Soil microarthropods are essential for nutrient cycling in forest ecosystems as they are integral components of decomposer food webs. They channel carbon and nutrients from leaf litter and roots to higher trophic levels; however, knowledge on the relative importance of different channels and on their variation with forest type is lacking. Although the importance of root‐derived inputs for sustaining soil food webs is increasingly recognized, the pathways by which they are channeled to higher trophic levels are little understood. For the channeling, ectomycorrhizal fungi may play a significant role, but until now methods allowing to separate the contribution of ectomycorrhizal and saprotrophic fungi to the nutrition of soil animal communities are lacking. Using dual analysis of ¹⁵N and ¹³C in amino acids (AAs), we investigated trophic positions and basal resources of two major groups of soil microarthropods, Collembola and Oribatida, in beech and spruce forests in Germany. By applying a ¹³C fingerprinting approach and Bayesian mixing models, we separated in a first step the relative contribution of bacteria, fungi, and plants to the nutrition of soil microarthropods. As fungi were identified as the major food source, in a second step we attempted to separate the contribution of ectomycorrhizal vs. saprotrophic fungi. For the first time, we provide direct evidence that soil microarthropods mainly rely on saprotrophic fungi, whereas ectomycorrhizal fungi are consumed by only few species. While trophic niches of Collembola and Oribatida species generally varied little between beech and spruce forests, plant detritus as basal resource of soil microarthropods was somewhat more important in beech forests, whereas in spruce forests microbial resources dominated. Overall, the dual analysis of carbon and nitrogen in AAs provided insight into food web structure of soil microarthropods in unprecedented detail, and for the first time allowed to estimate the relative importance of mycorrhizal and saprotrophic fungi for soil food web nutrition, a long‐standing riddle in soil food web ecology. The technique provides the perspective for a comprehensive understanding of the trophic structure and energy channeling in soil food webs.

中文翻译：

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氨基酸的稳定同位素表明土壤分解者微节肢动物主要以腐生真菌为食

土壤微节肢动物对于森林生态系统中的养分循环至关重要，因为它们是分解者食物网的组成部分。它们将碳和营养物从叶凋落物和根中引导到更高的营养水平；但是，缺乏有关不同渠道的相对重要性及其随森林类型变化的知识。尽管越来越多地认识到根源输入对维持土壤食物网的重要性，但人们很少了解将根源输入传递到较高营养水平的途径。对于引导作用，外生菌根真菌可能起着重要的作用，但是直到现在，仍缺乏将外生菌根和腐生真菌对土壤动物群落营养的贡献分开的方法。使用¹⁵ N和^13的双重分析氨基酸（AAs）中的C，我们调查了德国山毛榉和云杉林中两大类土壤节肢动物节肢动物节肢动物（Collembola和Oribatida）的营养位置和基础资源。通过应用¹³利用C指纹图谱方法和贝叶斯混合模型，我们首先分离了细菌，真菌和植物对土壤微节肢动物营养的相对贡献。由于真菌被确定为主要食物来源，因此在第二步中，我们试图分离外生菌根菌和腐生菌的作用。我们首次提供直接的证据，证明土壤节肢动物主要依靠腐生真菌，而外生菌根真菌仅被少数物种消耗。Collembola和Oribatida物种的营养位通常在山毛榉森林和云杉林之间变化不大，而作为土壤微节肢动物基础资源的植物碎屑在山毛榉森林中则更为重要，而在云杉林中，微生物资源占主导地位。全面的，AA中碳和氮的双重分析为土壤微节肢动物的食物网结构提供了前所未有的见解，并且首次使人们能够估计菌根和腐生真菌对土壤食物网营养的相对重要性，这是长期存在的难题。土壤食物网生态学。该技术为全面理解土壤食物网中的营养结构和能量通道提供了前景。