Abstract: Monitoring and calculating the evapotranspiration and the relationship between supply and demand of water for Chinese Ephedra,an important medicinal plant in Mu Us Sandy Land,were conductive to better understanding of characters of water consumption and water physio-ecology. Evapotranspiration (ET) of Chinese Ephedra and its canopy micrometeorological factors in Mu Us Sandy Land was calculated and measured by eddy covariance technique and meteorology automatic monitoring system respectively in the growing season of 2004. ET and the relationship between supply and demand of water for Chinese Ephedra were analyzed. Main results were showed as follows:(1) in growing season,ET exhibited a large temporal variation. Its diurnal variation showed a single peak change in clear/cloudy days,a multi-peak change in overcast days. Regarding the daily variation,it increased in the beginning of the growing season,getting to peak in June and July,and decreased gradually in August,reaching the bottom in September. The average value and total amount of ET was 0.60mm/d and 93.6mm respectively. (2) There was a well multiple correlation (P<0.01,R2=0.731) between ET and the micrometeorology factors:global radiation (Ra),air temperature (Ta),relative humidity (RH) and wind speed (V). Ra was the most important micrometeorology factor that effected ET by the partial correlation coefficient. (3) The ratio of (R/TR) was 2.9. In terms of annual value,there was no water supply and demand conflict,or water shortage and water stress in the experiment area. However,in the beginning of the growing season,precipitation was not sufficient for water consumption,imposing constraint to the growing of Chinese Ephedra in its earlier growing season.

Key words: Mu Us Sandy Land, Mu Us Sandy Land, Chinese Ephedra, Evapotranspiration, Ratio of rainfall and transpiration