Shift of soil bacterial community and decrease of metals bioavailability after immobilization of a multi-metal contaminated acidic soil by inorganic-organic mixed amendments: A field study

A field study was conducted to evaluate the effects of inorganic-organic mixed amendments on metals bioavailability and soil bacterial community structure by Illumina high-throughput sequencing technology. One year after the application of mixed amendments, the pH of the amended soils were 1.99-3.32 unit higher than the non-remediated soil, and the extractable Cd, Pb, Cu and Zn concentrations reduced by an average of 94.54%, respectively. The application of mixed amendments also remarkably improved lettuce (Lactuca sativa L.) growth and inhibited Cd, Pb, Cu and Zn uptake and accumulation in lettuce. The root and shoot Cd, Pb, Cu and Zn decreased by an average of 57.26% and 77.44%, respectively, compared with the control group. In addition, soil respiration and the alpha-diversity of soil bacterial community of the amended soils were significantly increased. With the application of amendments, the relative abundances of Proteobacteria, Bacteroidetes and Actinobacteria decreased, while Acidobacteria and the unclassified bacteria increased. RDA and regression analyses revealed that soil pH, available P and N, and soil extractable Cd, Pb, Cu and Zn concentrations, which were closely related to the application of mixed amendments, were significantly associated with the shift of bacterial community structure. These results prove that the application of mixed amendments not only decreases the bioavailability of heavy metals, but also simultaneously improves soil respiration and soil bacterial diversity. It suggests that a recovery of soil quality seems attainable by application of organic-inorganic mixed amendments.