Adding mineral-enriched biochar to the rhizosphere reduces heavy metal toxicity on plants and soil microbes

In this study, a mineral-enriched (Ca and P) bagasse biochar was synthesized and characterized. The formulation of Ca and P-enriched bagasse biochar (CPB) was examined for immobilizing arsenic (As), cadmium (Cd), and lead (Pb) in rhizospheric soil. The potential of CPB to alleviate heavy metal stress on plants and soil microbial communities was also investigated. The Ca and P-enriched bagasse biochar demonstrated loading of 88 % Ca and 86 % P with improved pore volume, cation exchange capacity, and water-holding capacity. The FTIR and morphology studies demonstrated an increase in surface functionalities on biochar surface and porous morphology. CPB had 1089±21 µm particle size, 1.1 µm pore size, 0.35±0.01 mv PDI, and 20.8±0.2 mv zeta potential, and displayed no phytotoxicity. The application of the CPB in the soil significantly reduced the availability of As, Cd, and Pb in the soil and their uptake in A. paniculata. CPB application altered the subcellular distribution of As, Cd, and Pb in plant tissues. The CPB spray significantly enhanced the biomass (16–27 %), protein (8–44 %), and chlorophyll (15–61 %) contents of A. paniculata. The application of CPB in metal-contaminated soil resulted in an increased relative abundance of the phylum Proteobacteria and the genera Bacillus, Gemmata, and Sphingobium in the microbial community structure of the rhizospheric soil. The study suggested that CPB formulation can be used as a potential solution to alleviate different metal uptake and toxicity of crops planted in contaminated soil, improve rhizospheric soil quality, and reconstruct the microbial community structure.