Physiological responses of Morus alba L. in heavy metal(loid)–contaminated soil and its associated improvement of the microbial diversity

Woody plants have considerable application potential in the phytoremediation schemes, owing to their long-lived large biomass and prosperous root systems in heavy metal(loid)–contaminated soil. Under greenhouse conditions, the physiological response characteristics and phytoremediation possibility of Morus alba L. and its associated improvement of the bacterial and arbuscular mycorrhizal fungal (AMF) diversities in heavy metal(loid) co-contaminated soils were investigated. The results showed that the cultivated M. alba L. plant exhibited significant tolerance against the heavy metal(loid)s in co-contaminated soil and that the microbial diversities were improved notably. The contents of malondialdehyde (MDA) in M. alba L. leaves decreased with cultivation from 90 to 270 days, while the superoxide dismutase, peroxidase and catalase activities were maintained at normal levels to eliminate the production of lipid peroxides. The chemical compositions (e.g. amino acids, carbohydrates and proteins) in the root of M. alba L. fluctuated slightly throughout the cultivation period. Meanwhile, Cd, Pb and Zn were majorly concentrated in the M. alba L. roots, and the maximum contents were 23.4, 7.40 and 615.5 mg/kg, respectively. According to the polymerase chain reaction–denaturing gradient gel electrophoresis (PCR-DGGE) analysis results, the influence of M. alba L. on the rhizosphere AMF community was greater than that on the bacteria community. Meanwhile, the bacterial and AMF Shannon diversity indexes in the contaminated soil were enhanced by 18.7–22.0% and 7.14–16.4%, respectively, with the presence of M. alba L. Furthermore, the correlations between the availability of As, Cd, Pb, and Zn and Shannon diversity indexes of the bacterial and AMF communities were significantly (p < 0.05) positive with the phytoremediation of M. alba L. Therefore, M. alba L. can be suggested as a potential plant candidate for ecological remediation and for simultaneously improving the activity and diversity of microorganisms in contaminated soils.