Physiological and biochemical alterations in soybean by banana peel biochar under different degrees of salt stress

Salt influences cellular membranes by the excessive production of reactive oxygen species, while osmolytes play a vital role in protecting plants from oxidative stress caused by salt. Biochar may alleviate the effects of salinity-induced stress on crops. The study investigated the impact of biochar supplementation on osmolyte modifications and antioxidant activity in soybean (Glycine max cv. AARI) under salt stress conditions. Soybean plants were exposed to 3 salinity levels (without salinity, 5, and 10 dSm^- 1 NaCl), and different levels of biochar (without biochar, 12.5%, and 25% w/w). Root and shoot dry weight were reduced by 17% and 21%, respectively, under both salt-induced stress regimens. Salinity elevated the activities of superoxide dismutase (SOD), polyphenol oxidase (PPO), peroxidase (POD), ascorbate peroxidase (APX), and catalase (CAT) as well as O₂•^- (oxygen radicals), MDA (malondialdehyde), and H₂O₂ (hydrogen peroxide) levels by 3.1-fold, 1.8-fold, 3.1-fold, 2.8-fold, 4.4-fold, 1.4-fold, 2.2-fold, and 2.3-fold in plants relative to control group. Furthermore, higher concentrations of soluble protein, soluble carbohydrates, glycine betaine, and proline were more pronounced at 10 dSm^- 1 than at 5 dSm^- 1. In contrast, incorporating biochar into soil enhanced both root and shoots dry weight by 47% and 53% respectively, compared to the absence of biochar application. Furthermore, the antioxidant levels in soybean seedlings cultivated in soil treated with biochar, particularly at a concentration of 25% biochar, decreased. Adding biochar led to a notable decrease in H₂O₂ (27%), O₂^•-(19%), and MDA (22%) concentrations, along with a reduction in the accumulation of osmotic substances in both roots and leaves. The findings demonstrate that the incorporation of biochar can safeguard soybean seedlings from NaCl-induced stress by alleviating oxidative damage.