Physiological Response of Quinoa to Nitrogen Application under Salinity Conditions

Salinity stress is one of the major abiotic stresses which injures plants by limited water absorption and nutrient imbalance and limits crop growth. In order to study the effect of nitrogen fertilizer on physiological traits of quinoa at high salt concentrations, a greenhouse experiment was conducted in a factorial arrangement based on a randomized complete block with three replications in 2019. The first factor included 5 levels of salinity (100 (control), 200, 300, 400, 500 mM) and the second factor comprised of 4 levels of nitrogen fertilizer (50, 100, 150 and 200 ppm). Traits that were measured included quantum yield, photosynthetic efficiency index, shoot dry weight, proline content, soluble sugar content, malondialdehyde content, catalase and peroxidase activity, shoot potassium and sodium content. Results showed that quantum yield, proline content and soluble carbohydrate were affected by salinity and nitrogen concentration. With increasing salinity levels from 100 to 500 mM, quantum yield, proline and soluble carbohydrate content increased, but with increasing nitrogen levels from 50 ppm to 200 ppm soluble carbohydrate and proline content decreased and increased, respectively. Shoot dry weight, malondialdehyde content, catalase and peroxidase activity, shoot sodium and potassium content were affected by the interaction of salinity and nitrogen levels. Results showed that at high levels of salinity and increasing nitrogen levels to 150 and 200 ppm, shoot dry weight and shoot potassium content decreased, also malondialdehyde, catalase, and peroxidase activity and shoot sodium content increased. According to these results, in low (100 and 200 mM) and medium (300 mM) salinity levels application of 200 ppm nitrogen and in high salinity (400 and 500 mM) levels application of 50 ppm nitrogen in nutrient solution of quinoa is reasonable.