| Basing on physiological ecology, we have studied some main tree species in Semi-arid Region on Loess Plateaus. The method of potted plant trial and plantation survey was adopted to study the characteristics of transpiration on different situations, and a comprehensive survey on the practical growth condition of studied tree species was conducted to evaluate the adaptation quality of tree species in Semi-arid Region. The transpiration rates, water consumption and the main influencing factors of Ulmus pumila, Robinia pseudoacacia, Platycladus orientalis,Pinus tabulaeformis in Semi-arid Region in Shanxi province was studied in this paper. The main results were below:1. Penman-Monteith equation was considered as a basic model to predict plantation transpiration. The model was built on meteorological data obtained by weather location and timing observation of plantation evaporation using Li-1600 steady stomameter, and automatic weather station on all parameters such as net radiation in forest canopy, light reduction coefficient, canopy resistance and net radiation. And put all data into predicted equation to accurately predict plantation transpiration in growing seasons. The results showed there existed a good correlation between observed value and predicted value, and the equation can exactly predict transpiration of the studied plantations.2. The transpiration process of the four species showed a single peak features. For water consumption, the four species were suitable to be a local tree species, the order of the average daily transpiration from high to low were Robinia pseudoacacia, Ulmus pumila, Pinus tabulaeformis, Platycladus orientalis. The results indicated that the daily transpiration of the Broad-leaved forest are higher than the Coniferous forest regardless of affection of the LAI and the soil water content.3. Using the sap flow method and Penman-Monteith modified equation to simulate the monthly transpiration of Robinia pseudoacacia and Platycladus orientalis. The results of two methods were closed:The simulated transpiration of Robinia pseudoacacia was 224.78mm, while the measured transpiration was 246.27mm, and transpiration simulated by Penman-Moteith model of Ulmus pumila was 231.32mm. To select a specific date to simulate the daily transpiration of Robinia pseudoacacia, Ulmus pumila, Pinus tabulaeformis, Platycladus orientalis and to measure the light reduction coefficient and LAI were the key to improve accuracy.4. In month of June to August, the potential evaporation of Robinia pseudoacacia was 617.22mm, soil evaporation was 113.31mm, potential evapotranspiration was 340.25mm. The total rain fall was 349.22mm, which could satisfy the demand of the forest growth because in the whole growth season, the total rain fall was greater than total evapotranspiration. The contribution coefficients in this three month were 1.44,1.59 and 1.95 respectively.5. The results of the changes of stem flow on different climate situations showed that the flow rate had great differences under different weather conditions. The transpiration process of Robinia pseudoacacia showed broad-peak curve in sunny day, but showed double-peak curve in the cloudy day, and the start time of the stem flow was delayed in rainy day. The sap flow of the Ulmus pumila, Platycladus orientalis,Pinus tabulaeformis showed similar changes in sunny and cloudy day, especially for Pinus tabulaeformis, it had little change in day and night. The sap flow was affected by all kinds of comprehensive meteorological factors, and different species had different respond to the same factors.
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