The biochar-based nanocomposites influence the quantity, quality and antioxidant activity of essential oil in dill seeds under salt stress.

The essential oil content and composition of medicinal plants may be influenced by eco-friendly products for nutrient availability under abiotic stresses. This research was conducted to determine the effects of biochar (30 g kg -1 soil) and biochar-based nanocomposites (BNCs) of iron (30 g BNC-FeO kg -1 soil), zinc (30 g BNC-ZnO kg -1 soil), and their combined form (15 + 15 g) on dill (Anethum graveolens L.) under salinity levels (non-saline, 6 and 12 dS m -1 ). Application of biochar, particularly BNCs increased iron and zinc content and decreased sodium accumulation in leaf tissues. The seed essential oil content increased under high salinity. Salinity changed the values of major compounds in essential oil and induced the formation of compounds such as alpha,2-dimethylstyrene, cuminyl alcohol, p-cymene, and linalool. Biochar treatments especially BNCs with a higher production of monoterpenes increased the levels of limonene, carvone, apiol, and dillapioll. All extracts showed a considerable DPPH-inhibitory effect with application of BNCs under salinity. The maximum antioxidant activity was observed under high level of salinity with application of the combined form. Therefore, the combined form of nanocomposite was the best treatment to improve the content of basic commercial monoterpenes and consequently antioxidant activity of essential oil in salt-stressed dill plants.