On the ¹⁶O/¹⁸O isotope effect associated with photosynthetic O₂ production

While 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.