اثر محلول پاشی اسید هیومیک بر برخی ویژگی های مورفوفیزیولوژیکی و بیوشیمیایی نعناع سبز (.mentha spicata l) تحت تنش خشکی

به منظور بررسی اثرات تعدیل‌کنندگی اسید هیومیک بر تنش خشکی در گیاه نعناع سبز، آزمایشی گلدانی به صورت فاکتوریل در قالب طرح کاملا تصادفی با سه تکرار اجرا شد. تیمارهای آزمایش شامل تنش خشکی در سه سطح (30، 70 و 100 درصد ظرفیت زراعی) به عنوان فاکتور اول و محلول‌پاشی اسید هیومیک در چهار سطح (صفر، 100، 500 و 1000 میلی‌گرم در لیتر) به عنوان فاکتور دوم بودند. نعناع سبز قادر نبود بیش از 2 هفته تنش 30 درصد ظرفیت زراعی را تحمل کند و به طور کامل گیاهان این سطح نابود شدند. صفات رویشی گیاه از قبیل ارتفاع بوته، تعداد شاخه فرعی، طول برگ، عرض برگ و وزن تر و خشک برگ و ساقه در تنش ملایم خشکی (70 درصد ظرفیت زراعی) کاهش معنی‌داری نسبت به تیمار شاهد نشان دادند. محلول‌پاشی اسید هیومیک به ویژه غلظت 1000 میلی‌گرم در لیتر تحت تنش خشکی سبب بهبود این صفات نسبت به گیاهان شاهد گردید. بیشترین مقادیر رنگیزه‌های فتوسنتزی در تنش خشکی 70 درصد ظرفیت زراعی و محلول‌پاشی 1000 میلی‌گرم در لیتر اسید هیومیک و کمترین آنها در تیمار عدم تنش خشکی و کاربرد 500 میلی‌گرم در لیتر اسید هیومیک مشاهده شد. بالاترین میزان فنل کل (0.62 میلی‌گرم/گرم وزن تر) و فعالیت آنتی‌اکسیدانی عصاره برگ (60.16 درصد) در گیاهان حاصل از محلول‌پاشی 1000 میلی‌گرم در لیتر‌ اسید هیومیک تحت تنش ملایم خشکی مشاهده شد. بیشترین محتوی رطوبت نسبی در شرایط عدم تنش و محلول‌پاشی 1000 میلیگرم در لیتر اسید هیومیک حاصل شد. بنابراین می‌توان’گفت که نعناع سبز گیاهی بسیار حساس به تنش خشکی است و با توجه به کاهش ‌شاخص‌های رشد و فرایندهای فیزیولوژیکی ناشی از تنش خشکی کاربرد اسید هیومیک به‌ویژه در غلظت بالا بصورت محلول‌پاشی می‌تواند به عنوان کود آلی همراستا با کشاورزی پایدار در تنظیم پتانسیل اسمزی نعناع سبز تحت شرایط تنش خشکی ملایم تا حدودی موثر باشد.

The effect of humic acid foliar application on some morphophysiological and biochemical characteristics of spearmint (Mentha spicata L.) in drought stress conditions

IntroductionSpearmint is one of the plants that attracted the attention of researchers because of its economic and pharmaceutical importance. This plant is one of the most important and most famous species of mint which disperses in different parts of the world. One of the scarce resources that is affected by rainfall is water. The effect of water stress depends on the duration, durability and amount of deficiency. One of the most important factors limiting the growth of plants around the world is drought, which is the most common environmental stress. One of the most effective mechanisms that is used by plant in water stress condition is osmotic regulation. The accumulation of proline and soluble sugars (as the most important osmolite) in regulation of osmotic is done to dominate the negative effects of drought stress. Results of researches have shown that drought stress has effective effect on the growth and biochemical characteristic of plants, and it differs among different plants. Optimum plant nutrition is one of the effective methods for plant resistance in drought conditions. Humic acid is one of the most important fertilizers in the agriculture. It creates more space for water penetration by modifying physical soil characteristic and improving soil granulations. Humic acid increases the activity of photosynthesis by increasing the activity of the Robisco enzyme. To consider the high importance of spearmint as a valuable vegetable and medicinal plant, the aim of this study was to estimate the resistance of spearmint to different levels of drought stress and evaluate the effects of foliar application humic acid as a moderator factor in drought stress condition. Materials and methodsA pot research was conducted in factorial experiment in a completely randomized design with 3 replications to investigate the effects of humic acid as a growth factor and moderator of the effect of drought stress, on Mentha spicata L. at the Faculty of Agriculture, Ferdowsi University of Mashhad. The first factor was three levels of drought stress (30, 70 and 100 % FC) and the second factor was four levels of humic acid (0, 100, 500 and 1000 mgL1). At the firstly, spearmint rhizomes with 10 cm length were prepared with at least 2 buds. In the middle of March, about 4 rhizomes were cultivated in depth of 5 cm of pots soil. Foliar application of humic was used at three stages (one week before drought stress and one and three weeks after applying drought stress) on the plant surface. We didn’t use any humic acid on the control treatment. About 4 weeks after humic acid application, the morphological, physiological and biochemical traits were measured at flowering stage. ResultsVegetative traits such as plant height, number of branches, leaf length, leaf width and fresh and dry weight of leaf and stem showed a significant decrease with increasing drought stress (70% of field capacity) in compared to control treatment. Foliar application of humic acid, especially 1000 mgL1 improved these traits in compared to control plants in drought stress condition. Also, the mean comparison of the interaction treatments showed that the highest amounts of photosynthetic pigments was observed at 70% FC and application of 1000 mgL1 of humic acid and the least one was belonged to control treatment and application of 500 mgL1 of humic acid. The highest antioxidant activity of leaf extract (80.66%) and total phenol (0.87 mg/g fresh weight) were observed in plants treated with 1000 mgL1 humic acid and 70% FC. The highest relative water leaf content was obtained at nonstress conditions (control) and the foliar application of 1000 mgL1 of humic acid. ConclusionThis study showed that spearmint is very susceptible to drought stress, which could not withstand drought stress of 30% FC even for a short time. In general, means comparison of results showed that drought stress significantly reduced the morphological traits of spearmint. Also, the interaction treatments showed that the using of 1000 mgL1 humic acid had the greatest effect on the growth indices. The highest amounts of photosynthetic pigments was observed at 70% FC and foliar application of 1000 mgL1 of humic acid and the lowest one was belonged to control treatment of humic acid and without stress condition. Also, the highest levels of total phenol and antioxidant activity were observed in 70% FC and 1000 mgL1 humic acid treatment. Therefore it can be stated that spearmint is high susceptible plant to drought stress because of sever effects of drought stress on its growth characteristics and physiological processes. The foliar application of humic acid, especially at high concentration (1000 mgL1) can be effective in regulating the osmotic potential under slightly drought stress conditions. So, it can be used as an organic fertilizer in sustainable agriculture.