Dual amino acid stable isotope analyses (13C and 15N) as a novel method to unravel energy fluxes and trophic relationships in soil animal food webs

土壤动物食物网是一个复杂的异质系统。尽管它们对生态系统的功能发挥着根本作用，但其中的基本过程并没有得到很好的理解。真菌、细菌和植物来源资源之间的区分、能量通量的量化以及营养水平的估计仍然是主要的挑战。基于从大量稳定同位素和化合物特定脂肪酸分析中获得的结果，拟议项目旨在调整动物和资源中单个氨基酸（AAs）的13 C和15 N特征分析，以分析土壤动物食物网。特定化合物分析的AA提供了显着的优势，散装同位素签名的分析，规避问题，如同位素变化的基础资源和不同的营养分馏。通过利用一个生物体内所谓的营养和源AA的15 N特征，可以明确地识别营养水平，而不依赖于不同的基线。13 C签名的基本AA可以用来区分能量通量来源于不同的基础资源，使用稳定的同位素指纹。植物、真菌和细菌在AA合成的代谢途径上不同，因此产生独特的13 C模式，并转移给消费者。基础资源的相对贡献可以使用混合模型来量化。13 C和15 N分析的AA相结合是一种新奇的食物网分析，但很少有研究采用这种方法。为了适应土壤动物食物网中氨基酸的双重分析，我将进行对照实验室实验，以建立营养富集因子（TEFs）的个别AAs，并调查生理参数，如AAs在土壤动物中的半衰期，和饮食质量对TEFs的影响。混合饮食喂养实验将允许开发混合模型，以量化从基础资源到消费者的相对能量通量。在一个以分解有机体的主要群体为特征的围隔生态系统标记实验中，我将利用AA的双重同位素分析来分离地上与地下资源的贡献，同时通过真菌/细菌/植物通道量化通量。AA的双同位素分析代表了一种新的和非常有前途的方法，以前所未有的详细阐明土壤动物食物网的营养结构。

Soil animal food webs are complex and heterogeneous systems. Despite their fundamental role for ecosystem functioning, basic processes therein are not well understood. Differentiation between fungal, bacterial and plant derived resources, quantification of energy fluxes as well as estimation of trophic levels remain major challenges. Building on findings gained from bulk stable isotope and compound-specific fatty acid analyses, the proposed project aims at adapting the analysis of 13C and 15N signatures of individual amino acids (AAs) in animals and resources for analyzing soil animal food webs. Compound-specific analysis of AAs provides significant advantages over the analysis of bulk isotopic signatures, circumventing problems such as isotopic variation of basal resources and varying trophic fractionation. By utilizing 15N signatures of so-called trophic and source AAs within one organism, trophic levels can be unambiguously identified independently of differing baselines. 13C signatures of essential AAs can be used to distinguish between energy fluxes originating from different basal resources using stable isotope fingerprinting. Plants, fungi and bacteria differ in metabolic pathways of AA synthesis and therefore produce unique 13C patterns that are transferred to consumers. Relative contributions of basal resources can be quantified using mixing models. The combination of 13C and 15N analyses of AAs is a novelty for food web analyses; as yet very few studies adopted this approach. To adapt the dual analysis of AAs for soil animal food webs, I will conduct controlled laboratory experiments to establish trophic enrichment factors (TEFs) for individual AAs, and to investigate physiological parameters such as the half-life of AAs in soil animals, and the influence of diet quality on TEFs. Feeding experiments with mixed diets will allow developing mixing models to quantify relative energy fluxes from basal resources to consumers. In a mesocosm labeling experiment featuring major groups of decomposer organisms, I will utilize the dual isotopic analysis of AAs to separate contributions of aboveground vs. belowground resources, and at the same time quantify fluxes via fungal/bacterial/plant channels. The dual isotopic analysis of AAs represents a novel and very promising approach to clarify the trophic structure of soil animal food webs in unprecedented detail.