黄土塬区苹果树干液流特征

应用热扩散式树干茎流计（TDP）于2012年7~10月对黄土塬区长武县苹果树干液流速率进行了连续测定，分析了气象因子、土壤含水率等多个环境要素对树干液流的影响。结果表明，在晴天和阴雨天苹果树干液流速率变化均呈明显的昼夜变化单峰曲线，晴天液流启动早，停止晚，液流速率大；阴雨天液流启动晚，停止早，液流速率小。苹果树干液流速率与太阳辐射、水气压差、大气温度和相对湿度呈显著正相关，与空气相对湿度呈显著负相关，晴天条件下液流速率与各气象因子的相关关系比阴雨天条件下显著，且均可用线性表达式来估算。在不同的土壤水分环境条件下，苹果树干液流速率变化差异很大。水分胁迫条件下，全天液流速率水平较低，反映其蒸腾水平低；而水分充足条件下，液流速率的变化过程为一宽峰曲线，维持较高液流速率的时间较长，全天蒸腾水平高。

Characteristics of Stem Sap Flow of Apple Trees in Loess Tableland

A thermal dissipation probe (TDP) was used to continuously measure the sap-flow rate of apple tree in Changwu county in loess tableland area of China from July to October, 2012. The effect of meteorological factors, soil moisture and other environment factors on sap flow was analyzed. The results showed that diurnal variation of the sap-flow rate of apple tree was a single peak curve in both sunny and rainy days. On sunny day, the sap-flow started more early and stopped more lately than on rainy day. The sap-flow rate of apple tree was positively correlated with solar radiation, vapor pressure deficit, atmospheric temperature and atmospheric relative humidity with a linear equation, and negatively correlated with air relative humidity. The dependency of sap-flow rate on various meteorological factors on the sunny day was more significant than on the rainy day. In addition, the sap-flow rate of apple tree varied distinctly in different environment conditions of soil moisture. Under the water stress condition, the sap-flow rate was significantly lower than that under the moist soil condition. The change of sap-flow rate showed a broad-peak curve, indicating that the transpiration was higher under the moist soil condition.