Earthworms (Oligochaeta: Lumbricidae) have substantial effects on the structure and fertility of soils with consequences for the diversity of plant communities and associated ecosystem functions. However, we still lack a clear understanding of the functional role earthworms play in terrestrial ecosystems, partly because easy-to-use methods to quantify their activities are missing. In this study, we tested whether earthworms and their casts can be dual-labelled with 15N and 13C stable isotopes by cultivating them in soil substrate amended with 15N ammonium nitrate and 13C-glucose. Additionally, we also wanted to know whether (i) earthworms from different functional groups (soil-feeders vs. litter-feeders) and their casts would differ in their incorporation of stable isotopes, (ii) if enrichment levels are higher if the same amount of isotopes is applied in one dose or in staggered doses, and (iii) if isotopic enrichment in casts changes when they are stored in a conditioning cabinet or in a pot filled with soil placed in a greenhouse. Our findings show the feasibility of dual-labelling tissues and casts of both litter-feeding (Lumbricus terrestris) and soil-feeding (Aporrectodea caliginosa) earthworms using the same method. The advantage of this method is that earthworms and their casts can be labelled under realistic conditions by cultivating them for only four days in soil that received a one-time addition of commercially available stable isotopes instead of offering labelled plant material. In earthworms, the isotopic enrichment remained at a stable level for at least 21 days; labelled casts could be stored for at least 105 days without significantly decreasing their isotopic signals. This simple and efficient method opens new avenues for studying the role of these important ecosystem engineers in nutrient cycling and their functional relationships with other organisms.

中文翻译：

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蚯蚓不同功能群及其管型的稳定同位素 15N 和 13C 标记：研究营养关系的工具


蚯蚓（寡毛纲：蚓科）对土壤的结构和肥力具有重大影响，对植物群落的多样性和相关的生态系统功能产生影响。然而，我们仍然对蚯蚓在陆地生态系统中发挥的功能作用缺乏清晰的了解，部分原因是缺乏量化其活动的易于使用的方法。在这项研究中，我们通过在用 15N 硝酸铵和 13C-葡萄糖修正的土壤基质中培养蚯蚓及其铸件，测试是否可以用 15N 和 13C 稳定同位素对它们进行双重标记。此外，我们还想知道（i）来自不同功能类群（土壤饲养者与垃圾饲养者）的蚯蚓及其铸件在稳定同位素的掺入方面是否会有所不同，（ii）如果数量相同，富集水平是否更高的同位素以一次剂量或交错剂量施用，以及(iii)当将铸件储存在调节柜中或置于温室中的装满土壤的盆中时，铸件中的同位素富集是否发生变化。我们的研究结果表明，使用相同的方法对垃圾食性（Lumbricus terrestris）和土壤食性（Aporectodea caliginosa）蚯蚓的组织和管型进行双标记的可行性。这种方法的优点是，只需在一次性添加市售稳定同位素的土壤中培养蚯蚓及其管型四天，即可在现实条件下对蚯蚓及其管型进行标记，而不是提供标记的植物材料。在蚯蚓中，同位素富集保持在稳定水平至少 21 天；标记的管型可以保存至少 105 天，而不会显着降低其同位素信号。 这种简单而有效的方法为研究这些重要的生态系统工程师在养分循环中的作用及其与其他生物体的功能关系开辟了新的途径。