Synergistic enhancement of soil multifunctionality by biochar and arbuscular mycorrhizal fungi via improved nutrient supply in coal mining reclaimed soils

Coal mining activities cause the destruction of surface vegetation, degradation of the soil structure, and severe loss of organic matter, thereby reducing soil multifunctionality. Biochar (BIO) and arbuscular mycorrhizal fungi (AMF) play crucial roles in mediating soil quality and crop production, especially in resource-constrained poor soils. However, little research has documented the synergistic effects of BIO + AMF on soil multifunctionality in coal-mine reclamation areas. Here, a three-year field investigation was carried out to evaluate the effects of four treatments: CK (traditional planting, no AMF and no BIO), AMF (AMF without biochar), BIO (biochar without AMF), and BIO + AMF (biochar and AMF). The findings demonstrated that the BIO + AMF treatment significantly modified the soil physical structure, increasing the soil water retention while decreasing the soil bulk density. The application of biochar supplemented with AMF notably increased the soil enzyme activity, nutrient supply, and the alpha and beta diversities of the soil bacterial and fungal communities. Moreover, biochar and AMF synergistically enhanced soil multifunctionality, and a random forest model revealed that the combination of AMF inoculation and biochar application increased maize production, which was driven mainly by soil enzyme activity, and that soil multifunctionality was regulated mainly by the nutrient supply function. These results highlight that biochar combined with AMF inoculation had significant synergistic effects on improving maize productivity and multifunctionality, providing a nature-based restoration strategy for use in reclaimed soil.