Biological Response of Capparis spinosa L. to Nitrogen Application under Salinity Conditions

Salinity stress is one of the major abiotic stresses, which reduces plant growth by reducing water absorption and disrupting the balance of nutrients. To study the effect of nitrogen fertilizer on the physiological traits of Capparis spinosa L. at high salt concentrations, a greenhouse experiment was conducted in a factorial arrangement based on a randomized complete block with three replications in 2022. The first factor included 5 levels of salinity (100 (control), 200, 300, 400, and 500 mM), and the second factor comprised 4 levels of nitrogen fertilizer (50, 100, 150, and 200 ppm). The traits under study included shoot dry weight, proline content, soluble sugar, malondialdehyde enzyme activity, and catalase. Results showed that quantum yield, proline content, and soluble carbohydrate were affected by salinity and nitrogen concentrations. With increasing salinity levels from 100 to 500 mM, proline and soluble carbohydrate content increased, but with increasing nitrogen levels from 50 ppm to 200 ppm, soluble carbohydrates and proline content decreased and increased, respectively. Shoot dry weight and catalase activity 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 content decreased while catalase, and peroxidase activity and shoot sodium content increased. According to these results, application of 200 ppm nitrogen is recommended in low (100 and 200 mM) and medium (300 mM) salinity levels while in high salinity (400 and 500 mM) levels, application of 50 ppm nitrogen in the nutrient solution of Capparis is recommended.