Enhanced Phytoextraction of Heavy Metals from Contaminated Soil by Plant Co-cropping Associated with PGPR

In this study, 1-year greenhouse pot experiments were conducted to investigate the effect of Phyllobacterium myrsinacearum strain RC6b on the growth and phytoextraction efficiency of heavy metals by a Zn/Cd hyperaccumulator (Sedum alfredii) and alfalfa (Medicago sativa L.) in a co-cropping system. The treated soil sample was collected from a land reclamation site of Pb/Zn mine tailings in Hanzhong City, Shaanxi Province, China. Results showed that, with the inoculation of RC6b, shoot biomass yields of plants were significantly increased by 15.9-20.2 % and 17.2-19.9% for alfalfa and S. alfredii, respectively, compared to the non-inoculated plants. Biomass yield of alfalfa was higher than that of S. alfredii. RC6b inoculation increased metal concentrations by 18.6-31.2 % (Pb), 23.8-37.5 % (Cd), and 26.4-38.3 % (Zn) in S. alfredii shoots, and by 13.8-24.7 % (Pb), 15.8-26.6 % (Cd), and 24.8-35.6 % (Zn) in alfalfa shoots, respectively. After six consecutive harvests of shoots, RC6b inoculation increased the phytoextraction efficiencies of Pb, Cd, and Zn by shoots of the co-planting system by 16.9, 46.3, and 60.9 %, respectively. Nevertheless, phytoextraction of Cu was not improved by RC6b inoculation. In the co-planting/inoculation system, the percentage removals of metals from soil by the plant shoots were 6.09, 30.97, 11.10, and 1.68 % for Pb, Cd, Zn, and Cu, respectively, after six harvests of shoots. Inoculation with RC6b significantly increased the soil microbial activity and the carbon utilization ability of the soil microbial community.