Abstract According to the River Continuum Concept, headwater streams are richer in allochthonous (e.g. terrestrial leaves) than autochthonous (e.g. algae) sources of organic matter for consumers. However, compared to algae, leaf litter is of lower food quality, particularly ω‐3 polyunsaturated fatty acids (n‐3 PUFA), and would constrain the somatic growth, maintenance, and reproduction of stream invertebrates. It may be thus assumed that shredders, such as Gammarus, receive lower quality diets than grazers, e.g. Ecdyonurus, that typically feed on algae. The objective of this study was to assess the provision of dietary PUFA from leaf litter and algae to the shredder Gammarus and the grazer Ecdyonurus. Three different diets (algae, terrestrial leaves, and an algae–leaf litter mix) were supplied to these macroinvertebrates in a flume experiment for 2 weeks. To differentiate how diet sources were retained in these consumers, algae were isotopically labelled with 13C. Both consumers became enriched with 13C in all treatments, demonstrating that both assimilated algae. For Gammarus, n‐3 PUFA increased, whereas n‐6 PUFA stayed constant. By contrast, the n‐3 PUFA content of Ecdyonurus decreased as a consequence of declining algal supply. Results from compound‐specific stable isotope analysis provided evidence that the long‐chain n‐3 PUFA eicosapentaenoic acid (EPA) in both consumers was more enriched in 13C than the short‐chain n‐3 PUFA α‐linolenic acid, suggesting that EPA was taken up directly from algae and not from heterotrophic biofilms on leaf litter. Both consumers depended on algae as their carbon and EPA source and retained their EPA from high‐quality algae.

中文翻译：

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在底栖无脊椎动物中优先保留藻类碳：来自室外水槽实验的稳定同位素和脂肪酸证据

摘要 根据河流连续统概念，源头溪流中的外来（例如陆地叶子）比本地（例如藻类）有机物质来源对消费者而言更为丰富。然而，与藻类相比，落叶的食物质量较低，尤其是 ω-3 多不饱和脂肪酸 (n-3 PUFA)，会限制溪流无脊椎动物的体细胞生长、维持和繁殖。因此可以假设碎纸机（例如 Gammarus）接受的饲料质量低于通常以藻类为食的食草动物（例如 Ecdyonurus）。本研究的目的是评估从落叶和藻类中向碎纸机 Gammarus 和食草动物 Ecdyonurus 提供的膳食 PUFA。三种不同的饮食（藻类、陆生叶子、在水槽实验中向这些大型无脊椎动物提供了藻类-树叶混合物），持续了 2 周。为了区分这些消费者的饮食来源是如何保留的，藻类被同位素标记为 13C。两位消费者在所有处理中都富含 13C，表明两者都同化了藻类。对于 Gammarus，n-3 PUFA 增加，而 n-6 PUFA 保持不变。相比之下，蜕皮动物的 n-3 PUFA 含量由于藻类供应减少而减少。化合物特定的稳定同位素分析结果提供的证据表明，两个消费者的长链 n-3 PUFA 二十碳五烯酸 (EPA) 比短链 n-3 PUFA α-亚麻酸更富含 13C，表明 EPA 是直接从藻类吸收，而不是从凋落物上的异养生物膜吸收。