Studies On Stress-resistance Of Four Introduced Oaks Seedlings

Quercus sp. has strong adaptability and is of high value in landscaping. But studies on stress-resistance are scarce. It is of practical significance to enrich plantation tree species of our country by researching the inverse-resistance of oak trees.The annual seedling of four oak trees(Quercus nuttallii, Quercus palustris, Quercus shumardii, Quercus bicolor) were used as materials to measure the changes of physiological and biochemical indexes(growth, the relative conductivity, POD, SOD, soluble protein, MDA content) under different gradients of salt stress(CK?0.1%?0.3%?0.5%?0.7%) by pot experiment in this paper, measure 4 times, with a frequence of once a week,in order to study the salt resistance of the four oak trees under different gradients of salt stress and time length. Dormant branches of four oak trees(Quercus nuttallii, Quercus palustris, Quercus shumardii, Quercus bicolor) were used as materials to measure the changes of physiological and biochemical indexes(the electrolyte leakage, POD, SOD, soluble protein, MDA content) under different low temperature conditions(0 ??-5 ??-10 ??-15 ??-20 ??-25 ??-30 ??-35 ?) in this paper. Logistic equation was applied to fitting change rules of the electrolyte leakage. The major research results were summarized as follows:(1)With the increase of salinity concentration and the extension of time,the height growth and diameter growth of the four oak trees decreased to different extents while the relative conductivity increased significantly. The order of the maximum relative conductivity is Quercus bicolor> Quercus shumardii> Quercus nuttallii> Quercus palustris. With the extension of time, the activities of SOD fluctuated first with some increase and then decrease and final increase. The order of the two peaks is: Quercus palustris>Quercus nuttallii>Quercus bicolor>Quercus shumardii. The activities of POD of the four oak trees increased in the early stage. Subsequently Quercus bicolor and Quercus shumardii decreased in different time periods(14d ? 21d). The order of the peak of POD is : Quercus palustris>Quercus nuttallii>Quercus bicolor>Quercus shumardii. With the increase of salinity concentration and the extension of time, the content of MDA increased significantly. The order of the maximum MDA content is : Quercus bicolor>Quercus shumardii> Quercus nuttallii> Quercus palustris. With the increase of salinity concentration, the soluble protein content increased significantly. However, with the extension of time, the soluble protein content increased and then decreased. All of the four species achieved the maximum on the 21 d. The order of the peak is : Quercus palustris>Quercus nuttallii>>Quercus shumardii Quercus bicolor. The salt resistance of the four oak trees is as follows : Quercus nuttallii >Quercus palustris> Quercus shumardii> Quercus bicolor.(2) The fitting effect was remarkable and correlation coefficient were all above 0.90. Semi-lethal temperature(LT50)of four kinds of oak trees were obtained by parameters analysis: Quercus palustris(-27.89 ?) > Quercus nuttallii(-25.11 ?) > Quercus bicolor(-24.78 ?)> Quercus shumardii(-22.42 ?). With the decrease of temperature, the trend of the soluble protein content increased and then decreased, the activities of POD and the amplitude of increase: Quercus palustris> Quercus bicolor> Quercus shumardii> Quercus nuttallii. The POD activities of the four oak trees decreased rapidly under the temperature of-20 ?.With the decrease of temperature, both of the activities of SOD and the MDA content increased and then decreased. But the amplitude of increase and decrease is different significantly between species. The amplitude of increase of soluble protein content: Quercus palustris>Quercus nuttallii>Quercus bicolor>Quercus shumardii. To sum up, the cold resistance of the four oak trees is as follows : Quercus palustris> Quercus shumardii> Quercus bicolor> Quercus nuttallii.