Chin J Plan Ecolo ›› 2008, Vol. 32 ›› Issue (4): 961-966.doi: 10.3773/j.issn.1005-264x.2008.04.026
• Research Articles •
WEN Xue-Fa; ZHANG Shi-Chun;SUN Xiao-Min; YU Gui-Rui
There is considerable interest in the use of atmospheric C18O16O and 18O16O as a tracer for resolving the role of the terrestrial biosphere in the global carbon cycle. Leaf transpiration will result in the enrichment of the heavy H218O isotopes. The δ18O of leaf water at the evaporating site in the stomatal cavity directly influences the C18O16O and 18O16O exchanges, instead of that of the bulk leaf water. How to best quantify this enrichment effect remains an active area of research. In the past, a closed form of the Craig-Gordon model was obtained by invoking the steady-state assumption (δ18O of the transpired water is identical to δ18O of the xylem water). For the purpose of verification, the predictions of Craig- Gordon model are compared with δ18O of the bulk leaf water after appropriate corrections for the Péclet effect. On small time scales of minutes to hours, δ18O of the transpired water is variable in field conditions, implying that the steady state assumption is invalid. Recently, in-situ δ18O and δD measurement technology has been developed that has potential for improving our understanding of isotopic exchanges between the Earth’s surface and the atmosphere. The precision of hourly δ 18O and δD is comparable to the precision of mass spectrometry. It has the potential to improve prediction of δ18O of leaf water at the evaporating site within the stomatal cavity for the temporal dynamics of atmospheric water vapor δ18O and the δ18O of the transpired water, especially if its measurement is made in a non-destructive manner and on a continuous basis. Because the isotopic flux of δ18O and δD is influenced by a similar set of biological and meteorological variables, simultaneous observations of δ18O and δD will provide additional constraints on the hydrological and ecological processes of the ecosystem. We review the theory and measurement techniques for the enrichment of H218O in leaves and focus on the recently developed in-situ measurement technology and its potential for improving our understanding of H218O enrichment in leaf water and C18O16O and 18O16O exchanges between the ecosystem and atmosphere.
WEN Xue-Fa, ZHANG Shi-Chun, SUN Xiao-Min, YU Gui-Rui. RECENT ADVANCES IN H218O ENRICHMENT IN LEAF WATER[J].Chin J Plan Ecolo, 2008, 32(4): 961-966.
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