Phytochemical responses of Dracocephalum kotschyi Boiss. to water deficit stress and different fertilizers.

A two-year field experiment was conducted at Tarbiat Modares University, Tehran, Iran, to evaluate the interactive effects of drought stress and fertilizer application on antioxidant defense systems and secondary metabolite accumulation in Dracocephalum kotschyi Boiss. Treatments included four irrigation regimes (20%, 40%, 60%, and 80% depletion of available soil water) and four fertilizer applications (urea, Nitroxin, vermicompost, and azocompost), with one unfertilized control. Mild to moderate drought significantly enhanced antioxidant enzyme activities (catalase, peroxidases, and polyphenol oxidase) and increased proline, phenolics, flavonoids, and anthocyanins, whereas severe water deficit reduced total protein content and intensified lipid peroxidation. Fertilizer type modulated these responses: organic amendments, particularly vermicompost and azocompost, stabilized antioxidant activity and mitigated oxidative damage, urea primarily stimulated enzymatic antioxidants, and Nitroxin promoted non-enzymatic antioxidant and osmolyte accumulation. Among treatments, azocompost under mild to moderate drought consistently produced the highest and most stable biochemical enhancement. These results suggest that integrating organic fertilization with deficit irrigation promotes regulated stress acclimation and coordinated secondary metabolism, providing a practical strategy to improve biochemical stress tolerance and phytochemical quality in this endangered medicinal species.