Characterization of biochar derived from bamboo and its application to modulate the toxic effects of chromium on wheat plant

Soil pollution with heavy metals has become a global issue that can be addressed via immobilization through the application of biochar. In the present study, we hypothesized that biochar derived from bamboo helps mitigate the toxicity of chromium (Cr) in wheat plants grown in soil contaminated with Cr at 0, 50, 100, and 200 mg kg⁻¹. The biochar produced was brittle, porous, and alkaline with a surface area of 46.93 m² g⁻¹and pore size of 0.04 cm³ g⁻¹. The elemental composition of biochar was carbon (C = 77.63%), oxygen (O = 18.32%), hydrogen (H = 2.81%), calcium (N = 1.07%), and sulfur (S = 0.17%) determined through energy-dispersive X-ray spectroscopy. Fourier transform infrared (FTIR) spectroscopy revealed the occurrence of carboxylic or phenolic, aliphatic, amide, and aromatic groups. The results of the toxicity study revealed that the interaction of various concentrations of Cr and biochar was significant for shoot and root biomass because both the parameters were sensitive to Cr at higher concentrations. For instance, Cr concentration with 50, 100, and 200 mg kg⁻¹ reduced shoot dry biomass by 30.54%, 45.45%, and 69.94%; root dry biomass by 26.40%, 43.39%, and 57.14%; carotenoid contents by 5.50%, 25.86%, and 24.92%; stomatal conductance by 23.46%, 35.60%, and 44.34%; photosynthetic rate by 12.11%, 25.59%, and 40.16%; LRWC by 7.01%, 15.12%, and 26.52%; intercellular concentration by 10.95%, 20.73%, and 35.335%. In addition, wheat growth parameters such as proline and malondialdehyde (MDA) contents were increased in the presence of Cr in the range of 4.93 to 102.46% in roots, while 20 to 81.86% in shoots. Similarly, superoxide dismutase (SOD) and hydrogen peroxide (H₂O₂) activities in roots were enhanced in the range of 7.26 to 84.81% and 34.63 to 93.74%, and 15.63 to 76.73% and 77.25 to 190.86% in shoots after the exposure of wheat plants to Cr at 50, 100, and 200 mg kg⁻¹. On the other hand, catalase (CAT) and peroxidase (POD) activities in shoots were significantly reduced upon exposure to Cr at 100 and 200 mg kg⁻¹ suggesting that it was beyond the capacity of these antioxidants to scavenge reactive species. It was noted that biochar application at 10% significantly (P < 0.05) reduced MDA, proline contents, SOD, CAT, POX, and H₂O₂ activities in roots and shoots alleviating Cr toxicity at lower levels of treatments. Therefore, the present study concluded that strict measures should be taken for the removal of Cr from wastewater before they are discharged and used for irrigation purposes because the toxic effects of Cr were not completely alleviated at higher levels of Cr in the presence of biochar.