Effects and interactions of freeze-thaw leaching on cadmium forms, soil chemical properties, and microbial community...

Heavy metal contamination of soil is one of the major challenges to sustainable agriculture. This contamination can be transmitted through the soil food chain and poses a serious threat to human health. In this study, we found that freeze-thaw leaching (FTL) effectively complements the low removal rate of chemical leaching, and investigated the effects of different numbers of FTL on Cd contamination, soil chemical properties and microbial communities. The results showed that repeated FTL significantly reduced (P < 0.05) the total Cd content in the top soil (19.02 %-49.35 %) and subsoil (0.41 %-21.13 %) and promoted the transformation of Cd to a more stable form, mainly through various removal mechanisms such as complexation, ion-exchange, and chemical precipitation. This finding was supported by reductions in several soil properties, including pH, available potassium (AK), and available phosphorus (AP). FTL treatment initially increased the bioavailability of Cd compared to chemical leaching, but bioavailability of Cd progressively decreased as the number of freeze-thaw cycles increased. Additionally, FTL reduced the richness and diversity of bacteria communities, destabilized ecological symbiotic networks, while increasing the richness and diversity of fungi in the soil. Various model analyses indicated that FTL treatment, available Cd, soil pH, AP and AK were the key drivers influencing the changes in microbial community structure. This study provides new insights and scientific bases for the effective management of heavy metal pollution in agricultural soils, the restoration of ecosystem health, and the improvement of soil sustainability.