The biostimulatory effect of microalgae extracts upgrades salt tolerance and antioxidant capacity in flowers and shoots of Cuminum cyminum L.

While cumin seeds are widely recognized for their culinary and medicinal properties, the phenolic compounds present in the plant’s flowers and shoots have received limited attention, particularly regarding their role in stress tolerance and antioxidative properties. Microalgae derivatives have emerged as potent biostimulants capable of modulating secondary metabolism and improving stress resilience in crops. However, their specific impact on cumin plants remains unknown. Therefore, this study aimed to investigate the effects of Dunaliella salina, Chlorella vulgaris, and Arthrospira platensis extracts on mitigating salt stress and antioxidant responses in two ecotypes of cumin, namely Mashhad and Sabzevar. Results indicated that salinity reduced biomass, tolerance index, and total chlorophyll and carotenoid contents, while increasing electrolyte leakage, total phenolic content (TPC), and the activities of ascorbate peroxidase and superoxide dismutase. Microalgal extracts increased the levels of photosynthetic pigments, biomass, and tolerance index. This treatment significantly decreased the EL level by increasing the activity of antioxidant enzymes and enhancing TPC. The application of microalgae extracts increased antioxidant capacity, as evidenced by decreased IC50 for DPPH scavenging activity, carotene bleaching, and reducing power in both flowers and shoots under saline and non-saline conditions. Among the extracts, D. salina exhibited the highest efficacy in enhancing antioxidant responses in cumin plants, particularly in the Mashhad ecotype. These findings indicate that the application of microalgae extracts could serve as an innovative approach to improving salt tolerance in plants while simultaneously increasing the antioxidant properties and industrial value of medicinal herbs.