| In this experiment, the Fraxinus mandshurica seedlings in eastern Liaoning province as the research object. To create a low-temperature environment by simulating the natural cooling and make use of low temperature and duration, low temperature and different light interaction methods for the seedlings’s experimental control process. Following by measuring and analysising physiological indexes, photosynthetic characteristics and fluorescence characteristics discussion on the defense mechanisms and damage mechanism the seedlings to low temperature. From the physiological and ecological point of view discussed different low temperature stress at different durations and different coupling low light conditions at low temperature. To provide a scientific basis for the study of cold resistance and the introduction and cultivation of Fraxinus mandschurica. Specific results as follows:1.The seedlings’s relative conductivity,malondialdehyde (MDA) and superoxide dismutase (SOD) content under different low temperature treatments significantly different or significantly (p<0.01; p<0.05; p<0.01). As the temperature dropped, the seedlings relative conductivity, MDA content gradually increased, SOD were rising slowly at first, then gradually declining. This indicates that as the temperature decreases seedling tissue was gradually damaged, cell wall was gradually destroyed. In the initial stages of hypothermia drop the seedlings may get some cold acclimation, there will be some increase of cold hardiness. In the initial stages of low-temperature drop(>-4℃) the seedlings may get some cold acclimation, there will be some increase to cold hardiness. But when the temperature continues to drop(<-4℃), membrane permeability increased, membrane systems were severely damaged, the plant would suffer serious harm or even death.2.To maintain-4℃) temperature threshold constant, the seedlings’s relative conductivity,malondialdehyde (MDA) and superoxide dismutase (SOD) content under different low temperature treatments significantly different or significantly (p<0.01; p<0.01; p<0.05). With the extend of low-temperature duration, the seedlings’s relative conductivity and,malondialdehyde (MDA) increased significantly after the first rise slightly, SOD activity increased first and then tended to decrease. Which shows that low temperature stress in the early stages of the seedlings through self-regulation mechanisms to adapt to stress, reduce the damage caused by low temperature, with the extension of stress time, osmotic adjustment and antioxidant enzyme membrane system and regulatory mechanisms of the protective effect beyond a certain limit, it will result in metabolic disorders, causing irreversible damage.3. Seedlings relative conductivity, MDA and SOD content at different temperatures, light and their interaction were significantly different (p<0.01). Under different lighting conditions, the seedlings’s relative conductivity,malondialdehyde (MDA) and superoxide dismutase (SOD) content with decreasing temperature gradually increased. At the same temperature, the relative conductivity and MDA content higher in the T1 and T3 radiation than T2 of the seedlings. SOD change just the opposite. This shows that compared with the normal temperature, light intensity is too high or too low will affect the growth and development of plants, but the interaction of high light with low temperature far greater than the damage caused by low temperature and low light interaction.4. From the view of changes in the indicators from the interaction of different temperatures and light on Photosynthesis and plant seedlings characteristic parameters, At the process of low temperature stress, the Pn and LSP lower in the T1(1200μmol·m-2·s-1) and T3(80μmol·m-2·s-1) radiation than T2(500μmol·m-2·s-1) of the seedlings. LCP changes just the opposite. Especially in-2℃ with high-light and low-light interaction is minimized. This indicates that after low temperature stress high-light and low-light on the seedlings have a certain degree of damage, has played the role of inhibition of photosynthesis. AQY,Am,Rd same with Pn and LSP. Which shows that plants’s photosynthetic apparatus and performance will be damaged at lower temperatures, so that the adaptability and ability of plants to light and weaken will be reduced, and maintain their own life activities consume organic matter less and less, low temperature under high light conditions injury largest plant photosynthetic apparatus.5. As the temperature decreases, three values of Fv/Fm under different illumination levels showed a downward trend. At the same low temperature conditions, Fv/Fm values with different light intensities and different, among the largest Fv/Fm isT2(500μmol·m-2·s-1), T3(80μmol·m-2·s-1) secondly, T1(1200μmol·m-2·s-1) minimum. Under three different illumination levels,qP,ETR,as the temperature decreases both showed a clear downward trend, among qP maximum value under the lighting conditions. qP values T1 lighting conditions are greater than the value qP change T3 and T2. At the same low temperature conditions, ETR value under three different lighting conditions are not the same, among ETR at T2 maximum value. Description above parameters change, optical system Ⅱ under low-temperature and high light interaction by the most serious injury. It showed that low-temperature and high light interaction cause greater degree of Cold-sensitive plant damage. |
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