Highly cadmium and chromium tolerant rhizosphere bacteria of Albizia julibrissin Durazz on plant growth promoting

Abstract

Using plant growth promoting rhizosphere strains combined with woody legumes is an effective strategy to remediate heavy metals co-contaminated pollution in soil. Despite recent breakthroughs in understanding how rhizosphere strains improve phytoremediation, resources for rhizosphere strain resources with high efficiency to Cadmium (Cd) and Chromium (Cr) resistance are still lacking. Albizia julibrissin Durazz is known as one of the most common leguminous plants. Here, four dominant gram-negative, aerobic strains with nitrogen-fixing ability, phosphate solubilization and indole-3-acetic acid production were isolated from the rhizosphere of A. julibrissin Durazz on Ashby N-free medium. All isolates grew in the presence of 0.1 ~ 100 mg/L Cd and Cr alone or combined stress. Strain ADJ4 exhibited the highest removal efficiency of Cd and Cr alone or combined stress (56.71% ~ 70.86%) and selected isolates for plant inoculation assay. Under Cd and Cr alone or combined stress, ADJ4 inoculation increased seed germination by 1.39% ~ 9.23%, aboveground biomass by 6.11% ~ 70.89% and underground biomass by 36.76% ~ 93.04% while enhancing superoxide dismutase (SOD), peroxidase (POD) and proline (Pro) activities by 10.98% ~ 18.90%, 14.35% ~ 19.74% and 23.05% ~ 48.14%, respectively, relative to non-inoculated controls. Our results underscore the significance of the rhizosphere strains application colonization and efficacy, and plant growth promoting for efficient remediation of Cd-Cr co-contaminated.