中文摘要：

使用热扩散探针法（TDP）监测黄土丘陵区2015年7—9月人工林中油松和沙棘树干液流密度（Js）的动态变化,并通过植物的水分利用生理特征判断2个树种的水分利用类型.结果表明：油松和沙棘的Js在降水前后均表现为单峰型日变化特征,油松生长旺盛期的Js（12.62 m L·m-2·s-1）显著高于沙棘（2.60 m L·m-2·s-1）.2个树种Js与光合有效辐射、水蒸汽压差、土壤体积含水量（SWC）呈显著正相关.8月和9月降水前后,2个树种的Js都主要受气象因素影响.9月降水导致SWC对沙棘Js的解释量增加4.2%,而8月和9月的降水导致SWC对油松Js的解释量均降低了0.3%.油松中午叶片水势显著高于沙棘且变异系数（7.3%）低于沙棘（11.7%）,而沙棘具有较高的叶片气孔导度,因此可以判断出油松属于恒水型植物,沙棘属于变水型植物.

英文摘要：

The dynamic changes of sap flow density （ Js ） of Pinus tabuliformis and Hippophae rhamnoides in plantations from July to September in 2015 was monitored through thermal dissipation probe in the hilly region of the Loess Plateau. In addition, plant physiological characteristics were analyzed to determine the water use types of these two species. The results indicated that the daily changes of Js of P. tabuliformis and H. rhamnoides showed a single peak during both pre- and postprecipitation. The Js of P. tabuliformis in growing season （ 12.62 mL · m-2· s-1 ） was significantly higher than that of H. rhamnoides （2.60 mL · m-2 · s-1）. The Js of these two species were significantly positively correlated with photosynthetic active radiation, vapor pressure deficit, soil volumetric water content （SWC）. The Js of these two species were mainly influenced by meteorological fac- tors during pre- and post-precipitation in both August and September. The contribution of SWC to Js of H. rhamnoides increased by 4.2% after precipitation in September, but the contribution of SWC to Js of P. tabuliformis decreased by 0.3% after precipitation in both August and September, respec- tively. Meanwhile, P. tabuliformis showed significantly higher water potential in midday leaf, but lower coefficient of variation （ 7 .3% ） than H. rhamnoides with the coefficient of variation of 11.7%.However, H. rhamnoides exhibited higher leaf stomatal conductance. Thus, P. tabuliformis and H. rhamnoides could be considered as isohydry and anisohydry species, respectively.