Salinity stress is one of the most important environmental factors that substantially afects the yield of plants and changes their secondary metabolites worldwide. Biochar is a vital eco-friendly amendment widely used to improve soil health and promote plant productivity under stress conditions. In the present study, the efect of biochar, a carbon-rich organic substance (0, 1, 2, and 3% of the total mass of the pot), on agro-morphological and physiological traits, essential oil and carvacrol percentage, and antioxidant activity of Satureja khuzistanica under salt stress conditions (0, 2, 4, and 8 ds m−1 NaCl). The plant agro-morphological traits and yield, including plant height, number of main and secondary branches, length and width of leaf, fresh and dry weight of aerial parts, and dry weight of leaves and fowers were decreased with increasing salinity level, but these traits were improved with the application of biochar. The highest yield was observed in the 3% biochar treatment in normal conditions. The highest percentage of essential oil (3.55%) and carvacrol (97.66%) were obtained from the plants under salinity stress (8 ds m−1) treated without and with 3% biochar. With increasing levels of salinity stress, the amount of SPAD decreased, and electrolyte leakage (EL) and the activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) enzymes increased. However, biochar treatments efectively reduced the damage caused by salinity stress, so that the addition of 3% biochar treatment will decrease the destructive efects of salinity stress in the S. khuzistanica, so that decreased EL content and the activity of POD, SOD, and CAT enzymes. According to the positive efects of biochar on functional traits, essential oil content, carvacrol percentage, and SPAD index, its application can be suggested as a sustainable strategy to increase the yield of S. khuzistanica under salinity stress.
