A Preliminary Study On The Cold Resistance Of Five Species Eucalyptus Seedling

The whole seedlings ( 90-100d ) of E.urophylla ,E.urophylla × E.camaldulensis , E.dunnii , E.grandis and E.urophylla ×temperature with RH was 75%-85%, illumination time was 8: 00-17: 00 and illumination intensity was 120mmol photons m^-2 s(-1) . The effect of low temperature stress on physiology and biochemistry of the five species were tested. And'the cold-resistance of the five species Eucalyptus were evaluated synthetically according to .these physiology and biochemistry index. The experiment set five different temperature treatments with artificial freezing method: 9±1℃, 6±1℃, 3±1℃,0±1℃,and-3±1℃, and the control was normal temperature.The main results are given as follows:1. The membrane permeability change of different species Eucalyptus had significant differences with temperature reducing. The relative conductance rate of five species Eucalyptus had a increasing trend with temperature decreased. Early low temperature (9～℃),decrease of the temperature ,the relative conductance rate increased gradually. When the temperature.was continue reduced (0～3℃) , the relative conductance rate increased significantly. The relative conductance rate of different Eucalyptus appeared reducing phenomena under different temperature, which showed that Eucalyptus maybe have prevention reaction to low temperature stress to renovate cell membrane during early period of temperature reducing. But with temperature continue reducing (0～3℃) , the relative conductance rate increased significantly, cell membrane were more damaged. When exposed to the low temperature of -3℃, except E.dunnii and E.urophylla ×E.camaldulensis the relative conductance rate of other Eucalyptus all were higher than 50%,which show that the absolutely mostly electrolyte in cell were lost and the leaves were damaged gravely under these low temperature. And the experiment showed that parts of leaves of E.urophylla and E.urophylla × E.grandis appeared to be water logging under -3℃.2. Low temperature have significant effect on physiology and biochemistry index of Eucalyptus. Under low temperature stress, the contents of soluble protein and the free proline dramatically changed. As a whole, the content of protein decreased with the decreasing of low temperature. Compared with the control, the content of free proline were increased under low temperature. The soluble sugar also were enhanced under low temperature, but during 0～3℃of soluble sugar was related to the cold-hardiness of Eucalyptus.3. Low temperature have significant effect on metabolize index ofEucalyptus seedling. The activity of SOD showed the trend of declining-rising-declining with the decreasing of low temperature, but as a whole, SOD activity was falling. The content of MDA increased with the decrease of temperature, which indicated that the membrane lipid peroxidization was enhanced under low temperature.4. The cold resistance of five species Eucalyptuses were evaluated by using principal component analysis. And the results showed that: the order of cold-resistance was E.urophylla × E.camaldulensis > E.urophylla >E.dunnii>E.grandis>E.urophylla × E.grandis.