Tcherkez, GuillaumeFarquhar, Graham2015-12-101445-4408http://hdl.handle.net/1885/57848While photosynthetically evolved O2 has been repeatedly shown to have nearly the same oxygen isotope composition as source water so that there is no corresponding 16O/18O isotope effect, some recent 18O-enrichment studies suggest that a large isotope effect may occur, thus feeding a debate in the literature. Here, the classical theory of isotope effects was applied to show that a very small isotope effect is indeed expected during O2 production. Explanations of the conflicting results are briefly discussed.Keywords: Oxygen; Photosynthesis; Enrichment; Isotope composition; Isotope effects; Isotopes; isotopic composition; oxygen; oxygen isotope; photosynthesis; primary production200710.1071/FP071682015-12-09