بررسی اثر سیلیسیم بر جذب فسفر و رشد گیاه گندم در شرایط تنش خشکی

یکی از راه‌های مقابله با تنش خشکی مدیریت عناصر غذایی گیاه ازجمله سیلیسیم است که می‌تواند رشد و جذب عناصر غذایی برخی ‌از گیاهان را در شرایط تنش خشکی بهبود ببخشد. آزمایشی گلخانه‌ای جهت بررسی اثر سیلیسیم بر جذب فسفر و رشد گیاه گندم در شرایط تنش خشکی به‌‌صورت فاکتوریل در قالب طرح کاملاً تصادفی با سه تکرار انجام شد. تیمارهای این آزمایش شامل سه سطح سیلیسیم (صفر،50 و150 میلی‌گرم بر کیلوگرم خاک)، سه سطح فسفر (صفر، 25 و50 میلی‌گرم بر کیلوگرم خاک) و دو سطح تنش خشکی (45 و 100 درصد ظرفیت زراعی خاک) بودند. بر اساس نتایج، تنش خشکی سبب کاهش معنی‌دار 55.4 و 41.5 درصدی وزن تر و خشک اندام هوایی شد؛ همچنین غلظت و جذب فسفر در اندام ‎‌هوایی را به‌ترتیب 13.6 و 49.8 درصد کاهش ‌‌داد. با افزایش غلظت سیلیسیم وزن تر و خشک گیاه در هر دو شرایط با و بدون تنش خشکی تغییر معنی‌داری نداشت. افزایش سیلیسیم باعث کاهش جذب و غلظت فسفر در شرایط بدون تنش شد ولی در شرایط تنش خشکی اختلاف معنی‌داری در غلظت و جذب فسفر مشاهده‌ نشد؛ بنابراین به نظر می‌رسد علی‌رغم برخی توصیه‌ها در استفاده از سیلیسیم در شرایط تنش در خاک‌های آهکی، کاربرد سیلیسیم جهت مقابله با تنش خشکی در گندم همواره اثرات مثبت ندارد و میزان تاثیرگذاری آن می‌تواند به مقدار اولیه سیلیسیم خاک مربوط باشد.

The effect of silicon on phosphorus uptake and wheat growth under drought stress in a calcareous soil

Introduction Drought stress is one of the major physical stresses that have adverse effects on plant growth and metabolic processes such as nutrient uptake. Some researchers reported that silicon can improve plant growth and regulation of phosphorus uptake under drought stress; But Gao et al. (2004) did not observe a significant increase in fresh and dry weight under waterdeficit stress induced by polyethylene glycol in maize. On the other hand, silicon did not have a significant effect on shoot dry matter and phosphorus concentration in wheat flag leaves under nonstressed condition (Sarto et al., 2014). Therefore, due to the increase in consumption of silicon fertilizer in our country to cope with drought stress, this experiment was conducted to investigate the influence of silicon on phosphorus uptake and wheat growth under water deficient conditions.  Materials and methods A threefactor experiment was carried out in a completely randomized design with three replications in research greenhouse of ferdowsi university of Mashhad. The experiment factors were three levels of silicon (0, 50 and 150 mg kg1), three levels of phosphorus (0, 25 and 50 mg kg1) and two levels of moisture stress (45 and 100% of field capacity). Soil samples were taken from 030 cm depth. The pots were filled with 5 kg of soil. Silicon and phosphorus were added to the soil in the form of sodium silicate (Na2SiO3) and calcium phosphate (Ca(H2PO4)2.H2O) respectively. Ten seeds of wheat were sown in each pot and then thinned to 3 plants per pot after seedling establishment. Soil moisture was kept at about level of field capacity for two weeks. Moisture stress treatments were imposed by weighing the pots every day. The plants were irrigated with distilled water for 50 days after sowing. Then, harvested, ovendried and grinded. Soil samples were airdried and passed through a 2 mm sieve. Shoot fresh and dry weights, silicon and phosphorus concentrations in shoots and silicon concentration in soil samples were measured. Minitab 17 software was used for data analysis. The comparison of means was performed by using Tukey test at 5% probability level.  Results and discussion According to the results, shoot fresh and dry weights were decreased by 55.4% and 41.5% under moisture stress. Also, concentration and uptake of phosphorus reduced by 13.6% and 49.8% under water deficient conditions. Moreover, application of 25 mg kg1 phosphorus increased the plant fresh and dry weights in both stress and nonstressed conditions. Shoot fresh and dry weights did not change significantly with increasing silicon supply under different soil moisture levels. Silicon application decreased shoot phosphorus cocentration and uptake at field capacity, however, phosphorus concentration and uptake were not significantly affected by silicon at the 45% FC level. The interaction of silicon and moisture stress factors indicated that by increasing silicon concentration in the soil, no significant changes were observed in silicon uptake under stress conditions. Also, silicon concentration and availability in the soil were increased by solubility of soil silicates after plant cultivation. As a result, the effect of silicon on fresh and dry weights, shoot phosphorus concentration and uptake was not significant. Thus, further studies are needed to use silicon in calcareous soils for wheat under moisture stress.  Conclusions The results showed that moisture stress significantly reduced shoot fresh and dry weights, silicon and phosphorus concentration of shoot and uptake of silicon and phosphorus. But, silicon addition did not alter the silicon uptake. It appears that the concentration of plantavailable silicon in soil was increased by solubility of soil silicates after plant cultivation. Thus, plant did not respond to silicon fertilization and application of silicon in soil could not reduce the negative effects of moisture stress. Therefore, the initial concentration of silicon should be considered for silicon fertilizer recommendation to overcome moisture stress constraints in wheat cultivation in calcareous soils.