The Ecophysiological Response Of Podocarpus Fleuryi Hickel Seedlings To Low Temperature Stress

To study the ecophysiological effects of low temperature stress on podocarpus fleuryi Hickel seedlings, two-year-old seedlings were selected as experimental material. We conducted comparative study. On the one hand, seedlings were separately placed in the plots located at the top, half-way-up and the foot of Jinyun Mountain (different altitudes at Jinyun Mountain led to the difference in air temperature) and subjected to winter low temperature stress. On the other hand, in laboratory, seedlings were exposed to simulated low temperature (above and below zero degrees) stress which were artificially controlled .We studied the water content, photosynthesis, damage of cell membrane and osmoregulation of seedlings' leaves, and analyzed some ecophysiological indexes including MDA, electrolytic permeability, activities of SOD, CAT and POD, and contents of water, pigments, soluble sugars, protein and free prolin in leaves. Their variations with time were determined and analyzed in order to explore the ecophysiological response of podocarpus fleuryi Hickel seedlings to low temperature stress.It was shown that the total content of water in leaves changed little, but the content of bound water increased and the content of free water decreased, which resulted in an obvious increase in the ratio of bound water/free water. These results indicated that podocarpus fleuryi Hickel seedlings could adaptatively increase their bound water content to resist lowtemperature stress in winter. The contents of Chla and Car were sensitive to low temperature stress, it seems that they were vulnerable to low temperature stress and partly decomposed. Relatively, the content of Chlb changed little. The ratio of Chla/b had positive linear correlation with temperature, which meant the photosynthetic ability of podocarpus fleuryi Hickel seedlings declined under winter low temperature stress. With the drop of air temperature, the content of Car increased. This was due to its specific functions in plants.Under winter low temperature stress, the injury of membrane caused by membrane lipid peroxidation could occur in podocarpus fleuryi Hickel seedlings, even though it was not serious lipid peroxidation damaged the structure and function of cell membrane, and resulted in the increase in membrane electric conductivity, membrane permeability and electrolyte leakage. At the same time, the simulated low temperature stress showed the electrolytes could only leak largely when the temperature were extremely low or drops abruptly, that membrane lipid peroxidation were mitigated by some other factors during the period of winter low temperature stress. Taking the activities of SOD, CAT, POD and content of MDA (which was the product of membrane lipid peroxidation) into account, it could be concluded that light low temperature stress could not seriously damage membrane induced by membrane lipid peroxidation. This could be partly due to the coordination of SOD, CAT and POD. Only under the sudden strike of extremely low temperature, such as -10癈, -20 癈, the cell membrane could be seriously damaged by lipid peroxidation.The variations in the content of main metabolic osmoregulatory substances, such as soluble sugars, protein and free proline were all tightly related to the cold resistance of podocarpus fleuryi Hickel seedlings. However, the relations to cold resistance were not the same among these substances. The content of soluble sugars was affected by many factors and presented a complex variation pattern. The change in the content of free proline was sensitive to low temperature stress, podocarpus fleuryi Hickel seedlings could strengthen their cold resistance through accumulating free proline., Though the hardening of low temperature, podocarpus fleuryi Hickel seedlings could increase their contents of soluble protein and strengthen their adaptive capacity to low temperatures. Under simulated low temperature stress, the decrease in the content of soluble proteins indicated that the protein anabolism were hindered, specifically when freeze injury o...