The effect of root zone temperature at low nitrogen level of nutrient solution on sweet pepper

Abstract

Low temperatures can inhibit plant growth and development, and cause physiological problems by damaging membrane lipids, proteins, and nucleic acids. A factorial experiment based on a complete randomized design with five replicates investigated the effect of root zone temperature and nitrogen ratio on sweet pepper seedlings in soilless culture. Treatments include root zone temperature (15, 25 (optimum), and 35 °C) and different nitrogen levels: 50, 75, and 100% (optimum) of N Johnson nutrient solution. The results showed that growth parameters including root fresh weight, shoot dry weight, and root volume reduced more at 15 °C with nitrogen level reduction compared with 35 °C. Photosynthetic characteristics like photosynthetic rate, transpiration, mesophyll conductivity, and photosynthetic water use efficiency were not affected by nitrogen levels at 25 and 35 °C. Also, higher photosynthetic traits, including greenness index, photosynthesis rate, and mesophyll conductance, were obtained with N50% at 15 °C. Shoot phenol increased by 55% at N 50% compared with N 100% at 35 °C. Sweet peppers seedlings were more sensitive to high root zone temperature of 35 °C. Heat stress and nitrogen deficiency in the root zone ambient led to poor growth, lower photosynthetic capacity, higher phenolic compound, lower nitrate reductase activity, and higher nitrogen compound in evaluated seedlings. Nitrate reductase activity was affected by heat stress and significantly decreased at 35 °C. The phosphorous and potassium concentration was reduced by nitrogen reduction at 35 °C. Conclusively, a lower nitrogen level in the nutrient solution can be used for sweet pepper seedlings’ growth if the temperature of the nutrient solution is decreased to 15 °C.