Apparent fractionation of hydrogen isotope from precipitation to leaf wax n-alkanes from natural environments and manipulation experiments.

Knowledge of hydrogen isotopic fractionation (ε) of plant leaf waxes is the foundation for applying hydrogen isotope values (δH) in environmental reconstructions. In this work, we systematically investigated plant ε values (ε, ε, ε and ε, representing the isotopic fractionation between plant n-alkane δH and precipitation δH, soil water δH, leaf water δH and lake water δH) from the natural environments and manipulation experiments. The results show that the ε values of terrestrial plants have large variations (from -190 ‰ to -20 ‰) and become more negative with increasing aridity index. This phenomenon is possibly caused by the δH changes in source water (from precipitation to soil water and then to leaf water) during plant leaf wax synthesis under various evapotranspiration conditions in different climatic zones. The rainfall manipulation experiments show that leaf water δH values are generally higher than soil water δH values, and the latter are higher than precipitation δH values. This finding further demonstrates that the evapotranspiration effect on source water δH affects the quantification of the leaf wax apparent ε values (ε < ε < ε). The ε values of submerged plants display a smaller range (-153 ± 5 ‰) than the ε values of terrestrial plants, which is close to the terrestrial ε values in humid areas. Therefore, the biosynthetic ε value of terrestrial plant leaf waxes is relatively constant (ca. -153 ± 5 ‰), and the observed variable apparent ε values are possibly caused by the varied degree of evapotranspiration effect on the water that plants used in different climatic conditions. This effect should be considered when applying δH values of leaf waxes to trace environmental changes.