Effect of Different NO3-/NH4+ Ratios on Photosynthesis, Respiration and Antioxidant Enzymes Activity of Canola (Brassica napu L.) in Saline Condition

In order to study the effects of different N sources in different salinity levels on photosynthesis٫ respiration and antioxidant enzymes activity of canola a factorial experiment was conducted in a completely randomized design in East Azarbaijan Agricultural and Natural Resources Research Center glasshouse in 2008. The first factor was different sources of nitrogen including NO3-/NH4+ ratios (0:100, 25:75, 50:50 and 75:25) and the second factor was salinity as 0 and 200 mM NaCl. The highest fresh and dry weight, leaf area, relative water content, photosynthesis, respiration and leaf P was obtained at 50:50 NO3-/NH4+ ratio in non-saline condition. Increasing salinity decreased significantly all above characteristics. But it seems that 50:50 NO3-/NH4+ ratio decreased negative impacts of salinity injury to plant. Antioxidant enzymes activity was significantly higher in saline condition than control. The lower ratio of NO3-/NH4+ led to higher activity of these enzymes. The enzymes highest activity obtained atNO3-/NH4+ ratios as 50:50 and 25:75. It was concluded that canola can tolerate better salinity stress in presence of proper ratios of N sources