The association between corals and photosynthetic dinoflagellates is one of the most well-known nutritional symbioses, but nowadays it is threatened by global changes. Nutritional exchanges are critical to understanding the performance of this symbiosis under stress conditions. Here, compound-specific δ¹⁵N and δ¹³C values of amino acids (δ¹⁵N_AA and δ¹³C_AA) were assessed in autotrophic, mixotrophic and heterotrophic holobionts as diagnostic tools to follow nutritional interactions between the partners. Contrary to what was expected, heterotrophy was mainly traced through the δ¹⁵N of the symbiont’s amino acids (AAs), suggesting that symbionts directly profit from host heterotrophy. The trophic index (TP) ranged from 1.1 to 2.3 from autotrophic to heterotrophic symbionts. In addition, changes in TP across conditions were more significant in the symbionts than in the host. The similar δ¹³C-AAs signatures of host and symbionts further suggests that symbiont-derived photosynthates are the main source of carbon for AAs synthesis. Symbionts, therefore, appear to be a key component in the AAs biosynthetic pathways, and might, via this obligatory function, play an essential role in the capacity of corals to withstand environmental stress. These novel findings highlight important aspects of the nutritional exchanges in the coral–dinoflagellates symbiosis. In addition, they feature δ¹⁵N_AA as a useful tool for studies regarding the nutritional exchanges within the coral–symbiodiniaceae symbiosis.

中文翻译：

---

使用特定于氨基酸化合物的稳定同位素分析追踪珊瑚-鞭毛虫共生的营养可塑性

珊瑚与光合鞭毛藻之间的联系是最著名的营养共生体之一，但如今它正受到全球变化的威胁。营养交流对于了解这种共生在压力条件下的表现至关重要。在此，化合物特异性δ ¹⁵ N和δ ¹³个氨基酸的C值（δ ¹⁵ Ñ _AA和δ ¹³ C ^ _AA）的自养，混合营养和异holobionts被评定为诊断工具跟随伙伴之间的营养相互作用。出乎预料的东西，异养主要是通过δ追溯到¹⁵N共生体的氨基酸（AAs）中的N，表明共生体直接受益于宿主异养。营养指数（TP）从自养型到异养型共生体范围从1.1到2.3。此外，共生体中跨条件的TP变化比宿主更显着。类似的δ ¹³主机和共生体进一步的C-AA的签名表明，共生体衍生的光合是碳为AA的合成的主要来源。因此，共生体似乎是AA生物合成途径中的关键组成部分，并可能通过这种强制性功能在珊瑚抵抗环境压力的能力中发挥重要作用。这些新颖的发现突出了珊瑚－鞭毛虫共生中营养交换的重要方面。另外，它们具有δ¹⁵ N _AA是研究珊瑚-共生植物共生关系中营养交换的有用工具。