中文摘要：

水分供应不足及水热不同步常导致黄土丘陵地区在春末和夏初出现季节性干旱。为阐明该地区主要造林树种的蒸腾耗水特征及其对降水的响应,使用热扩散式树干茎流计（TDP）于2009年4–10月对黄土丘陵区安塞国家生态试验站刺槐（Robinia pseudoacacia）和侧柏（Platycladus orientalis）的树干液流密度（Fd）进行连续观测,并同步测定了气象、土壤水分等环境因子。结果表明：刺槐和侧柏在生长季内不同生长时期的Fd均表现为单峰型日变化特征,刺槐最高液流峰值为0.120 68m3·m^–2·h^–1,是侧柏最高液流值（0.037 37 m^3·m^–2·h^–1）的3.23倍。除生长旺盛季（7–8月）外,刺槐和侧柏降水后的Fd明显高于降水前。同时反映水汽压差（VPD）和太阳辐射（Rs）的蒸腾变量（VT）能够很好地模拟Fd,且两者呈显著的指数正相关关系,随VT的增加Fd逐渐增大,VT增加到50 k Pa（W·m^–2）1/2左右时,Fd的变化趋于稳定;通过对降水前后两个树种水力导度（拟合参数b值）分析,相对于侧柏,刺槐更易受降水的影响（p〈0.001）。因此,可认为刺槐是降水敏感型植物,而侧柏是降水不敏感型植物。该研究通过分析黄土丘陵区人工林树种对降水的差异性响应,从树木水分利用方面能够为当地生态恢复过程中人工林的管理提供科学依据。

英文摘要：

Aim In the loess hilly region, drought stress frequently occurs during the late spring and early summer as a result of insufficient water supply and asynchronous changes between temperature and precipitation. Our objective was to quantify the characteristics of water-consumption through transpirations and their responses to precipitation in the dominant plantations in this region. Methods Thermal dissipation probe（TDP） was used to measure the sap flow density（Fd） of Robinia pseudoacacia and Platycladus orientalis from April through October in 2009 in Ansai National Ecological Experimental Station. Environmental variables, including meteorological factors and soil water content, were simultaneously measured. Important findings The diurnal variation of Fd exhibited a single-peak curve during the growing season of R. pseudoacacia and P. orientalis. The maximum Fd was three times greater in R. pseudoacacia（0.120 68 m^3·m^-2·h^-1 than that in P. orientalis（0.037 37 m^3·m^–2·h^–1. Except in the rapid-growth season（July to August）, the Fd of these two species during the post-precipitation period were significantly higher than that during the pre-precipitation period. The Fd of P. orientalis and R. pseudoacacia was well fitted with transpiration（VT）, an integrated index calculated from both vapor pressure deficit（VPD） and solar radiation（Rs）, using an exponential saturation function. Generally, Fd increased in response to rising VT, while these values tended to be stable whenVT reached about 50 k Pa（W·m^–2）1/2. Furthermore, R. pseudoacacia showed more sensitive to precipitation（p 0.001） than P. orientalis, according to different hydraulic conductance model coefficients（fitting parameter b） between pre- and post-precipitation periods. Therefore, R. pseudoacacia could be considered as a precipitation-sensitive species, while P. orientalisasa precipitation-insensitive species. Through analyzing the different responses of plantation species to precipitation in the loess hill