Biochar and nano-hydroxyapatite combined remediation of soil surrounding tailings area: Multi-metal(loid)s fixation and soybean rhizosphere soil microbial improvement.

The soil near tailings areas is relatively barren and contaminated by multi-metal(loid)s, seriously threatening the safety of crop production. Here, biochar and nano-hydroxyapatite (nHAP) were combined to improve the sterilized and unsterilized polymetallic contaminated soil, and soil incubation and soybean pot experiments were designed. Results showed that biochar and nHAP not only increased soil C, N, and P but also effectively reduced multi-metal bioavailability, wherein the combined application of the two amendments had the best effect on metal immobilization. The synergistic effect of the two amendments decreased the acid-soluble contents of Co, Cu, Fe, and Pb in rhizosphere soils up to 86.75%, 80.69%, 89.09%, and 96.70%, respectively. The ameliorant reduced the accumulation of metal(loid)s in soybean plants, and rhizosphere microorganisms inhibited the migration of soil metals to plants. Additionally, biochar and nHAP regulated the rhizosphere soil microbial community. The rhizosphere soil of the sterilization group tended to prioritize the restoration of the original dominant bacteria. As, Pb, Fe, Urease, OM, TN, and TP were the critical environmental variables affecting rhizosphere soil bacterial communities. Therefore, combining biochar and nHAP is an environmentally friendly strategy to reduce polymetallic mobility in tailings soil and crops and improve soil microbial community structure.

Rhizosphere microbial community composition and survival strategies in oligotrophic and metal(loid) contaminated iron tailings areas.

In this study, the metal(loid) fractions in two alkaline iron tailings areas with similar physico-chemical properties and the enrichment ability of dominant plants in these areas were investigated. Additionally, high-throughput sequencing and metagenome analysis were used to examine the rhizosphere microbial community structures and their strategies and potential for carbon fixation, nitrogen metabolism, and metal(loid) resistance in mining areas. Results showed that Salsola collina, Setaria viridis, and Xanthium sibiricum have strong enrichment capacity for As, and the maximum transport factor for Mn can reach 4.01. The richness and diversity of bacteria were the highest in rhizosphere tailings, and the dominant phyla were Proteobacteria, Actinobacteria, Ascomycota, and Thaumarchaeota. The key taxa present in rhizosphere tailings were generally metal(loid) resistant, especially Sphingomonas, Pseudomonas, Nocardioides, and Microbacterium. The reductive citrate cycle was the main carbon fixation pathway of microorganisms in tailings. Rhizosphere microorganisms have evolved a series of survival strategies and can adapt to oligotrophic and metal(loid) polluted mining environments. The results of this study provide a basis for the potential application of plant-microbial in situ remediation of alkaline tailings.