[Remediation of Soil Cadmium Contamination by Solanum nigrum L. Enhanced by the Combination of Exogenous Bacteria and Citric Acid]

To determine how to strengthen the Cd-enriched plant Solanum nigrum L. to remediate cadmium(Cd)-contaminated soil, a pot experiment was conducted with five treatments:control treatment(CK), Glomus mosseae(GM), G. mosseae+citric acid(GM+CA), G. mosseae+Bacillus megaterium(GM+BM), and G. mosseae+B. megaterium+citric acid(GM+BM+CA). We measured soil total Cd, available Cd, plant Cd uptake, and microbial community changes and analyzed the effects of exogenous microbial agents and citric acid addition on the remediation effect of Cd contamination by S. nigrum L. The results showed that relative to that of the CK treatment, the root, stem, and leaf biomass of the GM treatment significantly increased by 35.67%, 41.35%, and 65.38%, and the root and stem biomass of the GM+BM+CA treatment significantly increased by 73.38% and 75.38%. The GM+BM+CA treatment significantly increased Cd accumulation in leaves by 226.84%. The GM+BM+CA treatment significantly increased the Cd transport factor from stem to leaves by 52.47%. The GM+BM+CA treatment significantly increased the leaf bioconcentration factor by 120.53%. In addition, the combined restoration also had an impact on the rhizosphere microbial community structure, especially in inducing the relative abundance of some key microbial groups such as Proteobacteria, Actinobacteria, Glomeromycota, and Olpidiomycota to increase by 2.00%-5.77%, 0.76%-9.96%, 2.11%-3.63%, and 0.54%-2.98%, respectively. According to the RDA analysis, Proteobacteria and Actinobacteria were negatively correlated with soil total Cd, whereas Glomeromycota and Olpidiomycota were negatively correlated with soil total Cd. The changes in key microorganisms enhanced the ability of S. nigrum L. to absorb rhizosphere nutrients and resist Cd stress, increased the Cd accumulation ability of S. nigrum L., and effectively reduced the total Cd content in soil. In conclusion, G. mosseae, citric acid, and B. megaterium activated insoluble Cd in the soil by co-inoculation, which contributed to more Cd accumulation by S. nigrum L. and also produced co-remediation with G. mosseae. The enrichment plant-microorganism combined remediation Cd-contaminated soil has good application potential.