中文摘要：

应用Granier热扩散技术对内蒙古浑善达克沙地榆（Ulmus pumila var．sabulosa）疏林林分进行树干液流通量研究。选择该区占林分80％以上林木的3种胸径级（小径级，15—25cm；中等径级，25-35cm；大径级，〉35cm）榆树，使用Granier探针进行每隔15min的树干液流测定。同步测定各林分环境因子。林分中不同胸径级榆树树干液流通量特征表现为：树干液流密度峰值大径级树〉中等径级树〉小径级树。且差异明显；大径级树由于林龄较大，液流密度曲线变化平缓，没有明显的峰值。呈弧形曲线；液流密度随季节推移在生长季中液流密度均值逐渐减小，在生长季末期（10月）基本处于微弱波动状态。液流通量最大月平均值一般出现在6—8月。不同径级树月液流通量变化差异较大。对样木的日液流通量比较发现，胸径对液流有显著影响。对不同胸径树木各树种影响较大的环境因子为饱和水汽压差（VPD），光合有效辐射（PAR）。气温（Ta）；在不同生长季节。对不同胸径类型树木起主要作用的环婧因子也不尽相同．但是PAR和VPD是其中起主要作用的两个因子。

英文摘要：

Sap flux density of Ulmus pumila var. sabulosa in typical elms sparse forest in Hunshandake Sandland of Inner Mongolia was studied by using Granier technology. Nine dominant trees with different Diameters at Breast Height （DBH） which belong to three classes of DBH, that is, 15-25cm （small DBH）, 25-35cm （medium DBH） and 〉35cm （large DBH）, respectively in natural forest were selected and measured in terms of sap flux density. At the same time, various environmental factors including air temperature, relative humidity, photosynthetically active radiation, and wind speed were monitored in the whole growing season. The sap flow characteristics of forest stand are： sap flow density peak value of large DBH is larger than that of medium DBH tree and then small DBH tree. Sap flow density of large DBH trees change gently because age of stand. Average monthly sap flow density is less with the shift of growing season; the sap flow density enters into the state of weakly fluctuation in the end of growing season （October）. The maximum value of average monthly sap flow density for varied tree species appears from June to August, the differences among dominant, medium and small trees are large. The main influence environmental factors are VPD, PAR, Ta. At different months, the dominant environmental factors have changed, but the two main factors are PAR and VPD.