Seasonal variations of leaf wax n -alkane distributions and δ 2 H values in peat-forming vascular plants from the Dajiuhu peatland, central China

Leaf wax n -alkane compositions have been widely applied to reconstruct paleoclimate histories in peat deposits, yet understanding of how the n -alkanes vary during seasonal plant growth remains limited. Here we report variations in the molecular and wax-derived n -alkane hydrogen isotope ( δ 2 H alk ) in the three dominant vascular plant species ( Sanguisorba officinalis, Carex argyi, Euphorbia esula ) and surface peat deposits nearby from the Dajiuhu peatland over a growing season. All three species show a relatively high carbon preference index (CPI) in the beginning of the growing season, with the CPI values reaching as high as 50 in two of the three species. Two species ( S. officinalis, E. esula ) display relatively stable average chain length (ACL) values over the four sampling intervals, with standard derivations of 0.2–0.3. In contrast, C. argyi exhibits a significant fluctuation of ACL values (averaging 28.1 ± 1.4) over the growing season. The δ 2 H alk in all three species decreased during leaf growth. In the final stage of growth, the δ 2 H alk values of the three species are similar to those in the surface peats collected from the peatland. Combining the results of our measurements of alkane concentration and δ 2 H values, it is likely that de novo synthesis of leaf wax n -alkanes in the peat-forming plant species is mainly at the early stage of leaf development. In the following months, the removal process exceeds renewal, resulting in a general decrease of the concentration of the total n -alkanes and the integrated δ 2 H alk values. Thus the δ 2 H alk values probably integrate the environmental variations at the end of the plant growth period rather than the whole period or the early growth period. These results are significant and have the potential to improve the utility of δ 2 H alk values in paleoenvironmental reconstructions.