Effects of nitrate on the root growth and salt tolerance of Suaeda physophora seedlings under NaCl stress

Effects of NaCl and nitrate on the root morphologic characteristics and nitrogen accumulation in the shoot of Suaeda physophora seedlings were investigated in order to elucidate the relationship between nitrogen and salt tolerance. S. physophora seedlings were grown under four NaCl levels (1, 150, 300 or 450 mmol/L) and three NO3--N levels (0.05, 5 or 10 mmol/L) making twelve combination treatments. The results showed that the dry weight, lateral root length, surface area, absorbing area and active absorbing area of root of S. physophora seedlings increased with an increase in salinity or nitrate level. Meanwhile, ions and nitrogen accumulation in shoot had significantly positive correlations with those root morphologic characteristics. Increasing of nitrate levels in the high NaCl solution increased the Na+, NO3-, organic nitrogen concentrations and nitrate reductase activities, while decreased Cl- and K+ concentrations. Positive response of S. physophora seedlings under high NaCl stress could be attributed to N application which increased root growth and improved Na+ and nitrogen accumulation in the shoot of seedlings. Contribution of nitrate and Na+ to osmotic adjustment increased and nitrogen nutrient deficiency was ameliorated, and hence the tolerance to high NaCl was enhanced.