Cadmium (Cd) contamination in agricultural soils has become one of the most widespread and severe environmental and agricultural problems in Asian countries (Mori et al., 2016). There are different methods to decrease the harmful and toxic effects of heavy metals in plants. Organic additives such as biochar (BC) have been exposed as highly effective and environment-friendly immobilizers to decrease Cd concentrations (Hamid et al., 2020). BC is a black porous carbon-rich compound that produced from the pyrolysis, thermochemical modification of a wide range of organic substances like agricultural wastes and woody materials at moderate to high temperatures in the absence or low oxygen conditions (Ali et al., 2017). BC application decreases trace element toxicity and enhances metal immobilization (Khan et al., 2020). Therefore, a pot factorial experiment based on a completely randomized design with four replications was performed to evaluate the effect of BC on growth, antioxidant enzyme activities, and Cd concentration of Ocimum ciliatum L. leaves under Cd stress. The experimental treatments comprised BC levels (0, 1, and 2% w/w of soil) and Cd concentrations (0, 20, and 40 mg/kg). According to the results of this study, the highest aboveground biomass was observed by using 2% w/w BC with no Cd. In addition, the highest malondialdehyde (MDA) content, cell membrane injury, guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) activities were obtained in 40 mg/kg Cd with no BC treatment and using BC reduced them to mitigate negative impacts of Cd stress. On the other hand, the Cd concentration of the leaves decreased by using BC especially at 2% w/w of soil. In total, BC can apply as an environmental friendly amendment in contaminated soil to alleviate the harmful effects of Cd on the plants. Moreover, Cd concentration in the leaves reduces due to the absorption properties of BC.

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