The Studies On The Relationship Of Trees Water Physiology Characteristics And Soil Water In Semi-arid Region On Loess Plateaus

The studies on the relationship of forest water physiology characteristics of tree and soil water relation on the Loess PlateauWater shortage has been a problem of social concern in semi-arid region on the Loess Plateau. It is also an important factor which limits the development of local forestry. Ulmus pumila, Pinus tabulaeformis, Caragana microphylla, Robinia pseudoacacia, Platycladus orientalis and Hippophae rhamnoides were selected for the study objects based on the theory of soil-plant-atmosphere continuum. The experiment site was located at Experiment Station of Beijing Forestry University, Fangshan County, Shanxi Province. The photosynthesis of trees, transpiration, water consumption and other physiological characteristics were detected by Li-6400photosynthesis measurement system and Li-1600steady promoter and other equipments. The differences of drought tolerance and appropriate soil moisture of different forest species were analysed in detail. The results could provide the scientific base for selection of drought tolerant trees, assessment of preferred soil water of forest land and accurate estimation of ecological water consumption of forest vegetation.The main content of this study is:(1) Dynamic analysis of precipitation resource in semi-arid region on Loess Plateaus;(2) The study of forest of water Use and photosynthesis relationship;(3) The study of Suitable soil moisture in tree growth;(4) The research of Trees Transpiration Characteristics;(5) The research of Stand evapotranspiration;The conclusions are:The average annual precipitation of more than50years in study area is just416mm, and has the trend of decline in recent years; major drought in the study area factor is cause by precipitation mainly concentrated in the summer, precipitation of late spring and early summer is lower, and shortage of autumn and winter fill soil moisture. In the analysis process of the mechanism of the physiological effects of forest trees, the main purpose of six tree species suitable for soil moisture conditions were sure by the pot experiment and soil moisture analysis, which was improving photosynthetic rate and water use efficiency. The suitable soil water range of Ulmus pumila, Pinus tabulaeformis, Caragana microphylla, Robinia pseudoacacia, Platycladus orientalis and Hippophae rhamnoides are respectively10.8%-13.7%,11.2%%-12.7%,10.1%-14.7%,9.9%-13.2%, and11.6%-13.1%. In the study of the evapotranspiration simulation, different densities during the2008growth period were calculated by Penman-Monteith formula. The results are average transpiration of Ulmus pumila, Caragana microphylla is209.5mm,239.3mm and178.4mm; in2007, it is182.6mm,199.5mm and141.0mm. The error range of measured and simulated values is within of14%. It means that the Penman-Monteith equation can be more accurately simulate the local forest transpiration. Actual evapotranspiration of flux method pine, Ulmus pumila and Caragana microphylla were analyzed and calculated by P-M synthesis method and location. The value from P-M positioning integrated flux is higher than the value from location.The relative error of two methods is about12%, it means they both can accurately reflect the actual forest evapotranspiration. There are close relationship between physiological characteristics and soil moisture, and the forest trees can grow healthily only in the appropriate range of soil moisture.