Different hydrogen isotope fractionations during lipid formation in higher plants: Implications for paleohydrology reconstruction at a global scale

Leaf wax δD(n-alkane) values have shown to differ significantly among plant life forms (e.g., among grasses, shrubs, and trees) in higher plants. However, the underlying causes for the differences in leaf wax δD(n-alkane) values among different plant life forms remain poorly understood. In this study, we observed that leaf wax δD(n-alkane) values between major high plant lineages (eudicots versus monocots) differed significantly under the same environmental conditions. Such a difference primarily inherited from different hydrogen biosynthetic fractionations (ε(wax-lw)). Based upon a reanalysis of the available leaf wax δD(n-alkane) dataset from modern plants in the Northern Hemisphere, we discovered that the apparent hydrogen fractionation factor (ε(wax-p)) between leaf wax δD(n-alkane) values of major angiosperm lineages and precipitation δD values exhibited distinguishable distribution patterns at a global scale, with an average of −140‰ for monocotyledonous species, −107‰ for dicotyledonous species. Additionally, variations of leaf wax δD(n-alkane) values and the ε(wax-p) values in gymnosperms are similar to those of dicotyledonous species. Therefore, the data let us believe that biological factors inherited from plant taxonomies have a significant effect on controlling leaf wax δD(n-alkane) values in higher plants.