Evaluating the response of δ 13 C in Haloxylon ammodendron , a dominant C 4 species in Asian desert ecosystems, to water and nitrogen addition as well as the availability of its δ 13 C as an indicator of water use efficiency

[摘要] 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 ( δ 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 δ 13 C of H. ammodendron . Furthermore, H. ammodendron is a C 4 plant; whether its δ 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 δ 13 C and gas exchange of H. ammodendron . Then we calculated the degree of bundle-sheath leakiness ( φ ) and WUE of the assimilating branches of H. ammodendron . δ 13 C and φ 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, δ 13 C had no correlation with WUE. These results were associated with the irrelevance between δ 13 C and the ratio of intercellular to ambient CO 2 concentration ( c i   /   c a ), which might be caused by a special value (0.37) of the degree of bundle-sheath leakiness ( φ ) or a lower activity of carbonic anhydrase (CA) of H. ammodendron . In conclusion, δ 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.

[学科分类] 大气科学