| چکیده انگلیسی مقاله |
Background and objectives: Water availability is one of the most critical climatic factors influencing plant distribution worldwide. Drought stress, resulting from insufficient water availability, can induce plant morphophysiological, biochemical, and functional changes. Seaweed contains a high percentage of polymer compounds capable of absorbing water molecules and forming a gel-like structure. Additionally, its rich composition of salts and essential minerals fulfills plant nutrient requirements, promotes growth and yield, enhances resistance to environmental stress, improves nutrient uptake from the soil, and boosts antioxidant properties. Tarragon (Artemisia dracunculus L.) is an herb widely used as a flavoring agent in the food industry, with its essential oil playing a key role in canning and perfumery. Because seaweed extract serves as a natural biofertilizer, providing essential nutrients and plant growth hormones while being environmentally friendly, it represents a viable alternative to chemical fertilizers. Moreover, it enhances plant resilience to various environmental stresses and contributes to sustainable food production. This study aims to investigate the effects of seaweed extract on the growth and biochemical characteristics of tarragon under drought stress conditions.
Methodology: This study was conducted to investigate the growth, physiological, and biochemical characteristics of the medicinal plant tarragon (Artemisia dracunculus L.) under drought stress at four levels (100%, 80%, 60%, and 40% field capacity) and foliar application of aqueous Sargassum seaweed extract at three concentrations (0 g/L [control], 1 g/L, and 2 g/L). The experiment was carried out in the spring of 2023 in a greenhouse located in Damavand, using a factorial arrangement based on a completely randomized design with three replications. Four-leaf tarragon seedlings were obtained from the training farm of Damavand Technical and Vocational School and transplanted into three-liter pots. After a 10-day establishment period, drought stress was applied for 45 days, with foliar spraying of seaweed extract performed every two weeks, starting simultaneously with the onset of drought stress. Soil moisture levels in the pots were monitored daily by weighing them, and water was added as needed to maintain the target field capacity for each treatment. Plant sampling was conducted one week to 10 days after the completion of treatments, coinciding with the transition from vegetative to reproductive growth. Morphophysiological traits, including fresh and dry biomass, plant height, and the number of secondary branches, were measured. Additionally, biochemical parameters such as proline content, soluble carbohydrates, total phenol and flavonoid content, antioxidant activity, and essential oil yield and percentage were analyzed.
Results: The results indicated that under severe drought stress (40% field capacity) and in the absence of seaweed extract application, there was a significant reduction in morphophysiological traits, including plant height, main stem diameter, number of secondary branches, fresh and dry weight of aerial parts, and photosynthetic pigments (chlorophyll a, chlorophyll b, and total chlorophyll). However, the application of seaweed extract mitigated the adverse effects of drought stress on tarragon. Under mild drought stress (60% field capacity) without seaweed extract application, the highest levels of total phenol (82 mg/g gallic acid), total flavonoid (64.33 mg/g quercetin), antioxidant activity (76%), and essential oil yield and percentage were observed. Drought stress also enhanced the activity of antioxidant enzymes, leading to increased synthesis of soluble carbohydrates and proline compared to the control. Among the tested seaweed extract concentrations, the application of 2 g/L had the most significant positive impact on the evaluated traits, further improving plant resilience and biochemical responses under drought-stress conditions.
Conclusion: The overall findings of this study indicate that tarragon exhibits limited resistance to drought stress, with a noticeable decline in yield as stress intensity increases. Under drought conditions, the application of seaweed extract, particularly at a concentration of 2 g/L, effectively mitigated the adverse effects of stress by enhancing morphophysiological and phytochemical traits, including total phenol, flavonoid content, and essential oil yield. In most cases, the difference between 2 g/L and 1 g/L of seaweed extract was statistically significant, with 2 g/L demonstrating superior effectiveness. Therefore, the application of 2 g/L seaweed extract is recommended to improve drought tolerance and maintain yield in tarragon under water-limited conditions. |