning with peak extracellular enzyme activities. Network analysis revealed that this specific dosage doubled fungal network connectivity and enriched indigenous keystone taxa, such as Mortierella, through a short-term priming effect. Piecewise structural equation modeling uncovered a cascaded regulatory pathway: the expansion of soil nutrient pools stimulates extracellular enzyme activities, which subsequently drive SMF enhancement. Within this framework, microbial communities sustain soil functioning by mediating network restructuring rather than acting as direct drivers. Ultimately, integrating 3000 kg/ha organic fertilizer with 75 kg/ha microbial inoculant offers a scientifically robust strategy for the sustainable management of alpine grasslands, though high-dosage regimes warrant long-term monitoring for potential pathogen accumulation.