Assessment of leaf water enrichment of Platycladus orientalis using numerical modeling with different isotopic models

Abstract Investigation of leaf water enrichment may improve our understanding of evapotranspiration partitioning and material exchange between the inside and the outside of leaves. In this study, with measurements of diel variations in δ18O of bulk leaf water (δL,b) of Platycladus orientalis, two theories (the Peclet effect and the two-pool model) describing leaf water enrichment were assessed. The proportional difference between observed and modeled leaf water enrichment, f, was estimated using both isotopic-steady-state (ISS) and non-steady-state (NSS) models to test the two theories. The results showed that differences between ISS- and NSS-modeled leaf water enrichment at the evaporative sites (Δl,e) were not significant (p > 0.05), thus estimated f was not significantly (p > 0.05) influenced by assuming ISS or NSS conditions. Under both ISS and NSS conditions, no significant (P > 0.05) positive f–Tr (leaf transpiration rate) relationships were found on either diel or diurnal time scales, indicating that the Peclet effect is not required to describe bulk leaf water enrichment. Therefore, it would be adequate to combine the simple two-pool model with the ISS model to predict δ18O of bulk leaf water of P. orientalis. These results may have implications for parameterizing the carbon cycle, past climates, and evapotranspiration partitioning models.