Inoculation of Sinorhizobium saheli YH1 Leads to Reduced Metal Uptake for Leucaena leucocephala Grown in Mine Tailings and Metal-Polluted Soils

Multi-metalliferous accumulation of mine tailings shows a negative impact on the soil environment dedicated to mining industry, rendering cultivable lands infertile. Phytoremediation involving the synergism of legume and rhizobia provides an effective technique in tackling this issue with cost-effective, environmentally friendly, and easy-to-use features under adverse soil conditions. Leucaena leucocephala built symbiotic relationship with native rhizobia in the iron-vanadium-titanium oxide (V-Ti magnetite) mine tailing soil. A symbiotic rhizobia YH1 isolated from the root nodules was classified as Sinorhizobium saheli according to similarity and phylogenetic analysis of 16S rRNA, housekeeping and nitrogen fixation genes. Beside nitrogen fixation, S. saheli YH1 showed capability of indoleacetic acid (IAA) secreting and phosphate solubilization. S. saheli YH1 increased the biomass and contents of nitrogen, phosphorus and potassium for L. leucocephala, but decreased metal uptake in the Cd- and Mn-contaminated soil and V–Ti magnetite mine tailings, suggesting S. saheli YH1 showed multiple beneficial effects on L. leucocephala growth in the metalliferous soil. Our findings underline the role of symbiotic rhizobia in improving tolerance legume plants to single- or multi-metals and emphasize the potential of using L. leucocephala and S.saheli symbiosis for revegetation of V-Ti mine tailings and soils polluted with Cd and Mn.