Effects of environmental parameters, leaf physiological properties and leaf water relations on leaf water δ 18 O enrichment in different Eucalyptus species

Stable oxygen isotope ratios ( δ 18 O) have become a valuable tool in the plant and ecosystem sciences. The interpretation of δ 18 O values in plant material is, however, still complicated owing to the complex interactions among factors that influence leaf water enrichment. This study investigated the interplay among environmental parameters, leaf physiological properties and leaf water relations as drivers of the isotopic enrichment of leaf water across 17 Eucalyptus species growing in a common garden. We observed large differences in maximum daily leaf water δ 18 O across the 17 species. By fitting different leaf water models to these empirical data, we determined that differences in leaf water δ 18 O across species are largely explained by variation in the Péclet effect across species. Our analyses also revealed that species‐specific differences in transpiration do not explain the observed differences in δ 18 O while the unconstrained fitting parameter ‘effective path length’ ( L ) was highly correlated with δ 18 O. None of the leaf morphological or leaf water related parameters we quantified in this study correlated with the L values we determined even though L was typically interpreted as a leaf morphological/anatomical property. A sensitivity analysis supported the importance of L for explaining the variability in leaf water δ 18 O across different species. Our investigation highlighted the importance of future studies to quantify the leaf properties that influence L. Obtaining such information will significantly improve our understanding of what ultimately determines the δ 18 O values of leaf water across different plant species.