Expressing leaf water and cellulose oxygen isotope ratios as enrichment above source water reveals evidence of a Peclet effect

There is an increasing ecological interest in understanding the gradients in (H2O)-O-18 enrichment in leaf water (i.e. a Peclet effect), because an appreciation of the significance of the Peclet effect is important for improving our understanding of the mechanistic processes affecting the O-18 composition of leaf water and plant organic material. In data sets where both source water and leaf water O-18 data are available, we can evaluate the potential contribution of a Peclet effect. As an example, we recalculate data published earlier by Roden and Ehleringer (1999, Oecologia 121:467-477) as enrichments in leaf water (Delta(L)) and cellulose (Delta(cell)) above source water. Based on these recalculations, we present support for the relevance of a Peclet effect in leaves. Further, we demonstrate that the subtle variations in Delta(L) and Delta(cell) caused by a Peclet effect may be masked in experimental systems in which variation in the source water oxygen isotope ratio is considerable.