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On the isotopic composition of leaf water in the non-steady state

Farquhar, G. D. and Cernusak, Lucas A. (2005). On the isotopic composition of leaf water in the non-steady state. Functional Plant Biology,32(4):293-303.

Document type: Journal Article
Citation counts: Scopus Citation Count Cited 115 times in Scopus Article | Citations

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Title On the isotopic composition of leaf water in the non-steady state
Author Farquhar, G. D.
Cernusak, Lucas A.
Journal Name Functional Plant Biology
Publication Date 2005
Volume Number 32
Issue Number 4
ISSN 1445-4408   (check CDU catalogue open catalogue search in new window)
Scopus ID 2-s2.0-19544375950
Start Page 293
End Page 303
Total Pages 11
Place of Publication Collingwood
Publisher Commonwealth Scientific and Industrial Research Organization
Field of Research 0607 - Plant Biology
HERDC Category C1 - Journal Article (DEST)
Abstract An expression is derived for the isotopic composition of water in leaves under conditions where the composition of water entering the leaf is not necessarily the same as that of water being transpired. The treatment is simplified and considers the average composition of the lamina and of the sites of evaporation. The concept of 'isostorage' is introduced as the product of leaf water content and the isotopic enrichment of leaf water above source water. It is shown that the rate of increase of isostorage is minus the 'isoflux' through the stomata, with the latter expressed as the product of the transpiration flux and the enrichment of the transpired water beyond source water. The approach of the isostorage to the steady state depends on the deviation of the isotopic enrichment of water at the evaporating sites from the steady value, and on the gross (one way) diffusive flux out of the leaf. To achieve model closure, it is assumed that the relationship between leaf water enrichment and that at the sites of evaporation depends on the radial Péclet number in the same manner as in the steady state. The equations have an analytical solution, and we also show how to calculate the results simply using a commonly available computer tool. The form of the equations emphasises that the one-way fluxes of water into and out of the stomata must sometimes be considered separately, rather than as a net outward flux. In this narrow sense we come to the interesting conclusion that more water usually enters the leaf from the air than from the roots.
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Created: Wed, 11 Mar 2009, 14:46:10 CST by Sarena Wegener