Ecophysiological Studies on Water Storage and Water Stress in Tree Species

突然停止灌溉引起的严重干旱胁迫下，锯齿青树和樟树的光合作用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，几种树种幼苗的物候和生理反应克服了长期的弱干旱胁迫。尤其是水分胁迫程度越大，叶片的生理反应发生越快。黎明前砍伐四种大树种（柳杉、扁柏、厚朴和锯齿栎），并用称重传感器悬挂整个顶部以测量总重量的变化。同时，水从树干的横截面供给。采用热脉冲法监测茎切割后液流速度（HPV：热脉冲速度）的变化。茎切断后，C.japonica、C.obtusa 和 M.salicifolia 的 HPV (HPVpul) 出现突然的、暂时性的增加，这是由于茎切断和供水溶解了木质部的负压。然而，锯缘 Q.serrata 并没有表现出如此突然的 HPV 升高。 C.japonica 和 C.obtusa 的 HPVpul 分别在 1.5 和 2.5 小时后恢复到正常水平。另一方面，从顶部切断仅1小时后，柳叶就消失了，这表明柳叶比粳稻和钝叶柳更容易供水。这意味着针叶树种的管胞系统比环状多孔木质部的导管系统对树干中的水流具有更高的阻力。 HPVpul与粳稻日最大HPV的比值随着距离树干深度的增加而增大，在18mm深度处超过统一值，这说明顶断前的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.