اثر تنش خشكي بر خصوصيات فلورسانس كلروفيل و عملكرد علوفه دو رقم ارزن علوفه‌اي (Pennisetum americanum var. nutrifeed and Punicum sp var. pishahang)

Effect of Drought Stress on Chlorophyll Fluorescence and Forage Yield of Two Forage Millet Cultivars (Pennisettum americanum var nutrifeed and Punicum sp var. pishahang)

به‌منظور بررسی اثر تنش خشكی روی برخی ویژگی‌های فیزیولوژیكی دو رقم ارزن علوفه‌ای آزمایشی به‌صورت فاكتوریل در قالب طرح بلوك كامل تصادفی با سه تكرار در مزرعه تحقیقاتی دانشگاه شهید چمران اهواز انجام شد. عامل اول دو رقم ارزن علوفه‌ای‌ شامل نوتریفید و پیشاهنگ و عامل دوم تنش خشكی در چهار سطح شامل تأمین 100درصد نیاز آبی به‌عنوان شاهد، 75، 50، 25 درصد نیاز آبی بود. مقدار آب آبیاری در هر تیمار بر مبنای 50، 100، 150 و 200 میلی‌متر تبخیر از تشتك تبخیر كلاس A محاسبه شد. بیشترین عملكرد ماده خشك در رقم نوتریفید در شرایط شاهد و كمترین عملكرد ماده خشك در رقم پیشاهنگ در 25 درصد تأمین نیاز آبی به‌دست آمد. میزان پرولین و نفوذپذیری نسبی غشاء در هر دو رقم طی تنش همواره بیشتر از شاهد بود و با افزایش سطح تنش خشكی میزان پرولین افزایش یافت. بیشترین میزان نفوذپذیری نسبی غشا در رقم پیشاهنگ در 25 درصد تأمین رطوبت و كمترین میزان نفوذپذیری نسبی غشاء در رقم نوتریفید در شاهد به‌دست آمد. با افزایش سطح تنش محتوای نسبی آب برگ، عملكرد ماده خشك، پتانسیل اسمزی، هدایت روزنه‌ای، بیشینه كارآیی فتوسنتزی فتوسیستم ΙΙ (Fv/Fm)، فرود فتوشیمیایی (qP) و عملكرد كوآنتومی فتوسیستم دو كاهش یافتند. عملكرد ماده خشك همبستگی مثبت و معنی‌دار با هدایت روزنه‌ای، محتوای نسبی آب برگ، شاخص كلروفیل (عدد SPAD)، عملكرد كوآنتومی فتوسیستم ΙΙ و Fv/Fm داشت. ارزن نوتریفید نسبت به رقم پیشاهنگ هم در شرایط غیر تنش و هم در شرایط تنش از كارایی مصرف آب بهتری برخوردار بود و به‌نظر می‌رسد این رقم در شرایط محدودیت آب آبیاری بتواند از تولید علوفه مناسبی برخوردار باشد.

Introduction Drought is dangerous to the successful production of agricultural products around the world. When drought occurs a combination of physical and environmental factors causes internal stress in plants and reduces production. Photosystem II plays an important role in higher plants to response the environmental factors. In recent years chlorophyll fluorescence techniques in ecophysiology have been considered as a rapid, sensitive and non-destructive method. Dry matter reduction can be due to cell swelling and pressure reduction because of reduced leaf area and photosynthetic pigments, especially chlorophyll. RWC is the best criteria of plant water status measurement. When plants affects by drought, salinity, low temperatures and other factors that reduce water potential of the cell sap they should increase their organic solute concentration to continue water absorption under stress conditions (osmotic adjustment). The aim of this study was investigating drought stress effects on photosynthesis and dry matter yield of two forage millet cultivars including Nutrifeed and Pishahang along with a discussion of some physiological characteristics and chlorophyll fluorescence change. Materials and Methods This experiment was carried out as factorial layout based on randomized complete block design with three replications at the Agricultural Research Station, Shahid Chamran University in 2010-2011. First factor was two forage millet cultivars including Nutrifeed and Pishahang. The second factor was three water stress levels as mild, moderate and severe drought including providing 100, 75, 50 and 25% water requirement. The amount of water in each treatment based on the 50, 100, 150, and 200 mm evaporation from class A evaporation pan that located in meteorology synoptic station in the vicinity of the research farm was calculated. The crop coefficient (Kc) was determined based on evapotranspiration and soil water depletion treatments and then set the curve traced FC and soil moisture, the amount of water requirement was calculated and finally the volume of irrigation water for treatments was provided. Traits including stomatal conductance, relative concentration of chlorophyll SPAD-502 osmotic potential, relative permeability of the membrane, proline, relative water content and chlorophyll fluorescence of the last developed leaf (leaf ligule was observed) in two conditions light adapted and dark adapted leaves were measured. Results and Discussion Results showed that the effect of stress levels on all traits was significant. The highest and lowest yield of dry matter were observed in the control treatment of Nutrifeed cultivar and 25% water requirement supply of Pishahang cultivar, respectively. Proline and relative permeability of the membrane over drought stress was more than the control in both cultivars and proline increased with increasing drought levels. The highest and lowest relative permeability of the membrane were observed in the Pishahang cultivar at 25% moisture supply and the control treatment of Nutrifeed cultivar, respectively. As increasing the stress intensity, relative water content, dry matter yield, osmotic potential, stomatal conductance, Fv/Fm, and qP, decreased. Dry matter had significant positive correlation with stomatal conductance, relative water content, SPAD value, Quantum yield of PSII, and Fv/Fm. It should be noted that Nutrifeed cultivar compared to the Pishahang cultivar under both normal and stress conditions had better water use efficiency. So it seems that Nutrifeed cultivar could be used as a suitable forage under water deficit conditions. Conclusions It seems that Nutrifeed cultivar is a suitable fodder crop for livestock feed production in the areas with water restrictions.