Improving the enrichment of Cd and Zn in leaf mustard (Brassica juncea) by using metal-activating probiotics

Abstract

Microbial-assisted phytoremediation is of great significance for the remediation of soil contaminated with heavy metals (HMs). Probiotics are beneficial microorganisms that can improve soil structure and fertility and promote plant growth. This study aimed to investigate the effect of two kinds of probiotics, including Lactobacillus casei (L) and Bacillus licheniformis (B), on activating the remediation potentiality of leaf mustard [Brassica juncea (L.) Czerniak.] for mining soil contaminated by Cd and Zn. The results showed that addition of two probiotics significantly reduced soil pH (with 0.05–0.32 units) and improved the available contents of soil HMs (16.0%–59.9% for Cd and 7.1%–23.9% for Zn) in the indoor-incubation experiment. After probiotic treatments, available Cd and Zn in potting soil treated with 1×109 cfu mL-1 of B were 1.65-fold and 1.66-fold of the control, respectively. Meanwhile, soil alkaline phosphatase, urease and sucrose activities were increased, indicating that soil microbial metabolic activities were also motivated. Addition of L and B significantly improved the biomass and chlorophyll contents of leaf mustard. The contents of Cd, Zn in shoot and root were significantly increased with 1×105 cfu mL-1 of L treatment (shoot: 75.2%, 71.9%; root: 36.8%, 61.2%). Furthermore, the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) and the level of malondialdehyde (MDA) were increased or inhibited, indicating that the resistance of plants to HMs was enhanced. These results indicated that two kinds of probiotics could improve the activities of Cd and Zn directly in mining soil and promote the growth of leaf mustard, thus increasing the efficiency of phytoremediation for HMs. The study provides a reference value for probiotic-assisted phytoremediation of soil contaminated with HMs.