Effect of plant growth-promoting rhizobacteria on oilseed rape Brassica juncea and phytoextraction of cadmium

PurposeThere is an urgent need to remediate heavy metal-contaminated soils. However, the role of plant growth-promoting rhizobacteria (PGPR) in phytoextraction of heavy metals is far from being well understood. This study aimed to examine the effect of two newly isolated PGPRs on oilseed rape Brassica juncea to extract cadmium (Cd) from contaminated soils and reveal possible underlying mechanisms of PGPR-assisted Cd phytoextraction.MethodsTwo Cd-resistant PGPRs, Bacillus sp. Kz5 and Enterobacter sp. Kz15, were isolated from the rhizosphere of plants grown in copper-mine soils. Seeds of oilseed rape B. juncea were treated with Kz5 and Kz15 suspension, transplanted into soils, and grown in greenhouse pots for 3 weeks. Plant biomass, Cd concentrations, root morphological parameters, photosynthetic parameters, and rhizosphere soil properties were analyzed. Pearson's correlation coefficient (PCC) analysis and principal component analysis (PCA) were conducted to examine the relationships among plant biomass, Cd concentrations, and the parameters.ResultsThe inoculation of the Kz5 and Kz15 significantly increased the plant biomass and Cd concentrations compared to those without PGPR inoculation (p < 0.05). In addition, the root morphology, photosynthetic activity, and rhizosphere soil properties were improved with the inoculation of the PGPRs. There are significant positive correlations between Cd concentrations and plant development indicators.ConclusionSignificant effects of PGPRs on plant growth promotion and Cd phytoextraction were observed. Such effects were associated with the improvement of plant root morphology, photosynthetic activity, and rhizosphere soil properties. This study provides PGPRs for assisted phytoextraction as a potential strategy to remediate Cd-contaminated soil.