Assessing the role of cattle manure-derived biochar in stress mitigation of mung bean seedlings growing in arsenate-enriched soil.

Arsenic (As) contamination of agroecosystems is one of the most emerging threats affecting crop quality and human health. Thus, there is an insistent need to develop sustainable strategies for mitigating As-contamination and its impact on plants. Biochar, a porous carbonaceous material mainly derived from waste biomass, is known to sequester toxic elements from various substrates, including contaminated soil, and is considered a viable and sustainable option for remediation as well as stress mitigation. The present study evaluated the prospective role of a biochar derived from cattle manure in mitigating arsenate (As) induced stress in mung bean seedlings. The As stress imposition caused a decline in plant growth, which was observed in the inhibition of root and shoot elongation and biomass. The imposition of As stress in the absence of biochar amendment resulted in a strong increase in hydrogen peroxide (HO) and superoxide radical (O) production, while HO and O contents declined significantly (p ≤ 0.01) in the root and shoot of mung bean seedlings grown in biochar-amended soil during As stress. With a substantial reduction in reactive oxygen species (ROS) overproduction in mung bean seedlings grown in biochar-amended soil, we observed a significant (p ≤ 0.01) decline in malondialdehyde (MDA) content in the root and shoot during As stress under biochar-amended conditions compared to those under As stress in the absence of any biochar amendment. The impact of biochar was also observed in terms of antioxidant activities of enzymes such as catalase (CAT) and superoxide dismutase (SOD), which showed significantly higher (p ≤ 0.01) activities in both root and shoot during As stress compared to those under As stress alone. However, the effect of biochar amendment in alleviating the levels of non-enzymatic antioxidants such as ascorbate (AsA) and total glutathione (GSH) was not markedly altered from those under As stress in the absence of biochar amendment. The SEM-EDX analysis also showed that biochar amendment improved the elemental composition of mung bean seedlings during As stress in both root and shoot by fortifying Si, Mg, Fe, Cu, Ca, and Zn; at the same time, it restricted the uptake and accumulation of As in both root and shoot. Since the biochar was amended at 1.5% and 2.0% per kg of soil, the effect of 2.0% biochar amendment was found to be more effective in alleviating As-induced stress responses in mung bean seedlings. Our results suggested a prospective role of cattle manure biochar in alleviating As-induced stress responses in mung bean seedlings by restricting As accumulation and fortifying the essential nutrient elements to uphold the nutrient imbalance induced by As stress, as well as modulating ROS production and uplifting antioxidant defense metabolism.