Effects of soil amendments on the ecological restoration of coal fire sites: a case study of Wugong coal fire in Xinjiang, China

Coal fires are major disasters associated with mining that severely damage regional ecosystems. Composite amendments effectively restore coal fire areas ecologically, but their mechanisms for driving the recovery of soil microbial communities remain unclear. Therefore, an orthogonal experimental design for a pot experiment was used to assess soil physicochemical properties, plant photosynthetic parameters, and soil microbial communities to reveal the optimal amendment improvement programs and soil‒microbe‒plant interaction mechanisms for the ecological restoration of coal fire areas. The results demonstrated that the soil organic carbon (SOC) content of the A3B2C1 treatment increased by 300.60%, and the total phosphorus (TP) content of the A3B1C2 treatment increased by 109.09% compared with that of the control (CK). Additionally, compared with those of the CK, the transpiration rate (Tr) increased by 206.62% in the A2B3C1 treatment, the net photosynthetic rate (Pn) increased by 70.62% in the A3B1C2 treatment, and the stomatal conductance (Gs) increased by 244.00% in the A2B3C1 treatment. Among the treatments, the A2B1C3 treatment presented the highest relative abundance of Proteobacteria and Actinobacteriota, whereas the highest relative abundance of Ascomycota occurred in the A3B1C2 treatment. These dominant species were significantly correlated with soil SOC, NH4+‒N and plant TP. Structural equation modeling (SEM) analysis revealed that amendment addition had a significant direct effect on soil nutrients and plant physiological traits but not on soil microbial diversity. The principal component analysis‒affiliation function method revealed that A2B3C1 was the optimal combination of amendments. This study could provide a theoretical basis and technical support for improving soil quality in coal fire areas and constructing green mines.