Efficacy of plant growth-promoting rhizobacteria and novel acidified organic amendment to remediate Cd-contaminated soil by Brassica juncea L

Soil heavy metal pollution is a major environmental issue in the world. With ever-increasing industrialization, it is the need of the hour to develop low-cost and eco-friendly heavy metal remediation procedures. Phytoremediation is a new approach to extracting heavy metals from contaminated soil for environmental sustainability. In the present study, Brassica juncea (L.) was tested to extract cadmium (Cd) from contaminated soil using Cd-tolerant plant growth-promoting rhizobacteria (PGPR) and acidified organic amendment. The PGPR were isolated, screened for Cd tolerance, and the best strain (CTB5; Pseudomonas aeruginosa) was selected for seed coating to be used in the pot experiment. To enhance the bioavailability of Cd, elemental sulfur (S^°), molasses, and sulfur-oxidizing bacteria (SOB) were added to the cow dung for acidification. A pot experiment was conducted for 60 days under Cd-spiked and normal soil using Brassica juncea (L.) as test crop with six treatments (T1: Control; T2: 0.5% acidified organic amendment; T3: 1% acidified organic amendment; T4: PGPR-coated seeds of B. juncea; T5: 0.5% acidified organic amendment + PGPR-coated seeds of B. juncea; T6: 1% acidified organic amendment + PGPR-coated seeds of B. juncea). The results have shown that T6 treatment caused a maximum increase in the shoot and root Cd concentration of Brassica juncea (164% and 102%, respectively) over the respective untreated control. Bioconcentration and translocation factors also showed a similar trend. A significant decrease of 34, 52, 41, and 66% in malondialdehyde, peroxidase, superoxide dismutase, and catalase of Brassica juncea was observed due to T6 compared to respective untreated control under Cd-stressed soil. The results suggested that the combined application of PGPR and acidified organic amendment improved the antioxidative defense mechanism of Brassica juncea (L.) and could be employed for effective phytoremediation of Cd-contaminated soil.