Early Revegetation Initiates Soil Physical Habitat Reconstruction and Microbial Community Reassembly Within the First Growing Season in an Alpine Mining Substrate

Ecological restoration of alpine mining areas is constrained by low temperature, infertile substrates, and limited water availability, yet the coordinated early responses of plants, soils, and microorganisms remain poorly understood. We conducted a 90-day in situ revegetation experiment in an alpine sand-and-gravel mine in Tibet using three native perennial grasses, Elymus nutans, Agropyron cristatum, and Festuca sinensis, established in monoculture and mixed-sowing treatments. Plant growth and physiology, soil physicochemical properties, nutrients, enzyme activities, and microbial communities were assessed. All three pioneer species established measurable biomass within the first growing season, although growth and physiological responses differed among planting configurations. Soil capillary porosity, moisture content, and water-holding capacity showed the most consistent improvements, whereas enzyme activities and nutrient responses were more treatment-dependent. Bacterial and fungal communities underwent significant reorganization, while inferred co-occurrence networks showed temporal topological restructuring and sensitivity to simulated targeted node removal. Mantel analysis showed that bacterial community variation was significantly associated with capillary porosity, non-capillary porosity, and total phosphorus, whereas fungal community variation was not significantly associated with the measured soil variables. Overall, 90 days of pioneer revegetation initiated measurable plant–soil–microbial recovery in the alpine mining substrate. Physical and hydrological properties showed clearer early responses than most nutrient indicators, while the observed associations between soil pore characteristics and bacterial community composition suggest a potential link between physical habitat changes and microbial community reassembly.