The ¹³C/¹²C ratio of C₃ plant matter is thought to be controlled by the isotopic composition of atmospheric CO₂ and stomatal response to environmental conditions, particularly mean annual precipitation (MAP). The effect of CO₂ concentration on ¹³C/¹²C ratios is currently debated, yet crucial to reconstructing ancient environments and quantifying the carbon cycle. Here we compare high-resolution ice core measurements of atmospheric CO₂ with fossil plant and faunal isotope records. We show the effect of pCO₂ during the last deglaciation is stronger for gymnosperms (-1.4 ± 1.2‰) than angiosperms/fauna (-0.5 ± 1.5‰), while the contributions from changing MAP are -0.3 ± 0.6‰ and -0.4 ± 0.4‰, respectively. Previous studies have assumed that plant ¹³C/¹²C ratios are mostly determined by MAP, an assumption which is sometimes incorrect in geological time. Atmospheric effects must be taken into account when interpreting terrestrial stable carbon isotopes, with important implications for past environments and climates, and understanding plant responses to climate change.

中文翻译：

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大气二氧化碳对陆地化石档案稳定碳同位素组成的影响。

_{C 3}植物物质的13 C/ ¹² C 比率被认为是由大气CO ₂的同位素组成和气孔对环境条件（特别是年平均降水量（MAP））的响应^控制。_{CO 2}浓度对¹³ C/ ¹² C 比率的影响目前存在争议，但对于重建古代环境和量化碳循环至关重要。_{在这里，我们将大气 CO 2}的高分辨率冰芯测量值与化石植物和动物同位素记录进行比较。我们发现末次冰消期期间 pCO 2 对裸子植物的影响 (-1.4 ± 1.2 ‰) 比被子植物/动物群 (-0.5 ± 1.5 ‰) 更强，而改变 MAP 的贡献为 -0.3 ± 0.6 ‰ 和_-0.4 ±分别为0.4‰。先前的研究假设植物¹³ C/ ¹² C 比率主要由 MAP 决定，这种假设在地质年代有时是不正确的。在解释陆地稳定碳同位素时必须考虑大气影响，这对过去的环境和气候以及了解植物对气候变化的反应具有重要影响。