Amended engineered soil promotes coordinated soil-plant-microbiome responses during early-stage slope restoration.

Amended Engineered Soil (AES), a functional substrate incorporating biomass-derived straw fiber, has been applied for the ecological restoration of degraded slopes. However, how AES affects the coordinated responses of substrate structure, root development, and rhizosphere microbiome assembly during early-stage restoration remains unclear. In this study, AES and Conventional Engineered Soil (CES) were compared during a 90-day slope restoration experiment using Lolium perenne as the target species. Compared with CES, AES substantially improved substrate moisture and nutrient conditions, with water content increasing from approximately 10.4%-16.6% and available phosphorus increasing more than fivefold. AES also promoted the formation of large water-stable aggregates, indicating improved structural stability of the reconstructed substrate. These changes were accompanied by marked improvements in vegetation establishment, including a 18.4% increase in plant height, more than 40% increase in dry biomass, and a pronounced increase in root length. Root tensile strength was also enhanced, suggesting greater belowground reinforcement. AES significantly increased bacterial richness and Shannon diversity, whereas the fungal response was mainly reflected in increased richness rather than diversity. Correlation analysis further showed close associations among substrate nutrient conditions, plant growth, root reinforcement, and microbial diversity. These findings suggest that AES promotes early-stage slope restoration through the coordinated improvement of substrate quality, vegetation establishment, root development, and rhizosphere microbial communities, while providing a sustainable pathway for biomass resource utilization.