Soil hydrology affected by crushed rock content modulates the alpine ecological restoration: implications from soil...

Infrastructure construction severely impaired the topsoil that maintains the ecological functions of alpine regions while generating substantial rock by-products that threaten sustainable development. However, in many large-scale infrastructure scenarios, rock by-products and stripped topsoil are separately managed. This study investigated whether soil reconstruction, homogenizing crushed rock with topsoil and subsoil, can simultaneously address waste rock management and hydrology restoration needs. Herein, we conducted a field experiment on the eastern Tibetan Plateau to test the effect of five rock-to-soil ratios (0%, 25%, 50%, 75%, and 100%) and five fine-to-coarse rock mixtures on soil hydrological, nutritional, microbial, and plant responses. Results revealed that 25% and 50% crushed rock contents in soil reconstruction represent important ratios for alpine restoration. Relative to 0% rock-to-soil ratios, the biomass of the plants decreased by 87%-98% when the proportions of rock were 75% and 100%, while it decreased by 1%-20% when the proportions of rock were 25% and 50%. This discrepancy was driven by rock-induced reduction in soil water storage and infiltration, which subsequently constrained microbial biomass and enzyme activities, thereby impairing plant establishment. The 25% crushed rock content emerged as an optional ratio to maintain soil water storage, enzymatic stoichiometry, and plant biomass, achieving levels comparable to those of rock-free controls. Microbial enzymes, particularly those involved in nitrogen metabolism, played an important role in the effectiveness of ecological restoration, as determined by random forest analysis. These findings establish guidelines for soil reconstruction in alpine restoration, enabling sustainable reuse of rocky by-products.