Effects of biochar and drought stress on some protective mechanisms of Nigella sativa L.

Nigella sativa L. is a valuable medicinal plant that is widely used in different industries. Accumulation of compatible osmolytes is one of the common responses of plants under drought stress. To investigate the effects of irrigation regimes and biochar (resulting from the heating of cattle manure) on N. sativa, a factorial experiment was conducted in a completely randomized design with three replications in the greenhouse of the Faculty of Agriculture at the University of Kurdistan in 2018. The experimental factors consisted of three drought stress levels (40, 70, and 100% of FC) and two biochar use levels (0 and 15 tons.ha-1). The ANOVA results showed that the interaction effects of drought stress and biochar were significant on hydrogen peroxide, malondialdehyde, superoxide dismutase, peroxidase, proline, soluble carbohydrates (water and ethanol soluble), and osmotic potential. Increasing the intensity of drought stress enhanced the amount of hydrogen peroxide, malondialdehyde, superoxide dismutase, peroxidase, proline, and soluble carbohydrates (water and ethanol soluble) and caused the osmotic potential to become more negative. Biochar application decreased the negative effects of drought stress so that hydrogen peroxide, malondialdehyde, superoxide dismutase, peroxidase, proline, and soluble carbohydrates (water and ethanol soluble) amounts were lower than the treatments without biochar. Overall, the present research results proved the useful and effective role of biochar in improving the physiological traits and protective osmolytes of N. sativa under drought stress.