| Aiming to solve the contradiction between demand for the extension of forest vegetation and the limited water supply in arid and semi-arid area and based on the theory of soil-plant-atmosphere continuum, the dissertation chose the main afforestation tree species of soil and water conservation in the station of "Runoff Forestry" of Beijing Forestry University in Fangshan Country, Shanxi Province in Growing Seasons from 2002 to 2004, utilized advanced apparatus, equipments and various approaches, systematically analyzed of relationship between wood production with water consumption and studied the ecophysiological characteristics of tree transpiration and water consumption. These studies could provides the scientific bases for accurately estimating ecological water consumption and the choice of tree species and the properly arrangement of stand density. The dissertation involved following aspects: Relationship between precipitation resource in semi-arid region and forest construction. The study on ecophysiological characteristics of eight main afforestation tree species. The suitable soil moisture condition of tree growth in semi-arid region on Loess Plateau. The soil moisture circumstance of woodland and woodland soil's water availability and productivity. The rule of testing woodland soil evaporation. The simulation and prediction of stand transpiration and water consumption. Total and component proportion of woodland evapotranspiration.The theoretical basis of the experimental design and conclusion analysis are the theory of water balance, soil physics, soil-plant-atmosphere continuum, foresthydrology and silviculture. The theoretical providence of factual data estimation arethe theory of soil hydrodynamics and aerodynamic principle and energy balanceequation.Major conclusions are summarized as follows:? Under the condition of free soil water stress, the diurnal changes of transpiration rate and stomatal conductance of eight main afforestation tree species display a signal-peak curve and that of water use efficiency peak in the early morning. The transpiration rate of coniferous trees was the lowest, whilst the broad leaved trees were the highest, and the shrub species fell between coniferous species and broad leaved species. When sorted by potential transpiration rate and stomatal conductance, the decreasing orders were: Robinia pseudoacacie,Ulmus pumilas Amorpha fruticosa, Hippophae rhamnoides, Primus armeniaca , Caragana korshinskii, Pinus tabulaeformis and Platycladus orientalis. The decreasing orders of water use efficiency were: Platycladus orientalis, Caragana korshinski, Pinus tabulaeformis , Robinia pseudoacacie , Amorpha fruticosa % Ulmus pumila , Hippophae rhamnoides , Prunus armeniaca. With the increase of soil water content the transpiration rate, stomatal conductance and water use efficiency increase under the different soil water content. Under the different soil water content the curve of photosynthesis with irradiance is different and presents a quadratic relation model. Under the high soil water content the sensitivity of photosynthesis with irradiance is low and has little or no relation with water and with the increase of water stress the sensitivity of photosynthesis with irradiance increases.? To increase water use efficiency, the suitable soil water condition and rules of woodland soil moisture of Robinia pseudoacacia and Platycladus oriental in semi-arid region on Loess Plateau are determined. The range of SWC being suitable to tree's growth of Robinia pseudoacacia and Platycladus oriental are respectively 11.0%-15.5% (52.0%-74.0% of saturated soil water content) and 9.5%-13.5% (45.0%-64.0% of saturated soil water content). The best SWC values are respectively 13.0% (62.0% of saturated soil water content) and 10.5% (50% of saturated soil water content) to tree's growth of Robinia pseudoacacia and Platycladus oriental. The allowable lowest SWC are respectively 10.0% (48.0% of saturated soil water content) and 8.5% (45.0% of saturated soi...
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