Ecophysiological Studies on Water Storage and Water Stress in Tree Species

在突然停止灌溉造成的严重干旱胁迫下，锯齿栎和香樟的光合速率和蒸腾速率对环境条件的变化没有表现出任何响应。另一方面，几个树种幼苗的物候和生理反应克服了弱干旱胁迫。尤其是水分胁迫程度越大，叶片的生理响应越快。以日本柳杉、钝头山茱萸、柳叶木兰和锯缘栎4种大树为研究对象，在黎明前进行采伐，用称重传感器将其整个顶部悬挂起来，测定其总重量的变化。同时，水从树干的横截面供应。采用热脉冲法测定了树干切段液流速度（HPV：Heat Pulse Velocity）的变化。在切茎后不久，由于切茎和供水解除了木质部的负压，日本石楠、钝叶石楠和柳叶石楠的HPV（HPVpul）出现了突然的、试探性的增加。而锯缘青冈的HPV感染率没有明显的上升，日本青冈和钝齿青冈的HPV感染率分别在1.5和2.5小时后恢复到正常水平。而柳叶忍冬在切顶后1 h内，其水分供应能力就消失了，说明柳叶忍冬比日本忍冬和钝叶忍冬更容易供水。这意味着针叶树种的管胞系统比环孔木质部的导管系统具有更高的水流阻力。随着离树干深度的增加，HPVpul与日最大HPVmax的比值逐渐增大，在18 mm处超过1，说明断顶前的HPVmax并不代表最大导水能力。

Rate of photosynthesis and transpiration of Q.serrate and Cinnamomum Camphora could not show any response to the changes in environmental conditions under severe drought stress cause by the sudden cessation of irrigation. On the other hand, long by weak drought stress was conquered by the phenological and physiological response of seedlings of several tree species. Especially the greater the degree of water stress was, the faster the physiological response of leaves occurred. Four big tree species (Cryptomeria japonica, Chamaecyparis obtusa, Magnolia salicifolia and Quercus serrata) were cut before the dawn and whole top part were hung by load-cell to measure the changes in total weight. At the same time, water supplied from the cross section of the trunk. Heat pulse method was used to monitor the changes in sap flow velocity (HPV : heat pulse velocity) by the cut of stem. Just after the cut of stem, C.japonica, C.obtusa and M.salicifolia showed a sudden and tentative increase in HPV (HPVpul), because the negative pressure in xylem was dissolved by stem cutting and water supply. Q.serrata, however, did not show such a sudden increase in HPV.The HPVpul of C.japonica and C.obtusa returned to the normal level after 1.5 and 2.5 hours, respectively. On the other hand, that of M.salicifolia disappeared after only one hour from the top severance, indicating that M.salicifolia could supply water easier than C.japonica and C.obtusa. It means that a tracheid system in coniferous species has higher resistance to water flow in a tree trunk than a vessel system in ring porous xylem. The ratio of HPVpul to the daily maximum HPV of C.japonica increased with the depth from the trunk and it exceeded unity at 18 mm depth, which means HPVmax before the top severance did not represent the maximum capacity of water conductance.