Soil microbial community responses to the application of a combined amendment in a historical zinc smelting area.

Farmland soils that surround a historical zinc smelting area in northwestern Guizhou, China, are characterized by high levels of heavy metal accumulation. Previous studies have mainly focused on the potential risk evaluations of heavy metals in soil and crops. However, at present, the effects of amendment applications on the bioavailability of heavy metals and on microbial community in the heavily contaminated soils of the mining region are still unclear. A pot experiment was conducted to determine the effect of applying a combined amendment (e.g. lime, sepiolite, and vermicompost) on the diversity and composition of microbial community in the contaminated soil. The results showed that the contents of DTPA- and TCLP-extractable heavy metals (e.g. Cd, Pb, and Zn) decreased and that the pH, SWC, EC, and soil available nutrient (e.g. AN, AP, and AK) contents increased after the application of the combined amendment. Furthermore, application of the combined amendment decreased the diversity of soil bacterial and fungal communities and increased the relative abundances of the dominant bacterial and fungal communities such as Proteobacteria, Bacteroidetes, and Ascomycota; however, the relative abundances of Acidobacteria and Actinobacteria decreased. Redundancy analysis (RDA) and structural equation model (SEM) analysis showed that the bioavailability of heavy metals decreased and that soil physicochemical characteristics improved and had positive or negative effects on the diversity and composition of soil microbial community.