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BIOENERGETICS AND PHOTOSYNTHESIS

Environmental Effects on Oxygen Isotope Enrichment of Leaf Water in Cotton Leaves¹

Environmental Biology Group, Research School of Biological Sciences, Australian National University, Canberra, Australian Capital Territory 2600, Australia (F.R., N.M., H.S.-W., S.C.W., G.F.); Department of Crop Systems, Forestry, and Environmental Sciences, University of Basilicata, Potenza 85100, Italy (F.R., M.B.); and Laboratory of Forest Hydrology, Graduate School of Agriculture, Kyoto University, Kyoto 606–8501, Japan (N.M., M.T.)

The oxygen isotope enrichment of bulk leaf water (_b) was measured in cotton (Gossypium hirsutum) leaves to test the Craig-Gordon and Farquhar-Gan models under different environmental conditions. _b increased with increasing leaf-to-air vapor pressure difference (VPd) as an overall result of the responses to the ratio of ambient to intercellular vapor pressures (e_a/e_i) and to stomatal conductance (g_s). The oxygen isotope enrichment of lamina water relative to source water which increased with increasing VPd, was estimated by mass balance between less enriched water in primary veins and enriched water in the leaf. The Craig-Gordon model overestimated _b (and as expected. Such discrepancies increased with increase in transpiration rate (E), supporting the Farquhar-Gan model, which gave reasonable predictions of _b and with an L of 7.9 mm, much less than the total radial effective length L_r of 43 mm. The fitted values of L for of individual leaves showed little dependence on VPd and temperature, supporting the assumption that the Farquhar-Gan formulation is relevant and useful in describing leaf water isotopic enrichment.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Francesco Ripullone (francesco.ripullone{at}unibas.it).

www.plantphysiol.org/cgi/doi/10.1104/pp.107.105643

^* Corresponding author; e-mail francesco.ripullone{at}unibas.it.

Received July 19, 2007; accepted November 18, 2007; published December 7, 2007.