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The plants' sap flow can characterize water transpiration and consumption, reflect water transmission situation and then determine the vegetation ecological water requirement. This paper takes Haloxylon ammodendron and Tamarix as the research object, adopts thermal diffusion method([1]), studies vegetation trunk fluid flow characteristics and the relationship between the meteorological factors. The results show that: (1) Haloxylon ammodendron and Tamarix's sap flux density are showed obvious diurnal variation rule, there is a "nap" phenomenon. Haloxylon ammodendron's liquid sap flux density of monthly mean performance is July > June >August, and Tamarix is July > August >June. (2) Haloxylon ammodendron's flow start time in cloudy is delayed about 1 similar to 1.5 h or so than in sunny day, and Tamarix is about 0.5 h delay. (3) Haloxylon ammodendron and Tamarix's fluid sap flux density in each month are significantly related to meteorological factors, through the regression analysis, Haloxylon ammodendron and Tamarix's trunk liquid sap flux density can make a regression model with meteorological factors.

Water is not only the basic resources for survival plants, but also the decisive factor for arid ecological stable. Ecological water requirement, as an important part of water resources utilization, has an important significance of regional ecological security. Desert vegetation transpiration water is a key factor of ecological water requirement, water consumption of plant root absorption is more than 99.8% in transpiration([2]), so accurately estimating trunk rising fluid flow and determining transpiration water consumption become an important process for the calculation of ecological water requirement. The domestic and foreign scholars do lots of researches and practice on the plant transpiration water consumption measurement methods and means, mainly including: micrometeorological method, the water balance method, the method of plant physiology. Vorticity related method([3]) and bowen ratio method([4]) of micrometeorology method are the most widely used, their advantages are directly calculated water heat flux, get community average vertical water vapor flux. Weighing lysimeter([5]) is the most applied method of the water balance method, its advantages are the original soil of weighing, and can accurately measure the soil evapotranspiration water consumption, it is suitable for long-term positioning monitoring. Plant physiology method includes for the blade of isolated weighing method([6]), the stomatal meter([7]), photosynthesis instrument([8]), etc. In addition, in view of the individual plant stem flow meter measurement method (heat pulse, trunk heat balance, stem heat balance and thermal diffusion method) is by the idea of using heat pulse measurement to measure trunk SAP flow of Huber (1932), and constantly improve, and the ecologists Marshall used the technology for determination of trunk SAP flow([9]); Trunk thermal equilibrium method, invented by Cermak, is directly through the electronic heater and the inner temperature induction device to calculate trunk SAP flow, and without correction([10]); Thermal diffusion method, through temperature difference between the insert trunk sapwood probe and the experience formula between liquid flow density to calculate trunk SAP flow, is put forward by Granier([11]). This research adopts thermal diffusion method to reveal tree trunk SAP flow character of Haloxylon ammodendron and Tamarix, and analyses the relationship between fluid flow and temperature and air relative humidity and so on of the environmental factors. The paper reveals the relationship between Haloxylon ammodendron and Tamarix tree trunk fluid flow characteristics and environmental factors on its potential impact.