Abstract We investigated the seasonal variations of the molecular and hydrogen isotopic compositions of leaf cuticular n-alkanes (δDalk) in two subtropical deciduous tree species (Quercus chenii, Liquidambar formosana) over a three-year period. Average chain length values of long chain n-alkanes in both species are lower in young leaves than in mature ones. The δDalk values in both tree species show seasonal fluctuations that can be as large as 78‰ in a single year. The seasonal changes in molecular and isotopic compositions suggest that leaf wax n-alkanes in these subtropical deciduous tree species integrate environmental information over a large portion of the annual growth cycle in response to fluctuations in environmental stresses (e.g. storms, droughts). In addition, the changes reveal that seasonal patterns of δDalk can differ between different deciduous species at the same location and among different years. Spring leaves collected in 2014 had more negative δDalk values than those collected in 2015 and 2016, possibly responding to differences in annual precipitation D/H ratios and associated atmospheric circulation. These preliminary results highlight that extended seasonal monitoring of leaf wax δDalk values can improve their application to reconstructing paleohydrological histories.

中文翻译：

---

两种亚热带落叶树种叶蜡正构烷烃分子组成和δD值的季节性变化：华中地区三年监测结果

摘要 我们研究了三年内两种亚热带落叶树种（Quercus chenii、Liquidambar formosana）的叶表皮正构烷烃（δDalk）分子和氢同位素组成的季节性变化。两个物种中长链正构烷烃的平均链长值在幼叶中低于成熟叶。两种树种的 δDalk 值都表现出季节性波动，一年内可高达 78‰。分子和同位素组成的季节性变化表明，这些亚热带落叶树种中的叶蜡正烷烃整合了大部分年生长周期中的环境信息，以响应环境压力（例如风暴、干旱）的波动。此外，这些变化表明δDalk的季节性模式在同一地点和不同年份的不同落叶物种之间可能有所不同。2014 年收集到的春叶的 δDalk 负值比 2015 年和 2016 年收集的要多，这可能与年降水 D/H 比和相关大气环流的差异有关。这些初步结果突出表明，对叶蜡 δDalk 值的扩展季节性监测可以改进它们在重建古水文历史方面的应用。