The influence of diet on the δ13C of shell carbon in the pulmonate snail Helix aspersa
The influence of diet on the δ13C of shell carbon in the pulmonate snail Helix aspersa
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DOI：
10.1016/s0012-821x(01)00585-4
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发表时间：
2002-02
影响因子：
5.3
通讯作者：
L. Stott
中科院分区：
文献类型：
--
作者：
L. Stott
研究了饵料和大气CO2对实验室养殖的肺螺H.aspersa壳体文石和壳体结合有机碳碳同位素组成的影响。三组不同的蜗牛分别在长叶莴苣（C3植物，δ 13 C =−25.8‰）、玉米（C4植物，δ 13 C =−10.5‰）和酸橙子（富含12 C的C3植物，δ 13 C =−39.1‰）上饲养。如前所述，身体组织的同位素组成密切跟踪蜗牛饮食的同位素组成。然而，从文石壳中提取的酸不溶性有机基质的同位素组成并不跟踪所有组的饮食。在喂食玉米的蜗牛中，有机基质的同位素组成比身体负5‰，而在喂食C3植物材料的蜗牛中，基质比身体组织重约1‰。这些结果表明，同位素组成的有机基质碳不能作为同位素基板的古饮食重建没有首先确定的碳源和任何相关的分馏。在各养殖组中，贝壳文石的同位素组成相对于身体组织偏移12.3‰。这种抵消是不受碳酸盐的消费，是不是由于大气中的CO2扩散到血淋巴。壳文石的碳同位素组成最好的解释在平衡分馏与代谢CO2和HCO3之间的交换在血淋巴和分馏与碳酸盐沉淀。这些结果与以前的研究不同，以前的研究主要基于在野外收集的样本，这些研究表明大气中的二氧化碳对贝壳δ 13 C的贡献很大。培养结果表明，文石的δ 13 C是螺体组织同位素组成的良好记录物，因此比不溶性壳有机碳更能反映螺体组织的食性。由于蜗牛体内碳同位素的系统分馏是温度依赖性的，因此壳的δ 13 C可以提供一种独立的技术来估计古温度变化。
The influence of diet and atmospheric CO2on the carbon isotope composition of shell aragonite and shell-bound organic carbon in the pulmonate snail Helix aspersa raised in the laboratory was investigated. Three separate groups of snails were raised on romaine lettuce (C3 plant, δ13C=−25.8‰), corn (C4 plant, δ13C=−10.5‰), and sour orange (12C-enriched C3 plant, δ13C=−39.1‰). The isotopic composition of body tissues closely tracked the isotopic composition of the snail diet as demonstrated previously. However, the isotopic composition of the acid insoluble organic matrix extracted from the aragonite shells does not track diet in all groups. In snails that were fed corn the isotopic composition of the organic matrix was more negative than the body by as much as 5‰ whereas the matrix was approximately 1‰ heavier than the body tissues in snails fed a diet of C3 plant material. These results indicate that isotopic composition of the organic matrix carbon cannot be used as an isotopic substrate for paleodietary reconstructions without first determining the source of the carbon and any associated fractionations. The isotopic composition of the shell aragonite is offset from the body tissues by 12.3‰ in each of the culture groups. This offset was not influenced by the consumption of carbonate and is not attributable to the diffusion of atmospheric CO2into the hemolymph. The carbon isotopic composition of shell aragonite is best explained in terms of equilibrium fractionations associated with exchange between metabolic CO2and HCO3in the hemolymph and the fractionation associated with carbonate precipitation. These results differ from previous studies, based primarily on samples collected in the field, that have suggested atmospheric carbon dioxide contributes significantly to the shell δ13C. The culture results indicate that the δ13C of aragonite is a good recorder of the isotopic composition of the snail body tissue, and therefore a better recorder of diet than is the insoluble shell organic carbon. Because the systematic fractionation of carbon isotopes within the snail is temperature dependent, the δ13C of the shell could provide an independent technique for estimating paleotemperature changes.