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The photosynthetic characters and water use efficiency of the desert plants Haloxylon ammodendron and Calligonum mongolicum, which grow in conditions of extreme stress, were studied. The mechanisms of their acclimation to harsh desert conditions and their potential capacity for sand stabilizing are revealed. The stable carbon isotope ratios (delta(13)C or C-13/C-12) of leaves or assimilating shoots of desert plants growing at the southern edge of the Badain Jaran Desert were analyzed by mass spectrometry and compared. The diurnal course of net photosynthesis rate (Pn), Pn/light and Pn/CO2 curves, and water use efficiency (WUE, Pn/E) were measured by using the LI-6400 Portable Photosynthesis System. The results showed that: (1) Assimilating shoots of H. ammodendron and C. mongolicum have Kranz anatomy; (2) The delta(13)C values of H. ammodendron and C. mongolicum were -14.3% and -14.8%, respectively, whereas the corresponding values of Caragana korshinskii, Nitraria sphaerocarpa, Hedysarum scoparium, and Reaumuria soongorica were -25.8%, -25.8%, -26.4%, and -28.1%, respectively; (3) The CO2 compensation points (CCP) of H. ammodendron and C. mongolicum were 1.6 and 4.3 mumol mol(-1), respectively, and those of C korshinskii and H. scoparium were 90.7 and 86.3 mumol mol(-1), respectively; (4) The light saturation points (LSP) of H. ammodendron and C mongolicum were 1660.0 and 1755.6 mumol m(-2) s(-1), respectively, and those of C korshinskii and H. scoparium were 1266.7 and 1394.4 mumol m(-2) s(-1), respectively. It was concluded that H. ammodendron and C. mongolicum belong to C, plants, while C. korshinskii, N. sphaerocaroa, H. scoparium, and R. soongorica are C, plants. The annual WUE of the five desert plants was ranked in the following order: H. ammodendron > C. mongolicum > C. korshinskii > H. scoparium approximate to N. sphaerocarpa > R. soongorica. For estimation of the long-term WUE of desert plants by delta(13)C values of leaves or assimilating shoots, the best period of time for sampling in temperate desert regions is between late August and late September.