Document Type : Research Paper

Authors

• Sahar Sarafraz ¹
• Marzieh Ghanbari Jahromi ¹
• Marjan Diyanat ²

¹ Department of Horticultural Science, Science and Research Branch (SR.C.), Islamic Azad University, Tehran, Iran

² Department of Agronomy Science, Science and Research Branch (SR.C.), Islamic Azad University, Tehran, Iran

Abstract

Background and Objective: Salinity stress is one of the most significant environmental factors limiting plant distribution worldwide, as it induces a wide range of morphophysiological and biochemical changes. Seaweed extract, widely recognized as a natural biostimulant in modern agriculture, can enhance plant defense mechanisms and improve tolerance to various stresses. Its application has been shown to increase chlorophyll content and enhance photosynthetic efficiency, ultimately contributing to greater biomass accumulation and improved crop yield.
Materials and Methods: This study aimed to evaluate the growth, physiological, and biochemical responses of the medicinal plant Echinacea angustifolia L. under salinity stress and seaweed extract application. Salinity stress was applied at four levels (0, 50, 75, and 100 mM NaCl), and Sargassum johnstonii extract was used at three levels (no foliar application as control, 1 g/L, and 2 g/L). The experiment was conducted as a factorial arrangement in a completely randomized design (CRD) with three replications. Seeds were obtained from Pakan Seed Company and germinated in seedling trays under greenhouse conditions. After reaching the four-leaf stage, seedlings were transplanted into pots. Salinity treatments were applied via irrigation using sodium chloride solution (50 mL) every four days. To prevent salt accumulation, pots were leached with non-saline water after every three saline irrigations. Salinity stress was maintained for 40 days. Foliar application of the seaweed extract was performed at 10-day intervals, resulting in a total of five applications over the treatment period. At the end of the experiment, during the flowering stage, morphological traits were measured in the greenhouse, and plant samples were harvested for laboratory analyses at the Food Science Laboratory of Islamic Azad University, Nour Branch. Measured parameters included morphophysiological traits (plant height, leaf number, number of lateral branches, and fresh and dry weight of aerial parts), photosynthetic pigments (chlorophyll a and b), biochemical traits (proline and soluble sugars), and phytochemical characteristics (total phenols, total flavonoids, and antioxidant activity).
Results: The results indicated that the main effect of salinity stress was significant for all measured traits. The main effect of seaweed extract was significant for most traits, except proline content and antioxidant activity. In addition, the interaction between salinity stress and seaweed extract had a significant effect on all traits. Salinity at 100 mM NaCl markedly reduced plant growth, including plant height and the fresh and dry weight of aerial parts. Furthermore, the concentrations of photosynthetic pigments (chlorophyll a and b) declined with increasing salinity levels. However, the application of seaweed extract alleviated the detrimental effects of salinity stress on Echinacea angustifolia and moderated its impact. The highest values for most growth-related traits were observed under non-saline conditions with the application of 2 g/L seaweed extract. Overall, increasing the concentration of seaweed extract up to 2 g/L improved plant growth and performance across different salinity levels. At 75 mM NaCl, the highest accumulation of bioactive compounds, including total phenols, total flavonoids, and antioxidant activity, was recorded. Increasing seaweed extract concentration further stimulated the production of these compounds. Additionally, salinity stress led to increased accumulation of osmoprotectants such as soluble carbohydrates and proline compared to the control, which likely contributed to enhanced stress tolerance. Among the tested treatments, 2 g/L seaweed extract consistently showed the most positive effects on the evaluated traits, even under non-saline conditions.
Conclusion: Overall, the findings indicate that Echinacea angustifolia is relatively sensitive to salinity stress, with a pronounced decline in growth and yield observed under increasing salinity levels. Although the application of seaweed extract mitigated the adverse effects of salinity, the 2 g/L concentration was the most effective, playing a key role in reducing stress intensity by enhancing plant growth and promoting the accumulation of important metabolites.
 

Keywords

• Proline
• salinity stress
• Algae extract
• total phenols
• chlorophyll content

Main Subjects

• Agriculture and horticulture