Long-term heavy metal contamination altered the structure and function of microbial communities in agricultural soil

Heavy metal (HM) contamination from mining poses a long-term threat to agricultural soils. This study assessed the impacts of long-term HM exposure on soil microbial communities by comparing contaminated and uncontaminated agricultural soils from northwestern China. Using physicochemical analyses and high-throughput amplicon sequencing of bacterial and fungal communities, we assessed impacts on microbial community composition, co-occurrence networks, and predicted functions. HM contamination significantly reduced fungal α-diversity and altered the composition of both bacterial and fungal communities. The relative abundances of Actinobacteria, Acidobacteria, and Chloroflexi increased significantly in contaminated soils. Fungal communities were markedly enriched in Mortierellomycota. Notably, HM contamination substantially reduced the complexity of microbial co-occurrence networks, as indicated by fewer nodes, edges, and keystone taxa. Predictive functional profiling suggested an increased predicted abundance of functions related to HM resistance and detoxification, alongside shifts in core nutrient cycling potentials. Specifically, carbon and nitrogen metabolic pathways were altered, and the proportion of saprotrophic fungi increased, suggesting changes in organic matter decomposition dynamics. In conclusion, long-term HM stress is associated with a shift toward a simplified state, characterized by taxonomic restructuring, less complex co-occurrence networks, and a functional shift toward stress resistance and altered nutrient cycling.