Assessment of bacterial communities in Cu-contaminated soil immobilized by a one-time application of micro-/nano-hydroxyapatite and phytoremediation for 3 years.

Heavy metals contamination of soil has been considered as a global environmental problem, and consequently various soil amendments have been widely used in immobilization. Previous studies have reported that micro-/nano-hydroxyapatite (MHA/NHA) as a novel chemical material could alleviate soil acidity and reduce the bioavailability of heavy metals. However, the mechanism of soil microorganism responding to the application of MHA/NHA is little studied. Presently, an in-situ field experiment was conducted to determine the effects of MHA/NHA and the other three traditional amendments including alkali slag (AS), lime (L) and apatite (AP) on soil copper (Cu) bioavailability and dominate bacterial population. The results showed that the application of MHA/NHA effectively increased soil pH and decreased soil available Cu content, and showed the highest increasing effects on the activities of urease, catalase and acid phosphatase. Compared with the control, MHA/NHA significantly changed the soil bacterial community structure and increased the bacterial abundance and diversity. Besides, analysis of the dominate population showed that the application of MHA/NHA decreased the relative abundance of acidophiles and the indicator of soil degradation. Additionally, the relative abundance of potential plant growth promoting bacteria increased with the addition of MHA/NHA, which was confirmed by the characteristics (the ability of producing indole acetic acid and siderophore) of bacterial strains. These results suggested that these dominate bacterial populations with significant changes may be regarded as the biomarkers for the recovery of soil ecological environment, which provides a theoretical basis for the ecological evaluation of MHA/NHA.