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