元宝枫苗木的水力结构特征

在温室条件下，控制不同干旱梯度，用改良的冲洗法测定了4年生元宝枫苗木的水力结构参数．研究表明，随着小枝水势的降低，水力结构各参数随茎段功能木质部直径的变化可以用不同的方程来模拟；导水率的大小受茎段所在区域的影响，限速区的导水率明显低于非限速区，限速区的存在对苗木个体的生存竞争有利．导水率、比导率和叶比导率都和功能木质部直径和小枝水势呈明显的正相关．较粗茎段的叶比导率远高于多次分枝的未端细小分枝，有利于苗木在干旱时保存那些光合积累较大的器官．在落叶之前，相同直径枝条的胡伯尔值随小枝水势的变化很小，说明苗木水分胁迫主要源于木质部空穴和栓塞．

Hydraulic characters of Acer truncatum seedlings

The hydraulic parameters of 4 years old Acer truncatum seedlings were measured by improved flushing method under the condition of controlled drought gradients in the greenhouse. It's indicated that the changes of hydraulic parameters with stem segment functional xylem diameter could be modeled by different equations. The hydraulic conductivity was influenced by the area that stem segment located. It was higher in non-constriction area than in constriction area. The existence of constriction area was in favor of the competition between individual seedlings. Hydraulic conductivity, specific conductivity and leaf specific conductivity were proportional with functional xylem diameter and twig water potential. The leaf specific conductivity of thicker branches was far higher than that of distal twigs, which was in favor of seedlings in saving those organs with more photosynthesis devotion during drought stress. The change of Huber value of same diameter branches with twig water potential was very small before defoliation, and hence, the main source of seedling's water stress came from xylem cavita-tion and embolism.