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

Several recent studies showed that leaf wax n-alkane delta H-2 values (delta H-2(wax)) within a leaf were heterogeneous in a small number of species. It still remains unclear whether the heterogeneity of intra-leaf delta H-2(wax) values is general for various species, how delta H-2(wax) values vary spatially and temporally, and whether there is a common explanation for the intra-leaf delta H-2(wax) heterogeneity in higher plants. Here we compared the hydrogen isotope compositions of leaf wax and corresponding leaf water (delta H-2(lw)) across leaf sections among a variety of monocot and dicot plant species. There is significant and consistent heterogeneity for both delta H-2(wax) and delta H-2(lw), 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 delta H-2(wax) and delta H-2(lw) for dicots. The consistent occurrence of variations of delta H-2(lw) and delta H-2(wax) values within a leaf imply that delta H-2(wax) values probably inherit point-to-pint from in-situ delta H-2(lw) values, and thus the intra-leaf delta H-2(wax) heterogeneity mainly results from the spatial pattern of intra-leaf delta H-2(lw) values associated with veinal structures between dicots and monocots. The general heterogeneity of intra-leaf delta H-2(wax) values further intensifies that it is necessarily needed for in-depth understanding leaf wax biomarker. (C) 2021 Elsevier B.V. All rights reserved