Effects of remediation agents on microbial community structure and function in soil aggregates contaminated with heavy metals

• The distribution of available metals varies with different aggregates. • Remediation agents may reduce microbial biomass and bacterial diversity. • Available metals are the main factors modulating bacterial community structure. • The remediation agents increase bacterial function by reducing heavy metal stress. Heavy metal remediation agents have been widely used in contaminated soils, but the remediation effects on heavy metals in soil aggregates and the effects on the structure and function of the microbial communities in aggregates have rarely been reported. Here, sodium silicate, sepiolite, quicklime and monocalcium phosphate were added to soil contaminated with Cu, Zn and Cd. Rice was grown as a test crop. Rice plants and soil samples were then collected after the rice was harvested. The remediation agents decreased the available heavy metal concentrations of both the soil aggregates and rice plants mainly by increasing the soil pH. The changes in bacterial community structure were mainly related to the contents of available heavy metals, and the addition of remediation agents changed the microbial composition. Sodium silicate and sepiolite increased the microbial biomass content in the soil aggregates, while quicklime decreased both microbial biomass and bacterial α-diversity in the soil aggregates. Remediation agents can increase the predicted expression intensity of heavy metal resistance genes and C and N metabolism genes by decreasing the contents of available heavy metals. The influence of heavy metal remediation agents on microbial community structure and function should be considered when selecting heavy metal remediation agents.