三种榆树幼苗对水分胁迫的生理响应

Physiological Responses of Three Elm Species Seedlings to Water Stresses

在人工模拟干旱的条件下,研究了自美国引种培育的岩榆、南方岩榆和国产白榆1 a生幼苗的叶片相对含水量(RWC)、电导率和叶绿素含量的变化情况,同时调查水分胁迫后期幼苗的存活率。结果表明:水分胁迫初期,3种榆树幼苗的叶片RWC、质膜透性、叶绿素a、叶绿素b及叶绿素总量均呈增加趋势;水分胁迫中期(第24天)白榆、南方岩榆的叶绿素总量呈现最大值,后开始缓慢下降,而岩榆仍继续上升至第30天后才开始下降,但各种幼苗叶片叶绿素a/b均增加。自然干旱初中期的RWC下降缓慢,后期失水迅速,白榆失水速率明显快于岩榆、南方岩榆。水分胁迫后期白榆叶片出现萎蔫,叶缘叶尖枯黄均早于南方岩榆、岩榆,萎蔫枯黄总数也最多,其次分别是南方岩榆、岩榆。因此,岩榆最耐干旱,南方岩榆次之,白榆较不耐旱。

Under the simulated drought conditions, the relative water content, chlorophyll （ chl ） content, electric conductivity in leaves of one-year-old seedling of Ulmus thomasii, U. Crassifolia and U. pumila were studied and the survival rate of seedlings was investigated in this paper. The results showed that at the period of slight water stress the relative water content, membrane permeability and chlorophyll content in leaves of three species were increased with water stresses. The contents of total chlorophyll in leaves of U. pumila and U. Crassifolia were highest at the middle period of stress （24 d after stress） and then began to decrease, while for Ulmus thomasii, its content lasted increase until 30 d after water stress. The ratio of chlorophyll a to chlorophyll b was increased for all three species. At the late period of experiment in which water stresses were severe, water content in the leaves of U. Crassifolia was lost obviously faster than that in Ulmus thomasii and U. pumila, and the chlorosis and wither leaves of U. Crassifolia were observed earlier and more than that of Ulmus thomasii and U. pumila. All the results indicated that U. thomasii was the most tolerant to drought, and U. pumila was least tolerant to drought among three species.