中文摘要：

目前尾巨桉（Eucalyptus urophylla×E.grandis）在南部大面积种植,尤其是在广西,其水分利用效率对森林可持续发展和水资源管理的影响越来越受到关注,因此了解其水分利用特征具有一定的意义。该文通过Granier热扩散探针法（TDP）对广西黄冕国有林场4-5年生尾巨桉人工林液流密度（SFD）的年变化规律、不同个体变化及其与环境因子的关系进行了研究。结果表明：尾巨桉年平均日液流密度为830.1 L·m-2·d-1;从尾巨桉日液流密度的年变化来看,最大值不超过2 000 L·m-2·d-1,与相似研究比较,该研究得到的结果偏低。不同直径尾巨桉SFD具有相似的变化趋势,胸径相近其液流密度也大致相同,但胸径相差很大时,其液流密度相差也大,相差最大可达1 300 L·m-2·d-1,这主要与不同生长状况的植物根系从土壤吸收水分能力不同有关。相关研究表明光合有效辐射和水汽压亏缺是树木冠层蒸腾的主要动力,该研究也发现树干液流密度与水汽压亏缺（VPD）、光合有效辐射（PAR）在年变化上有很好的同步性,主要表现出夏秋季节较高、春冬季节较低的现象。SFD与PAR的关系比较显著,与VPD、空气温度（AT）、土壤温度（ST）有一定的关系,但与空气相对湿度（RH）和土壤湿度（SM）没有呈现规律。环境因子和植物生物学特征是树干液流密度主要的影响因素,进一步探讨尾巨桉如何响应这些因子的变化显得尤为重要。

英文摘要：

Large number of Eucalyptus urophylla × E. grandis plantations have been planted in the southern area of China,especially in Guangxi Zhuang Autonomous Region in the recent years. The influence of water use efficiency in sustainable forest development and water resources management has been receiving increasing attention. Therefore,under-standing the water use characteristics is important. The Granier thermal dissipation probe method（ TDP） is commonly used to monitor tree trunk flow. The sap flow density（ SFD） was monitored in four years E. urophylla × E. grandis plantation for one and a half years by Granier TDP at Guangxi Huangmian forest. The change in regularity of SFD,the SFD in trees of different diameters at breast height and the relationship between the SFD and the environmental factors were studied. The results showed that average daily SFD was 830.1 L·m-2·d-1,and the maximum value did not exceed2 000 L·m-2·d-1,when compared with similar studies,these results were relatively low. Because tree trunk was the main part of the plant for water transport,it was necessary to analyze the tree trunk sap flow density（ SFD） change at about different diameters at breast height of E. urophylla × E. grandis. There was a positive correlation between SFD and diameter. The SFD was similar when the DBH（ diameter at breast height） were in the same diameter class. The SFD varied from tree to tree with different values of maximum and minimum SFD（ 1 300 L·m-2·d-1at most）. This was mainly caused by the different water absorbing capacities of trees. Many studies showed that photosynthetic active radiation and vapor pressure deficit（ VPD） were the main factors of tree canopy transpiration. The SFD and VPD,photosynthetic active radiation（ PAR） displayed similar trend over the study period and exhibited a unimodal curve. The value of SFD was higher in summer and fall,and lower in spring and winter. The relation between SFD and PAR showed significant difference,and there was relation between SFD a