Response of canola seedlings to salt stress under different nitrogen forms

In order to study different nitrogen forms on the responses of canola plants to salt stress, the effects of the salt stress on growth, photosynthesis, and ions absorption and distribution of canola plants were investigated by supplying with ammonium and nitrate in nutrient solution. The results showed that the total dry mass and photosynthesis of canola plants supplied with nitrate and no NaCl was higher than those of the other treatments. Under the NaCl stress, there was a significant inhibition of growth of canola plants supplied with two nitrogen forms, but the inhibition was greater in canola plants supplied with ammonium than that supplied with nitrate. The inhibition of photosynthesis was mainly attributed to stomatal limitation in this experiment. Under the NaCl stress, there were significant increases of Na+ concentration in canola plants supplied with two nitrogen forms. In the leaf blades and petioles, the Na+ concentrations increased more sharply in canola plants supplied with ammonium than those supplied with nitrate. However, in roots, the greater increase was found in canola plants supplied with nitrate. Under the NaCl stress, the K+ concentrations in the whole plants and petioles declined remarkably supplied with two nitrogen forms. In roots, a significant decline of K+ concentration was found in canola plants supplied with nitrate, while the decline was not found in canola plants supplied with ammonium. Selectivity ratio of K+ and Na+ (SK,Na) in roots of canola plants supplied with ammonium was higher than that supplied with nitrate, while in petioles and the whole plants, SK,Na was higer in canola plants supplied with nitrate. To sum up, under the salt stress, the more salt tolerance of canola plants supplied with nitrate can be attributed to greater selectivity of K+ at whole plant level.