The Study On Biological Effect Of Nitrogen Forms And Light Intensity On Cucumber Seedling Under Phenanthrene Stress

In an hydroponic experiment, the effects of different nitrogen forms (NO₃^--N and NH₄⁺-N) and light intensity (natural and low) on the growth, absorption of phenanthrene, N and P of cucumber seedlings were studied. The experiment clarified effect and mechanism of nitrogen forms and light intensity on cucumber seedling under phenanthrene stress from the aspect of photosynthesis characteristics (Pn, Gs, CE and AQY) of cucumber leaves. The results showed that:1. NH₄⁺-N nutrition enhanced the resistance of cucumber seedling to phenanthrene stress. Moderate phenanthrene stress (3mg/L) inhibited the growth of cucumber, but no lethal effect on cucumber seedling in short period. So that phenanthrene stress (3mg/L) is selected as critical concentration and used in the following experiments.2. Under phenanthrene stress(3mg/L), NH₄⁺-N nutrition enhanced slightly the tolerance to phenanthrene stress under low light condition. However, NH₄⁺-N nutrition significantly increased the tolerance of cucumber seedling to phenanthrene stress under nature light. It was evidenced that, low light reduced relatively the resistance of cucumber seedling to phenanthrene stress in NH₄⁺-N nutrition.3. Compared to NO₃^--N nutrition, NH₄⁺-N nutrition enhanced the resistance of cucumber seedling to phenanthrene stress. Firstly, although there were no diffenecces in phenanthrene content of cucumber seedling between NH₄⁺-N and NO₃^--N nutrition, inhibitory effect of phenanthrene on the growth of cucumber seedling is relative lower in NH₄⁺-N than in NO₃^--N nutrition. Secendly, NH₄⁺-N nutrition reduced the accumulation of phenanthrene in newly expanded leaves. Under natural light, phenanthrene content of newly expanded leaves is significantly higher in NO₃^--N than in NH₄⁺-N nutrition. Phenanthrene accumulation in newly expanded leaves up to 83.4ï¼…and 52.7ï¼…of total phenanthrene content in leaves and whole plants in NO₃^--N nutrition, respectively, while these distribution became 12.9ï¼…and 7.0ï¼…in NH₄⁺-N nutrition. These results implied that phenanthrene absorbed was accumulated mainly stored in stems in NH₄⁺-N nutrition, it was the primary mechanism to reduce the damage of photosynthesis organs of leaves. 4. Under NH₄⁺-N nutrition, seedlings maintained a higher relative Pn, CE and AQY. Inhibitory effect of phenanthrene on Pn, CE and AQY was lower NH₄⁺-N nutrition, while NO₃^--N nutrition showed a significant inhabitatory effect. NH₄⁺-N nutrition also enhanced the resistance of cucumber to low light intensity, whetrer phenanthrene stress was encountered or not, inhabitatory effect of low light on the growth of cucumber seedling was lower in NH₄⁺-N than in NO₃^--N nutrition. Low light and phenanthrene stress resulted in maintatining relative higher photosynthesis areas, photosynthesis rate, AQY and CE of cucumber seedling under NH₄⁺-N nutrition.