Interaction of Cd-hyperaccumulator Solanum nigrum L. and functional endophyte Pseudomonas sp. Lk9 on soil heavy metals uptake

Bioaugmentation is a promising method for assisting phytoextraction of heavy metals from contaminated soil, and the development of bioaugmentation-assisted phytoextraction requires the understanding of the mechanism involved in the interaction between plants and inocula. In this study, a pot study was conducted to evaluate the effect of bacterial endophyte Pseudomonas sp. Lk9 which can produce biosurfactants, siderophores and organic acids on the growth and metal uptake of Cd-hyperaccumulator Solanum nigrum L. growing in multi-metal-contaminated soil. The results revealed that Lk9 inoculation could improve soil Fe and P mineral nutrition supplies, enhance soil heavy metal availability, and affect host-mediated low-molecular-weight organic acids secretion, thereby significantly increasing S. nigrum shoot dry biomass by 14% and the total of Cd by 46.6%, Zn by 16.4% and Cu by 16.0% accumulated in aerial parts, compared to those of non-inoculated control. The assessment of phytoextraction showed that Lk9 inoculation elevated the bioaccumulation factor of Cd (28.9%) and phytoextraction rates of all metals (17.4%, 48.6% and 104.6% for Cd, Zn and Cu, respectively), while the translocation factors had negligible difference between Lk9 inoculation (3.30, 0.50 and 0.40 for Cd, Zn and Cu, respectively) and non-inoculated control (2.95, 0.53 and 0.42 for Cd, Zn and Cu, respectively). It was also found that the symbiotic association between S. nigrum and Lk9 significantly increased the soil microbial biomass C by 39.2% and acid phosphatase activity by 28.6% compared to those in S. nigrum without Lk9. This study would provide a new insight into the bioaugmentation-assisted phytoextraction of heavy metal-contaminated soils.