| Populus euphratica Population is mainly distributed among arid and semi-arid area. As a dominant special in these areas, Populus euphratica Population is well known for its high stress tolerance. It has various leaf shapes and is honored as"living fossil".Populus euphratica Population in Ebinur Lake had been used as materials for the research. The quantity characters of Populus euphratica Population was surveyed in the field. This research made use of the open gas exchange system, Li-6400 Portable Photosynthesis System, was carried on the research on natural Populus euphratica 's photosynthetic rate(Pn),transpiration rate (E) and water use efficiency (WUE) . The research studied the changes of Populus euphratica's gas exchange parameters in the pressure of water and the changes of some kinds of important photosynthetic physiological factors and the physiological factors to deal with arid environment.The results showed that:(1) There are correlations between the quantity characters of Populus euphratica Population and physical and chemical indicators of the soil. The density of population,dbh and height of Populus euphratica are related closely with the water content,PH and other indexes of the soil.(2) The daily curse curve of Populus euphratica photosynthetic rate (Pn) and transpiration rate (E) can be divided into two types, which are single-peak curve and two peaks curve, and they have typical lunch break phenomenon. In different age, old tree was two peaks curve, young tree was single-peak curve.(3) The photosynthetic rate of Populus euphratica with different age and water use efficiency (WUE) seasonal changes both are August>October. There were great correlations between the photosynthetic rate of Populus euphratica and water use efficiency but few correlations between the transpiration rate and water use efficiency (WUE).(4) Photosynthetic capacity of Populus euphratica with different dbh had a great change with the water condition. The better of the water condition, the stronger of the photosynthetic capacity was. For the young, its water use efficiency (WUE) can be improved by water pressure. For the old and middle tree, its water use efficiency (WUE) can be reduced by water pressure. The parameters of photosynthesis rate light-response curve patterns of Populus euphratica have great differences between water-stress sample plot and non-water-stress sample plot. Light use efficiency can be reduced by water pressure.(5) In the sample without water-stress, related coefficient of main influence factors and Pn from big to small in proper order is RH,VpdL,Tleaf,Tair,Gs,RAR. Related coefficient of main influence factors and E from big to small in proper order is VpdL,Gs,RH,Tleaf,Tair,RAR; In the water-stress sample plot, Related coefficient of main influence factors and Pn from big to small in proper order is RH,VpdL,Tair,RAR,Tleaf,Gs. Related coefficient of main influence factors and E from big to small in proper order is RH,VpdL,Tair,Tleaf,RAR,Gs。(6) Seasonal changes in photosynthetic pigment of Populus euphratica Population were great. It was highest in the August, followed by June, and lowest in the October. Soluble sugar was highest in the August, followed by June, and lowest in the October. Soluble protein was highest in the October, followed by August, and lowest in the June. In the sample suffered with water pressure, soluble sugar content was lower then that in the average sample, but soluble sugar content was higher then that in the average sample.(7) In the sample suffered with water pressure, POD activity and SOD activity of Populus euphratica Population with different dbh were all higher than that in the average sample. In the sample suffered with water pressure, MDA content of Populus euphratica Population with different dbh was lower than that in the average sample. In the sample suffered with water pressure, proline content of Populus euphratica Population with different dbh was higher than that in the average sample.
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