Role of Ammonium and Nitrate as Nitrogen Source on Salt Tolerance in Nerium oleander L.

Abstract

The effect of ammonium and nitrate as nitrogen source on growth, water relation and ions concentration were studied in Nerium oleander L. under NaCl salinity. Plants were grown in semi automatic sand culture system in the greenhouse. It was revealed that salt tolerance of Nerium plants was significantly increased when supplemented with nitrate as sole nitrogen source than that of ammonium. Total dry weight, leaf area and number were reduced more drastically in ammonium than nitrate treated plants. A higher level of Na⁺ and Cl^- was observed in leaves and branches in ammonium treated plants under salinity whereas these ions were accumulated in roots in nitrate. Additionally, salinity induced more decrease in K⁺/Na⁺ selectivity and K⁺ concentration in leaves and branches of ammonium fed plants. Osmotic adjustment was done faster in nitrate treatment and leaves succulence ratio as weight per leaf area did not decrease due to salinity. Decrease in photosynthetic rate was almost similar in both nitrogen treatments under salinity. Our result indicates that nitrate fed plant reduced the level of stress by reducing concentration of Na⁺ and Cl^- in leaves. In contrast, sequestration and counterbalance of high concentration of Na+ and Cl^- in leaves of ammonium fed plants is highly energy required process and diverted the energy from plant production.