Crop Cultivation Reshapes Soil Microbiomes to Drive Heavy Metal Mobilization in Restored Mining Areas

Mining activities cause substantial heavy metal release. Ecosystem restoration is considered one of the most effective ways to prevent heavy metal mobilization in mining areas. Previous studies have suggested that microorganisms play crucial roles in heavy metal transport in heavy metal-contaminated farmland soils. However, the interactions between the geochemical fractions of heavy metals and microbial communities under crop cultivation in restored mining areas are still unclear. In this study, we systematically collected farmland soil (FS) and grassland soil (GS) from a restored mining area to reveal the effects of crop cultivation on the composition of soil microbiomes and their potential roles in heavy metal mobilization. The results revealed that the exchangeable fractions of heavy metals (Cd, Zn, and As) in FS (11%, 11%, and 1.3% on average, respectively) were significantly greater than those in GS (30%, 19%, and 3.2% on average, respectively), indicating that agricultural activities promoted heavy metal mobilization in restored mining areas. In addition, we determined that microbial attributes, including microbial diversity, composition, and community structure, were significantly different in FS and GS. Furthermore, our results revealed that such differences were driven mainly by heavy metals and their exchangeable fractions in soils. Notably, the dominant genera enriched in FS were extensively involved in heavy metal mobilization, which is consistent with the fact that heavy metal metabolism-related genes were enriched in FS. Taken together, our findings suggest that soil microorganisms play an important role in heavy metal mobilization under crop cultivation in restored mining areas.