Effects of nitrogen forms on transport and accumulation of ions in canola (B. napus L.) and rice (Oryza sativa L.) under saline stress

【Objectives】 Soil salinization is one of the main factors restricting crop yields, salt stress adversely impacts nutrient transport and distribution, resulting in nutrition imbalance and tunted plants, seriously threatens the countrys food production. Nitrogen is the largestdemand element for plant growth, NO-3 and NH+4 are the two nitrogen ionic forms plants absorberd.The study of ammonium and nitrate influences on plant growing and salt tolerance under salt stress is of great significance for improving plant salt tolerance and yield. 【Methods】 Canola (Brassica napus L.) and rice (Oryza sativa L.) were used as experimental material, and hydroponic experiments were conducted to investigate the effects of NO-3 and NH+4 and salt stress on canola and rice seedlings growth, Na+ accumulation in different organs, Na+ concentration in xylem sap and phloem exudates. 【Results】 1)Root growths of canola and rice were significantly promoted by nitrate nutrition under non-stressed conditions. Biomasses of canola and rice were significantly decreased under salt stress, and the decrease supplied with ammonium was significantly larger when than with nitrate. 2)Na+ contents in canola and rice seedlings were markedly increased under nutrition supply with both nitrate and ammonium nutrition under salt stress. In canola, the Na+ content in petiole of plants was significantly higher when supplied with nitrate than with ammonium nutrition, the Na+petiole/ Na+blade of canola seedlings was greaterwhen supplied with nitrate than with ammonium. In rice, the Na+ content in the roots of plants supplied with nitrate was significantly lower than that with ammonium nutrition, whereas the opposite trend was found in the shoots. 3)Na+ injury efficiency of canola and rice seedlings supplied with nitrate was greater than that with ammonium nutrition. 4)The K+ absorption capacity ofNO-3-N +NaCl in canola shoot and rice root was greater than those with ammonium nutrition. 5)Na+ concentration in xylem sap, Na+ and K+ concentration in phloem exudates of canola and rice seedlings supplied with nitrate were significantly higher than that with ammonium nutrition under salt stress. 【Conclusions】Compared with ammonium nutrition, canola and rice seedlings supplied with nitrate nutrition has higher salt tolerance. In canola, the Na+ content in petiole of plants supplied with nitrate is significantly higher than that with ammonium nutrition, indicating that the petiole of canola seedlings fed with nitrate plays greater role in retention Na+ than that did with ammonium. Nitrate nutrition is more conducive to absorb K+, helps plants to maintain the ion homeostasis. Canola and rice seedlings supplied with nitrate nutrition has stronger ability of ion regulatory in xylem-phloem, which is one of the reasons of higher salt tolerance than the ammonium salt nutrition.