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

Abstract

Metalliferous mine tailings have a negative impact on the soil environment near mining areas and render cultivable lands infertile. Phytoremediation involving the synergism of legume and rhizobia provides a useful technique in tackling this issue with cost-effective, environmentally friendly, and easy-to-use features under adverse soil conditions. <i>Leucaena leucocephala</i> has been found to build symbiotic relationships with native rhizobia in the iron-vanadium-titanium oxide (V-Ti magnetite) mine tailing soil. Rhizobia YH1, isolated from the root nodules of <i>L. leucocephala</i>, was classified as <i>Sinorhizobium saheli</i> according to similarity and phylogenetic analyses of 16S rRNA, housekeeping and nitrogen fixation genes. Besides nitrogen fixation, <i>S. saheli</i> YH1 also showed capabilities to produce indole-acetic acid (IAA) (166.77 ± 2.03 mg l^-1) and solubilize phosphate (104.41 ± 7.48 mg l^-1). Pot culture experiments showed that strain YH1 increased the biomass, plant height and root length of <i>L. leucocephala</i> by 67.2, 39.5 and 27.2% respectively. There was also an average increase in plant N (10.0%), P (112.2%) and K (25.0%) contents compared to inoculation-free control. The inoculation of YH1 not only reduced the uptake of all metals by <i>L. leucocephala</i> in the mine tailings, but also resulted in decreased uptake of Cd by up to 79.9% and Mn by up to 67.6% for plants grown in soils contaminated with Cd/Mn. It was concluded that <i>S. saheli</i> YH1 possessed multiple beneficial effects on <i>L. leucocephala</i> grown in metalliferous soils. Our findings highlight the role of <i>S. saheli</i> YH1 in improving plant health of <i>L. leucocephala</i> by reducing metal uptake by plants grown in heavy metal-polluted soils. We also suggest the idea of using <i>L. leucocephala</i>-<i>S. saheli</i> association for phytoremediation and revegetation of V-Ti mine tailings and soils polluted with Cd or Mn.