Stable carbon isotope composition (δ13C) of land snail materials is widely used as a proxy for reconstructing past vegetation and environmental changes. Interpretation δ13C data is challenging due to the complexities of snail physiology. This study cultured Lissachatina fulica (Bowdich, 1822) snails to investigate δ13C of their soft tissues and excrement under various plant types and dietary carbonate content. Our results show that snails primarily assimilate organic matter (OM), with limited use of dietary carbonates. δ13C of organic matter in excrement correlates positively with that in the diet, but exhibits deviations due to variable carbon isotopic fractionation during assimilation. Tissue δ13C (δ13Ctissue) is positively related to the δ13C of OM (δ13COM) in the diet, varying by turnover rates, with faster turnover rate, such as the digestive gland, exhibiting more negative δ13Ctissue values. Moreover, carbon isotopic fractionation between tissues and diet (Δ13Ctissue-OM) differs based on plant type. Snails fed with C3 plants show positive Δ13Ctissue-OM values, whereas those fed with C4 plants exhibit negative values. These Δ13Ctissue-OM values are far from equilibrium (Δ13Ctissue-OM = 0) with conditions of rapid snail growth. Our findings indicate that the snails fed with C3 and C4 plants result in distinct carbon isotopic fractionation, leading to the deviation in δ13C between plants and land snail materials (e.g., excrement, tissues, shells and shell-bound organic matter). A comprehensive model of carbon metabolism and isotopic fractionation in snails is proposed including the assimilation process from diet to soft tissues and excretion. This study highlights the importance of physiological factors such as growth rates and turnover rates when interpreting δ13C of land snail materials for paleoenvironmental reconstructions.

中文翻译：

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陆地蜗牛内的碳易位会影响碳同位素分馏


陆地蜗牛材料的稳定碳同位素组成 （δ13C） 被广泛用作重建过去植被和环境变化的代表。由于蜗牛生理学的复杂性，解释 δ13C 数据具有挑战性。本研究培养了 Lissachatina fulica （Bowdich， 1822） 蜗牛，以研究在各种植物类型和膳食碳酸盐含量下其软组织和排泄物的 δ13C。我们的结果表明，蜗牛主要吸收有机物 （OM），对膳食碳酸盐的使用有限。排泄物中有机物的 δ13C 与饮食中的有机物呈正相关，但由于同化过程中可变的碳同位素分馏而表现出偏差。组织 δ13C （δ13C组织） 与饮食中 OM 的 δ13C （δ13COM） 呈正相关，随周转率的变化而变化，周转率更快，如消化腺，表现出更多的负 δ13C 组织值。此外，组织和饮食之间的碳同位素分馏 （Δ13Ctissue-OM） 因植物类型而异。用 C3 植物喂养的蜗牛显示正 Δ13Ctissue-OM 值，而用 C4 植物喂养的蜗牛则显示负值。这些 Δ13Ctissue-OM 值在蜗牛快速生长的条件下远非平衡 （Δ13Ctissue-OM = 0）。我们的研究结果表明，用 C3 和 C4 植物喂养的蜗牛会导致不同的碳同位素分馏，导致植物与陆地蜗牛材料（例如，排泄物、组织、贝壳和贝壳结合的有机物）之间的 δ13C 偏差。提出了一种蜗牛碳代谢和同位素分馏的综合模型，包括从饮食到软组织和排泄的同化过程。 本研究强调了在解释陆地蜗牛材料的 δ13C 以进行古环境重建时，生长速率和周转率等生理因素的重要性。