Water movement and characteristics of dry resistance of tree species in a system of soil-trees

(1)采用附着分支真空提取法，研究了11年生水木（Mizuki）分支木质部汁液中主要无机离子夜间浓度的季节变化。有增加，大多数离子的浓度只是在叶紧急随后迅速下降，因为叶片扩大。晴天时，分支木质部汁液中无机离子浓度中午最高，高处最低。分支木质部汁液取样调查养分浓度时，需要考虑取样时间和取样持续时间。(2)为探明城市公园主要树种（水杉、水杉、奇亚木、白柿）的水分胁迫特征，测定了其叶片木质部压力势（XPP）的日变化和季节变化。无论晴天还是阴天，树冠下部的XPP值都是相同的。降水量多的年份白市夜间XPP明显偏高。在白天。夏季，白市和基亚基的XPP随降水量的增加而增加。结果表明，川明和白柿的蒸腾阻力大于水杉和红杉树。(3)以水原和庆明的扦插苗为材料，研究了前期土壤水分降低对XPP恢复的影响。土壤干燥处理后，幼苗对水分胁迫的抗性似乎随着处理的严重程度而增加，即使是在一定的持续时间内。

(1) The seasonal variatios of the nocturnal concentrations of the major inorganic ions in the branch xylem sap of 11-year-old Mizuki was studied by vacuum extraction using an attached branch. There were increase in the concentrations of most ions just prior to leaf emergency followed by rapid decreases as the leaves expanded. On a clear summer day, the inorganic ion concentrations of branch xylem sap were maximum at noon and minimum at hight. The time and duration of sampling need to be considered when sampling branch xylem sap in investigating nutrient concentration.(2) Daily and seasonal changes of the xylem pressure potential (XPP) of foliage were measured to clarify the characteristics of water stress of some major trees (Iatsura, Metasequoia, Keyaki, Shirakashi) in an urban park. XPP values of the lower part of the crown were the same regardless of weather it was sunny or cloudy weather. XPP of Shirakashi during the night was obviously high in year of large amounts of precipitation. During the daytime. XPP of Shirakashi and Keyaki increased with precipitation during the summer. The transpiration resistance of Keyaki and Shirakashi seemed to be higher than that of Katsura and Metasequoia.(3) The effects of previously reduced soil water content on the recovery of XPP were investigated using ptted seedling of Keyaki and Mizunara. Seedlng resistance to water stress after the soil drying treatment seemed to increase with the severity of the treatment even through it was of sort duration.