Physilogical Responses Of Canola (Brassica Napus L.) And Rice (Oryza Sativa L.) To Salinity Under Different Nitrogen Forms By

Soil salinization is one of the main factors restricting crop yields, salt stress adverse impact on nutrient transport and distribution, resulting in nutrition imbalance and tunted plants. The saline-alkali soil areas continue to expand, so that our arable land declining, serious threatens the country’s food production. Nitrogen is the largest element of plant demand, and is considered as a major limiting factor for plant growth, NO3- and NH4+ are two nitrogen ionic forms which plants absorb. Therefore, the study of ammonium and nitrate influence plants growing and salt tolerance under salt stress is great significance. In this paper, canola (Brassica napus L.) and rice(Oryza sativa L.) were supplied as experimental material, and hydroponic experiments were conducted to investigate the effects of nitrogen forms (NO3- and NH4+) and salt stress on canola and rice seedlings growth, water relations, photosynthesis, Na+ accumulated in different organs, Na+ concentration in xylem sap and phloem exudates, and Na+ distribution in leaf apoplast and symplast, which can illustrate the response of canola and rice supplied with different nitrogen forms under saline condition, and the two crops salt tolerant mechanisms. The main results are as follows: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 after salt stress, and the decrease in biomass from the plants supplied with ammonium was significantly inhibited compared to that in the plants supplied with nitrate.2. Salt stress significantly reduced the leaf water potential, and the the leaf water potential of canola grown with nitrate was higher than that with ammonium. Osmotic stress was greater in canola seedlings supplied with ammol/Lonium. Whlie there was no significant difference in leaf water potential between with rice supplied with nitrate and ammol/Lonium.3. The reduction of net photosynthetic rate, stomatal conductance and intercellular CO2 concentration were greater in A+NaCl treatment canola seedlings than N+NaCl plants. Compared with the control, salt stress significantly reduced stomatal conductance nutrition intercellular CO2 concentration of rice with ammonium supply, while had no significant negative effects in nitrate nutrition of rice. Therefore, canola and rice with nitrate nutrition had better photosynthesis.4. 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 supplied with nitrate was significantly higher than that with ammonium nutrition, the [Na+] petiole/[Na+]blade of canola seedlings supplied with nitrate was greater than that with ammonium nutrition, indicating that the petiole of canola seedlings fed with nitrate played a greater role in retenting Na+ than that did in ammonium. We found that plants supplied with nitrate nutrition were more resistant to salt stress compared with ammonium nutrition by calculating Na+ injury efficiency. The K+ absorption capacity of NO3--N+NaCl canola and rice was greater than that with ammonium nutrition; it helped to maintain the plants ion homeostasis.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. And Na+ content in leaf apoplast and [Na+]sym/[Na+]apo of canola and rice seedlings with nitrate nutrition was higer than that with ammonium. Therefor, canola and rice with nitrate nutrition has stronger ability of ion regulatory in xylem-phloem and Na+ compartmentalization in the leaf apoplast probable was the reason why canola and rice seedlings with nitrate nutrition is more resistant to salt stress.