Abstract: The net photosynthetic rate,transpiration rate and water content of assimilating shoots of Haloscyion ammodendron and H. persicum were measured under different radiation intensities, temperatures changes and different water status. Their water potential under different water status was also measured. The experimental results showed. (1) The dependence of photosynthetic rate and transpiration rate on radiation intensit in the two species of Haloscylon. The increase of net photosynthetic rate and transpiration rate of H. arnrnodendron depending on radiation intensity was lower than that of H. persicurn. Two species of Haloxylon also maintained high transpiration rate under dark. (2) The average transpiration rate of H. persicurn was lower than H. arnrnodendron,showing that H. persicurn utilized water more efficiently than H. arnrnodendron. (3)The optimal temperature of photosynthesis of H. arnrnodendron was 24–32℃ and the optimal temperature of water utilization of H. arnrnodendron was 23. 5–25℃. (4) The water potential of H. amrnodendron was lower than –3.5 MPa whereas that of H. persicum was lower than –2.8MPa indicating that the two species of Haloscylon were under severe water stress ,and would lead to permanent wilting of their assimilating shoots.

Key words: Haloxylon ammodendron, H. persicum , Net photosynthetic rate , Transpiration rate , Transpiration coefficient