Terrestrial carbon cycling is largely mediated by soil food webs. Identifying the carbon source for soil animals has been desired to distinguish their roles in carbon cycling, but it is challenging for small invertebrates at low trophic levels because of methodological limitations. Here, we combined radiocarbon (¹⁴C) analysis with stable isotope analyses (¹³C and ¹⁵N) to understand feeding habits of soil microarthropods, especially focusing on springtail (Collembola). Most Collembola species exhibited lower Δ¹⁴C values than litter regardless of their δ¹³C and δ¹⁵N signatures, indicating their dependence on young carbon. In contrast with general patterns across all taxonomic groups, we found a significant negative correlation between δ¹⁵N and Δ¹⁴C values among the edaphic Collembola. This means that the species with higher δ¹⁵N values depend on C from more recent photosynthate, which suggests that soil-dwelling species generally feed on mycorrhizae to obtain root-derived C. Many predatory taxa exhibited higher Δ¹⁴C values than Collembola but lower than litter, indicating non-negligible effects of collembolan feeding habits on the soil food web. Our study demonstrated the usefulness of radiocarbon analysis, which can untangle the confounding factors that change collembolan δ¹⁵N values, clarify animal feeding habits and define the roles of organisms in soil food webs.

陆地碳循环主要由土壤食物网介导。一直希望确定土壤动物的碳源以区分它们在碳循环中的作用，但由于方法上的限制，对于低营养水平的小型无脊椎动物来说具有挑战性。在这里，我们将放射性碳 ( ¹⁴ C) 分析与稳定同位素分析 ( ¹³ C 和¹⁵ N) 相结合，以了解土壤微型节肢动物的摄食习性，尤其关注跳尾虫 (Colembola)。大多数跳虫物种的 Δ ¹⁴ C 值低于枯枝落叶，无论它们的δ ¹³ C 和δ ¹⁵N 签名，表明它们对年轻碳的依赖。与所有分类群的一般模式相比，我们发现土壤跳虫中的δ ¹⁵ N 和 Δ ^{14 C 值之间存在显着的负相关。}这意味着具有较高δ ¹⁵ N 值的物种依赖于来自最近光合产物的 C，这表明土壤栖息物种通常以菌根为食以获得根源 C。许多捕食性分类群表现出较高的 Δ ¹⁴C 值低于跳虫但低于枯枝落叶，表明跳虫摄食习惯对土壤食物网的影响不可忽略。我们的研究证明了放射性碳分析的有用性，它可以解开改变跳虫δ ¹⁵ N 值的混杂因素，阐明动物的摄食习惯并确定有机体在土壤食物网中的作用。