Earthworms are invading soil communities worldwide, and their actions as decomposers and ecosystem engineers are vastly impacting many ecosystem functions. In the northern regions of North America, invasive earthworms are often functionally distinct from the native invertebrate fauna and, thus, typically occupy empty trophic niches in soil food webs. Nevertheless, they can affect the co-occurring soil invertebrate communities in multiple indirect ways. Particularly, the redistribution and removal of litter resources can affect feeding interactions of soil biota that channel up to higher trophic levels, such as predators, causing shifts across all components of the soil food web, which are hard to investigate. To study trophic shifts in earthworm-invaded soil communities, we used ground predators as model organisms since they occupy high trophic levels and connect different energy channels in soil food webs. We used stable isotope (¹³C and ¹⁵N) and fatty acid analyses as complementary tools to describe the trophic levels and basal resources of consumers that were impacted by earthworm invasion, specifically examining the trophic niches and resources available to ground-dwelling invertebrates of a northern aspen forest. The distinct trophic niches of invertebrate species were affected significantly by earthworm invasion. Shifts in neutral lipid fatty acid profiles as well as decreases in animal Δ¹³C and Δ¹⁵N signatures indicated changes in basal resources and trophic levels, respectively. Furthermore, we observed a trend of greater intra-specific and less inter-specific variation in fatty acid profiles of soil organisms following earthworm invasion. Notably, shifts in marker fatty acids of ground-dwelling invertebrates were opposite to the changes observed in soil microbial communities, suggesting de-coupling of soil microbial and ground arthropod food-web compartments. Overall, our study revealed a systemic effect of invasive earthworms on ground-dwelling invertebrates. Earthworms presumably consumed a considerable amount of resources, such as litter and, thus, incorporated them in the soil food web, which was, as a basal resource, not available in the food web free of earthworms. Overall, the ground-dwelling invertebrates have adapted (changed their trophic function) which could explain the balancing of potential environmental changes that are caused by invasive earthworms. This observation potentially explains why these species are dominant in the studied forest and resist earthworm invasion. Future studies should investigate if altered litter availability also causes shifts in soil biodiversity in invaded forests, which is assumed but rarely directly tested to date.

蚯蚓正在入侵世界各地的土壤群落，它们作为分解者和生态系统工程师的行为正在极大地影响许多生态系统功能。在北美北部地区，侵入性蚯蚓通常在功能上与本地无脊椎动物区系不同，因此通常占据土壤食物网中的空营养生态位。然而，它们可以以多种间接方式影响同时发生的土壤无脊椎动物群落。特别是，垃圾资源的重新分配和清除会影响土壤生物群的摄食相互作用，这些生物群会引导到更高的营养水平，例如捕食者，导致土壤食物网的所有组成部分发生变化，这很难调查。为了研究蚯蚓入侵土壤群落的营养变化，我们使用地面捕食者作为模式生物，因为它们占据高营养水平并连接土壤食物网中的不同能量通道。我们使用稳定同位素 (¹³ C 和¹⁵ N) 和脂肪酸分析作为补充工具来描述受蚯蚓入侵影响的消费者的营养水平和基础资源，特别是检查北部白杨林的地栖无脊椎动物可利用的营养生态位和资源。蚯蚓入侵显着影响了无脊椎动物物种独特的营养生态位。中性脂质脂肪酸谱的变化以及动物 Δ ¹³ C 和 Δ ^15的降低N 个签名分别表示基础资源和营养水平的变化。此外，我们观察到蚯蚓入侵后土壤生物的脂肪酸谱出现更大的种内变化和更少种间变化的趋势。值得注意的是，地面无脊椎动物的标记脂肪酸的变化与土壤微生物群落中观察到的变化相反，这表明土壤微生物和地面节肢动物的食物网区室是脱钩的。总体而言，我们的研究揭示了侵入性蚯蚓对地面无脊椎动物的系统性影响。蚯蚓可能消耗了大量的资源，例如垃圾，因此将它们纳入土壤食物网，作为一种基础资源，在没有蚯蚓的食物网中是不可用的。全面的，地栖无脊椎动物已经适应（改变了它们的营养功能），这可以解释由入侵蚯蚓引起的潜在环境变化的平衡。这一观察结果可能解释了为什么这些物种在所研究的森林中占主导地位并抵抗蚯蚓入侵。未来的研究应该调查是否改变枯枝落叶的可用性也会导致被入侵森林中土壤生物多样性的变化，这是假设的，但迄今为止很少直接测试。