Intra-leaf heterogeneities of hydrogen isotope compositions in leaf water and leaf wax of monocots and dicots

Abstract

Several recent studies showed that leaf wax n-alkane δ2H values (δ2Hwax) within a leaf were heterogeneous in a small number of species. It still remains unclear whether the heterogeneity of intra-leaf δ2Hwax values is general for various species, how δ2Hwax values vary spatially and temporally, and whether there is a common explanation for the intra-leaf δ2Hwax heterogeneity in higher plants. Here we compared the hydrogen isotope compositions of leaf wax and corresponding leaf water (δ2Hlw) across leaf sections among a variety of monocot and dicot plant species. There is significant and consistent heterogeneity for both δ2Hwax and δ2Hlw, i.e., base-to-tip 2H-enrichment for monocots (except Hemerocallis citrina, and Dactylis glomerata) whereas base-to-tip and center-to-edge increases in δ2Hwax and δ2Hlw for dicots. The consistent occurrence of variations of δ2Hlw and δ2Hwax values within a leaf imply that δ2Hwax values probably inherit point-to-pint from in-situ δ2Hlw values, and thus the intra-leaf δ2Hwax heterogeneity mainly results from the spatial pattern of intra-leaf δ2Hlw values associated with veinal structures between dicots and monocots. The general heterogeneity of intra-leaf δ2Hwax values further intensifies that it is necessarily needed for in-depth understanding leaf wax biomarker.