Abstract: This research was aimed at improvement of the adaptability and performance of plants used for phytoremediation in marginal lands subject to heavy metal contamination, The use of rhizobia to increase biomass productivity is an exciting new development in the phytoremediation of contaminated sites. In the present study, a heavy-metal-tolerant rhizobia strain was isolated from nodules of alfalfa (Medicago sativa) plants grown in copper (Cu) mine tailings in Nanjing. A greenhouse experiment was conducted to evaluate the potential role of this rhizobium strain in encouraging plant growth, Cu uptake and soil remediation by three plant species: M. sativa, Lolium perenne and Sorghum bicolor. The strain of Sinorhizobium meliloti (designated D10) was isolated from root nodules of alfalfa, and was Cu-Pb-Cd-tolerant. Symbiotic association was successfully established between S. meliloti D10 and M. sativa in the current research. It was found that the biomass production of the three species ranked in order: S. bicolor>L. perenne>M. sativa. Inoculation of S. meliloti D10 significantly increased the biomass of M. sativa and S. bicolor, with a 28.6%-78.1% greater biomass for inoculated vs. uninoculated plants. Among the tested plants, S. bicolor accumulated the greatest amounts of Cu. Further, inoculation of S. meliloti D10 resulted in a significant increase in Cu uptake in S. bicolor and M. sativa of 50.4%-111.8% of the uninoculated control. The beneficial impacts of S. meliloti D10 colonization on plant growth and Cu uptake of the three tested species was associated with both improved water-soluble sugar content and increased urease activity. The experiment provided evidence of the potential for use of these plant species in combination with S. meliloti D10 for ecological remediation of metalliferous mine tailings.

Key words: rhizobia, energy plant, copper, marginal lands, soil remediation