Abstract Reconstructing past responses of coastal wetlands to climate change contextualizes ongoing and future developments in these globally important ecosystems. The molecular distributions and stable isotope ratios (δ2H and δ13C) of sedimentary plant wax n-alkanes are frequently used to infer past vegetation and hydroclimate changes in wetland systems. However, there is limited modern information available about these compounds in subtropical wetlands. Here we analyzed mature leaves from 30 typical plant species and roots from 6 plant species collected in the Florida Everglades, including tree island plants, freshwater wetland plants, mangroves, and seagrass. The n-alkane abundance (2 to 884 µg/g dry weight), percent of aquatic plants ratio (Paq, 0 to 1), average chain length (ACL23-33, 24.0–30.7), concentration weighted average (CWA) δ2H (−231 to −78‰) and δ13C values (−38.9 to −14.4‰) spanned wide ranges with plant growth habit. Significant differences in n-alkane abundances, Paq, ACL23-33, CWA δ2H and δ13C values were found to exist between the leaves and roots of some emergent aquatic plants. Simple mass balance calculations of wetland aquatic plants suggest that long chain n-alkanes (e.g., C29 n-alkanes) are predominantly derived from leaves rather than roots in wetland surface sediments/soils. However, the contribution from mid-chain n-alkanes (e.g., C23 n-alkane) from roots may be equal to or greater than those from leaves. This implies that the differences in the isotopic compositions between root and leaf derived material need to be taken into account when interpreting down core changes in mid-chain n-alkane δ2H and δ13C values, which may be derived from variable contributions from leaves and roots rather than a change in hydroclimate or vegetation. Considering the large variation in both n-alkane distribution proxies and isotopic composition, no single molecular index or stable isotope ratio can capture multivariate changes of wetland ecosystems in the past. Nevertheless, principal component analysis shows promising potential to resolve different plant functional types. Paleo-reconstruction of subtropical aquatic ecosystems using n-alkanes will be most useful if the full molecular and isotopic distribution information of plant waxes are used.

中文翻译：

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典型植物沿陆-岸-海洋梯度分布的正构烷烃及其δ2H和δ13C值

摘要 重建沿海湿地对气候变化的过去响应，将这些全球重要生态系统的当前和未来发展置于背景之中。沉积植物蜡正构烷烃的分子分布和稳定同位素比（δ2H 和 δ13C）常用于推断湿地系统过去的植被和水文气候变化。然而，关于亚热带湿地中这些化合物的现代信息有限。在这里，我们分析了佛罗里达大沼泽地收集的 30 种典型植物物种的成熟叶和 6 种植物物种的根，包括树岛植物、淡水湿地植物、红树林和海草。正烷烃丰度（2 至 884 µg/g 干重）、水生植物比例百分比（Paq，0 至 1）、平均链长（ACL23-33，24.0-30.7），浓度加权平均值 (CWA) δ2H (-231 至 -78‰) 和 δ13C 值 (-38.9 至 -14.4‰) 跨越广泛的植物生长习性范围。发现一些挺水水生植物的叶和根之间存在正构烷烃丰度、Paq、ACL23-33、CWA δ2H 和 δ13C 值的显着差异。湿地水生植物的简单质量平衡计算表明，长链正构烷烃（例如，C29 正构烷烃）主要来自湿地表层沉积物/土壤中的叶子而不是根。然而，来自根的中链正构烷烃（例如，C23 正构烷烃）的贡献可能等于或大于来自叶子的贡献。这意味着在解释中链正构烷烃 δ2H 和 δ13C 值的向下核心变化时，需要考虑根和叶衍生材料之间同位素组成的差异，这可能来自叶和根的可变贡献，而不是水文气候或植被的变化。考虑到正构烷烃分布代理和同位素组成的巨大变化，过去没有单一的分子指数或稳定的同位素比可以捕捉湿地生态系统的多元变化。尽管如此，主成分分析显示出解决不同植物功能类型的潜力。如果使用植物蜡的完整分子和同位素分布信息，使用正烷烃对亚热带水生生态系统进行古重建将是最有用的。过去没有单一的分子指数或稳定的同位素比值能够捕捉湿地生态系统的多元变化。尽管如此，主成分分析显示出解决不同植物功能类型的潜力。如果使用植物蜡的完整分子和同位素分布信息，使用正烷烃对亚热带水生生态系统进行古重建将是最有用的。过去没有单一的分子指数或稳定的同位素比值能够捕捉湿地生态系统的多元变化。尽管如此，主成分分析显示出解决不同植物功能类型的潜力。如果使用植物蜡的完整分子和同位素分布信息，使用正烷烃对亚热带水生生态系统进行古重建将是最有用的。