The synergetic effect of biochar (BC) and plant growth promoting bacteria (PGPB) on phytoremediation potential of plants in heavy metal (HM) contaminated soils was not well understood. A pot experiment was carried out to evaluate the effects of banana pith derived BC (0, 2.5 and 5%, w/w) as soil amendment together with inoculation of PGPB Bacillus thuringiensis SE1C2 on the growth, physiological response and phytoremediation potential of Sorghum bicolor (L.) Moench in Cd and Zn contaminated soils. Combined treatment of BC 5% and SE1C2 increased plant shoot length, root length, fresh weight and dry weight but decreased Cd and Zn accumulation as compared to other treatments. The BC 5% treatment also increased SE1C2 colonization in rhizosphere soils and tissue interior of S. bicolor even under HM stress. In addition, the plants treated with BC 5% and SE1C2 also had increased chlorophyll, carotenoid and antioxidant enzymes while lower leaf malondialdehyde and proline contents which suggest their potential in improving HM stress tolerance in plants. Similarly, the combined BC 5% and SE1C2 treatment considerably improved enzymatic activities (acid phosphatases, alkaline phosphatases, beta-glucosidase and urease) in HM contaminated soils. Thus, this study concludes that the combined treatment of Bacillus thuringiensis SE1C2 and banana pith BC could be exploited as an effective strategy for improving the plant growth and phytostabilization potential in HM contaminated soils.
