Objective In the mining areas of open-pit coal mines in the arid and semi-arid regions in western China, water scarcity severely restricts ecological restoration. As preliminary ecological effects have been achieved through soil layer reconstruction and bioremediation-based reclamation technologies in waste dumps of the mining areas, there is an urgent need to investigate the effects of both technologies on the water use and growth of representative plants. This will provide a scientific basis for accelerating ecological restoration in the mining areas.

Methods In a waste dump of the Heidaigou open-pit coal mine in Inner Mongolia, four experimental program for soil layer treatment were conducted, i.e., three-layer structured soils with no fungal inoculation (C-CK), three-layer structured soils with Arbuscular mycorrhizal fungi (AMF) inoculation (C-AM), mixed soils with AMF inoculation (D-AM), mixed soils with no fungal inoculation (D-CK), with Amorpha fruticosa used as the test plant. Using in situ field experiments on soil water evaporation and infiltration, combined with hydrogen and oxygen isotope analysis of water, this study investigated water distribution in reconstructed soil layers combined with bioremediation-based reclamation and explored the effects of the combination on plant water use. Besides, the primary factors influencing the water use efficiency (WUE) and plant height were identified using variance analysis and principal component analysis.

Results and Conclusions In the waste dump, three-layer structured soils effectively reduced soil water evaporation, and the underlying impermeable layer prevented water leakage, thereby achieving water retention. Specifically, the overall water storage of the three-layer structured soils in the C-CK and C-AM zones proved 9.1% and 8.37% higher than that of the mixed soils, respectively. After reclamation, AMF inoculation accelerated water infiltration, reduced evaporation, and increased the water consumption of Amorpha fruticosa. Furthermore, AMF inoculation enhanced the WUE of Amorpha fruticosa by promoting root development and photosynthesis, with the WUE of the C-AM treatment measuring 1.18, 1.40, and 2.30 times that of the C-CK, D-AM, and D-CK treatments, respectively. The growth indicators of Amorpha fruticosa under the four treatments decreased in the order of C-AM, D-AM, C-CK, and D-CK. The three-layer structure of soils enables the effective retention of soil moisture. This structure, combined with AMF inoculation, can promote the root development and photosynthetic rate of Amorpha fruticosa, thus enhancing its WUE under limited water resources. The reclamation technology integrating three-layer structured soil and AMF inoculation can serve as an ecological reclamation measure for the waste dumps of open-pit coal mines in western China, thereby contributing to the sustainable development of green mines.