Variations in precipitation and atmospheric N deposition affect water and N availability in desert and thus may have significant effects on desert ecosystems. Haloxylon ammodendron is a dominant plant in Asian desert, and addressing its physiological acclimatization to the changes in precipitation and N deposition can provide insight into how desert plants adapt to extreme environments by physiological adjustment. Carbon isotope ratio ([delta].sup.13 C) in plants has been suggested as a sensitive long-term indicator of physiological acclimatization. Therefore, this study evaluated the effect of precipitation change and increasing atmospheric N deposition on [delta].sup.13 C of H. ammodendron. Furthermore, H. ammodendron is a C.sub.4 plant; whether its [delta].sup.13 C can indicate water use efficiency (WUE) has not been addressed. In the present study, we designed a field experiment with a completely randomized factorial combination of N and water and measured [delta].sup.13 C and gas exchange of H. ammodendron. Then we calculated the degree of bundle-sheath leakiness (Ï) and WUE of the assimilating branches of H. ammodendron. [delta].sup.13 C and Ï remained stable under N and water supply, while N addition, water addition and their interaction affected gas exchange and WUE in H. ammodendron. In addition, [delta].sup.13 C had no correlation with WUE. These results were associated with the irrelevance between [delta].sup.13 C and the ratio of intercellular to ambient CO.sub.2 concentration (c.sub.i / c.sub.a ), which might be caused by a special value (0.37) of the degree of bundle-sheath leakiness (Ï) or a lower activity of carbonic anhydrase (CA) of H. ammodendron. In conclusion, [delta].sup.13 C of H. ammodendron is not sensitive to global change in precipitation and atmospheric N deposition and cannot be used for indicating its WUE.