Abstract Reconstructions of climate using leaf wax D/H ratios (δDwax) require accounting for the apparent isotopic fractionation (eapp) between plant source water and waxes. There have been conflicting publications on whether plants in the Arctic growing under 24-hour continuous light, fractionate less than temperate and tropical plants. In this study, we examine the effect of diurnal light (DL) versus 24-hour continuous light (CL) on the isotopic composition of leaf n-alkanes and n-acids in greenhouse experiments using two common Arctic plants (Eriophorum vaginatum, or tussock cottongrass and Betula nana, or dwarf birch). For E. vaginatum, the δDwax values of various wax homologues were 5–11‰ more positive for CL plants relative to their DL counterparts, whereas for B. nana, CL waxes were 3–24‰ more negative, suggesting that daylight length is not a unifying control on leaf wax D/H ratios of Arctic plants. The δ13Cwax of B. nana was more negative for plants grown in continuous light compared to diurnal light, reflecting lower water-use efficiency, associated with prolonged stomatal opening in the CL treatment. We modeled the impact of increasing stomatal conductance and effective flow path lengths (mimicking variable leaf morphologies) on the isotopic composition of leaf waters (δDlw) and find that variations in leaf-water enrichment may explain the variable δDwax responses seen between E. vaginatum and B. nana. We suggest that between-species differences in the δDlw response to light, and differences in the utilization of stored carbohydrates, were important for governing δDwax. Our greenhouse results suggest that Arctic plant leaf waxes do not consistently display reduced eapp values as a result of 24-hour day light, providing additional support for field observations.

中文翻译：

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连续光照对白桦和阴道毛蕊花叶蜡同位素比的影响：对北极古气候重建的影响

摘要 使用叶蜡 D/H 比 (δDwax) 重建气候需要考虑植物源水和蜡之间的表观同位素分馏 (eapp)。关于在 24 小时连续光照下生长的北极植物是否比温带和热带植物分馏少，存在相互矛盾的出版物。在这项研究中，我们在温室实验中使用两种常见的北极植物（Eriophorum vaginatum 或 tussock）检查了昼夜光照 (DL) 与 24 小时连续光照 (CL) 对叶正烷烃和正酸同位素组成的影响棉草和 Betula nana，或矮桦树）。对于 E. vaginatum，CL 植物的各种蜡同系物的 δDwax 值比它们的 DL 对应物高 5–11‰，而对于 B. nana，CL 蜡的负值高 3–24‰，表明日光长度不是北极植物叶蜡 D/H 比率的统一控制。与昼夜光照相比，在连续光照下生长的植物的 δ13Cwax 对 B. nana 的负面影响更大，这反映了较低的水分利用效率，这与 CL 处理中气孔开放时间延长有关。我们模拟了增加气孔导度和有效流动路径长度（模拟可变叶形态）对叶水同位素组成（δDlw）的影响，并发现叶水富集的变化可以解释在 E. vaginatum 和B.娜娜。我们认为 δDlw 对光响应的物种间差异以及储存碳水化合物利用的差异对于控制 δDwax 很重要。