Abstract:The objectives of this experiment were to study the effects of CaCl2 concentration on N metabolism in roots, stems and leaves of sour jujube under NaCl stress and to determine the ability of exogenous Ca to alleviate NaCl stress in sour jujube seedlings. The jujube seedlings were used as test materials to measured hydrogen peroxide (H2O2) and super oxide (O-·2) concentrations in the leaves by different concentrations of CaCl2 (0, 5, 10 and 20 mmol/L) under NaCl stress (150 mmol/L). The activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthase (GOGAT) and the concentrations of free amino acid, protein and NO3N were measured in roots, stems, and leaves. Principal component analysis was used to select the best physiological indexes for evaluating the ability of CaCl2 to alleviate NaCl stress in sour jujube seedlings. The results showed that 5 and 10 mmol/L CaCl2 significantly reduced H2O2 and O-·2 concentrations in the leaves of NaClstressed sour jujube seedlings. The 5 and 10 mmol/L CaCl2 treatments significantly increased GOGAT activity in roots and stems. All of the CaCl2 treatments significantly increased GOGAT activity in leaves. Leaf GS and NR activities were significantly increased by all of the CaCl2 treatments. Root GS and NR activities were significantly increased by 10 and 20 mmol/L CaCl2, whereas 5 mmol/L CaCl2 had no significant effect. Stem GS and NR activities were increased only by 10 mmol/L CaCl2. All of the CaCl2 treatments significantly increased protein contents in roots, stems, and leaves. The 10 and 20 mmol/L CaCl2 treatments increased free amino acid contents in roots and stems, whereas only the 10 mmol/L CaCl2 treatment significantly increased free amino acids in leaves. The 10 mmol/L CaCl2 treatment significantly increased NO3N concentrations in roots and stems. All three CaCl2 treatments increased NO3N concentrations in leaves. The 150 mmol/L NaCl stress treatment caused significant peroxidative damage to wild jujube seedlings and inhibited N metabolism. Exogenous CaCl2 helped the sour jujube seedlings adapt to NaCl stress by promoting the assimilation of NH4+ via the GS/GOGAT cycle in roots and stems and by increasing NR activity and regulating NO3N transformation rates. The results showed that 10 mmol/L CaCl2 was the most effective treatment for alleviating NaCl stress in sour jujube seedlings. The GOGAT activity, NR activity, and free amino acid concentrations can be used to evaluate the ability of CaCl2 to alleviate NaCl stress in sour jujube.