Effects Of Nitrogen On Physiological Characteristics Of Maize Under Drought Stress

1. Effects of drought stress on seed germination and seedling growth of maizeThe germination rate, germination potential, germination index, vigor index and drought index of maize seeds zhengdan958 all declined under the stress of mannitol?200, 400, 600 m M?. Mannitol stress not only reduced the germination rate of maize seeds, but also affected the germination speed and uniformity. The growth of maize seedlings was inhibited. The shoot fresh weight, root fresh weight, shoot length and root length of maize seedlings all delined with the increase of mannitol concentration. The effect of mannitol stress on shoot was more obvious than that on root, causing an increase of root-shoot ratio. The larger root-shoot ratio is beneficial to make full use of moisture and improve drought resistance of maize seedlings. Each index changed slightly under 200 m M mannitol treatment, but decreased significantly under 400 m M mannitol treatment. 2. Effects of nitrogen on seedling growth and physiological index of maize under drought stressThe leaf relative water content, shoot fresh and dry weight, root fresh weight, shoot height and leaf area of maize all decreased with the increase of drought degree, whlie root dry weight and root-shoot ratio increased first and then decreased. The appropriate nitrogen concentration could reduce the inhibition of drought stress on maize growth. The leaf relative water content, shoot and root fresh and dry weight, shoot height and leaf area of maize all increased with the increase of nitrogen concentration under the condition of normal growth and light drought stress. And the promoting effect of nitrogen on shoot was greater than root, leading to decline in root-shoot ratio. The effect was best at 7.5 m M nitrogen level and declined at 15 m M under severe drought stress.MDA, H₂O₂ and O₂-. accumulated in leaves of maize under drought stress and the appropriate nitrogen concentration could inhibit its accumulation. The MDA content, H₂O₂ content and O₂–. production rate in leaves of maize decreased with the increase of nitrogen concentration under the normal growth and light drought stress. While they declined first and then increased under severe drought stress. However, excessive nitrogen concentration did not have very good inhibitory effect on accumulation of active oxygen, but decreased the inhibitory ability.The activity of SOD, CAT and APX in leaves of maize increased under light drought stress while decreased significantly under severe drought stress. Appropriate nitrogen concentration could increase the activity of SOD, CAT and APX. The activity of SOD, CAT and APX in leaves of maize were positively correlated with nitrogen concentration under the normal growth and light drought stress. Under severe drought stress, enzyme activity was the highest when nitrogen concentration was 7.5 m M, while decreased under 15 m M nitrogen treatment.The NO₃- content and NR activity in leaves of maize decreased significantly under drought stress. Appropriate nitrogen concentration could increase NO₃- content and NR activity in leaves. The NO₃- content and NR activity in leaves of maize increased with the increase of nitrogen concentration under the condition of normal growth and light drought stress. While the NO₃- content and NR activity increased first and then decreased under severe drought stress. However, excessive nitrogen concentration inhibited the NO₃- content and NR activity.The soluble protein content in leaves of maize increased first and then decreased with the increase of drought degree. While proline content decreased continually. The appropriate nitrogen concentration could help the accumulation of soluble protein and proline in leaves. The soluble protein and proline content in leaves of maize were positively correlated with nitrogen concentration under the normal growth and light drought stress. Under severe drought stress, There were no obvious change between the 7.5 m M and 15 m M nitrogen treatment.The ABA content in leaves of maize increased significantly and was positively correlated with nitrogen concentration under drought stress. The results showed that the appropriate nitrogen concentration helped plants to resist drought stress. While too high or too low concentration of the nitrogen would increase the sensitivity of maize to drought stress. 3. Effects of nitrogen on photosynthetic characteristics of maize seedling under drought stressThe content of chlorophyll a and b, net photosynthetic rate?Pn?, transpiration rate?Tr?, stomatal conductance?Gs?, the maximum photochemical efficiency?Fv/Fm? and actual photochemical efficiency??PSII? in leaves of maize all decreased under drought stress. Whlie intercellular CO₂ concentration?Ci? deccreased first and then increased. The appropriate nitrogen concentration could increase the photosynthetic capacity of maize. Under the normal growth and light drought stress, the chlorophyll content, net photosynthetic rate?Pn?, transpiration rate?Tr?, stomatal conductance?Gs?, the maximum photochemical efficiency?Fv/Fm? and actual photochemical efficiency??PSII? in leaves of maize increased with the increase of nitrogen concentration. Under severe drought stress, they showed a downward trend after rising first. The excessive nitrogen concentration weakened the photosynthetic capacity of maize. The intercellular CO₂ concentration?Ci? decreased with the increase of nitrogen concentration.