Influence of iron-enriched biochar on Cd sorption, its ionic concentration and redox regulation of radish under cadmium toxicity

Cadmium (Cd), a potent heavy metal, causes a significant reduction in plant growth and its yield by interfering with the plant's mineral nutrition and, primarily, by inducing Cd-induced oxidative damage. Cd mobilization at the soil-root interface is also very important in context of its bioavailability to plants. Therefore, an experiment was carried out to evaluate the mitigating role of iron-enriched biochar (Fe-BC) on Cd accumulation in soil and Cd toxicity in radish plants. Radish seeds were sown in pots, and two levels of Cd (0 and 0.75 mg kg-1) and two levels of Fe-BC (0 and 0.5%) were applied. Cd stress significantly reduced radish fresh and dry biomass production, which was due to high production of malondialdehyde (36%) and increase in cell membrane permeability (twofold) relative to control. Moreover, Cd stress considerably reduced chlorophyll concentrations and uptake of some essential nutrients, such as Ca, K, and Fe. Contrarily, Fe-BC application ameliorated Cd toxicity by triggering the activation of antioxidant enzymes (catalase and ascorbate peroxidase), primary and secondary metabolite accumulation (protein and phenolics concentrations), and by improving plant mineral nutrition under Cd treatment, compared with Cd treatment only. The ability of biosorbent material (Fe-BC) to adsorb the Cd ion on its surface and its immobilization from Cd-polluted soil to plant root was determined by using Langmuir and Freundlich isotherm models. Interestingly, Cd concentration was found in soil as diethylenetriamine (DTPA)-extractable soil Cd on radish root, but not reported in radish shoot with Cd+Fe-BC treatment, compared to Cd treatment; suggesting that Fe-BC treatment has a potential to provide extra strength toEBC the root and shoot, and plays an important role in regulation ionic and redox homeostasis under Cd stress