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

Knowledge of hydrogen isotopic fractionation (c) of plant leaf waxes is the foundation for applying hydrogen isotope values (82H) in environmental reconstructions. In this work, we systematically investigated plant c values (calk/precipitation, calk/soil water, calk/leaf water and calk/lake water, representing the isotopic fractionation between plant n-alkane 82H and precip-itation 82H, soil water 82H, leaf water 82H and lake water 82H) from the natural environments and manipulation exper-iments. The results show that the calk/precipitation values of terrestrial plants have large variations (from -190 %o to -20 %o) and become more negative with increasing aridity index. This phenomenon is possibly caused by the 82H 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 82H values are generally higher than soil water 82H values, and the latter are higher than precip-itation 82H values. This finding further demonstrates that the evapotranspiration effect on source water 82H affects the quantification of the leaf wax apparent c values (calk/leaf water < calk/soil water < calk/precipitation). The calk/lake water values of submerged plants display a smaller range (-153 +/- 5 %o) than the calk/precipitation values of terrestrial plants, which is close to the terrestrial calk/precipitation values in humid areas. Therefore, the biosynthetic c value of terrestrial plant leaf waxes is relatively constant (ca. -153 +/- 5 parts per thousand), and the observed variable apparent Calk/precipitation 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 82H values of leaf waxes to trace environmental changes.

Automated summary

Knowledge of hydrogen isotopic fractionation of plant leaf waxes is crucial for using hydrogen isotope values in environmental reconstructions. This study systematically investigated the fractionation values between plant n-alkane 82H and various water sources, and found that the values are influenced by evapotranspiration and climatic conditions. The results emphasize the importance of considering evapotranspiration effects when using leaf wax 82H values to trace environmental changes.