Multiple isotopic models using various kinetic fractionation coefficients to estimate δ18O of leaf water

Abstract

Investigation of{delta} 18O of leaf water may improve our understanding of the evapotranspiration partitioning and material exchange between the inside and outside of leaves. In this study,{delta} 18O of bulk leaf water ({delta}L,b) was estimated by both isotopic-steady-state (ISS) and non-steady-state (NSS) assumptions considering the Peclet effect. Specifically, we carefully modified kinetic fractionation coefficients (k). The results showed that the Peclet effect is required to predict{delta} L,b. On the diel time scale, both NSS assumption + Peclet effect (NSS + P) and ISS assumption + Peclet effect (ISS + P) using modified k (k-modified) for{delta} L,b showed a good agreement with observed{delta} L,b (p > 0.05). When using previously proposed k, however, both NSS + P and ISS + P were not reliable estimators of{delta} L,b (p < 0.05). On a longer time scale (days), estimates of daily mean{delta} L,b from ISS + P outperformed the estimates from NSS + P when using the same k values. Also, the employment of k-modified improved model performance in predicting daily mean{delta} L,b compared to the use of previously proposed k. Clearly, special care must be taken concerning k when using isotopic models to estimate{delta} L,b.\n\nHighlightFor hourly and daily mean data sets, the employment of modified kinetic fractionation coefficients significantly improved model performance for{delta} 18O of bulk leaf water.