Carbon fractionation (Δ¹³C) is well documented for various plants functional types. Yet, specific studies on Δ¹³C on mangroves are particularly rare although they have a key role in coastal carbon (C) cycling. In this study, we investigated the ¹³C exchanges between leaves and the atmosphere and between the main plant’s organs in two common mangroves species, Avicennia marina and Rhizophora stylosa subjected to two different CO₂ concentrations. Two-years-old saplings were grown in mesocosms during one year under 400 ppm and 800 ppm of CO₂. At the end of the experiment, the isotopic value of the night-respired CO₂ was measured on six individuals for each species and CO₂ treatment. Then, 60 saplings were harvested to measure the organs δ¹³C values, and, finally, carbon fractionation (Δ¹³C) during photosynthesis, post-photosynthesis and apparent Δ¹³C during night respiration were calculated. Results indicated that elevated CO₂ reduced Δ¹³C during photosynthesis by 13% and during night respiration by 20%. Alongside, within-plant Δ¹³C was twice higher in the saplings grown under elevated CO₂ concentrations. These results showed that ongoing and future increases in atmospheric CO₂ concentrations have the potential to modify the δ¹³C values of mangrove trees. These results could have important implications in Blue Carbon sciences, and particularly in the comprehension of future carbon cycling in coastal wetlands, mangroves being an essential link in terrestrial and marine food webs along tropical and subtropical coastlines.

各种植物功能类型的碳分馏 (Δ ¹³ C) 有据可查。然而，对红树林的Δ ¹³ C 的具体研究特别罕见，尽管它们在沿海碳 (C) 循环中具有关键作用。在这项研究中，我们调查了两种常见红树林物种Avicennia marina和Rhizophora stylosa 的叶子和大气之间以及主要植​​物器官之间的¹³ C 交换，这些物种受到两种不同 CO ₂浓度的影响。在两年内，在400 ppm和800 ppm CO _2的环境中生长了两岁的树苗。实验结束时，夜间呼吸的 CO ₂同位素值对每个物种和 CO ₂处理的六个个体进行测量。然后，收获60棵树苗测量器官δ ¹³ C值，最后计算光合作用、光合作用后和夜间呼吸过程中的表观Δ ¹³ C的碳分馏(Δ ¹³ C) 。结果表明，升高的 CO ₂使光合作用期间的Δ ¹³ C减少了 13%，夜间呼吸期间减少了 20%。此外，在升高的 CO ₂浓度下生长的树苗的植物内 Δ ¹³ C 高两倍。这些结果表明，大气 CO _{2 的}持续增加和未来增加浓度有可能改变红树林的 δ ¹³ C 值。这些结果可能对蓝碳科学具有重要意义，特别是在理解沿海湿地未来的碳循环方面，红树林是热带和亚热带海岸线上陆地和海洋食物网的重要环节。