Antimicrobials, such as fungicides and antibiotics, pose a risk for microbial decomposers (i.e., bacteria and aquatic fungi) and invertebrate detritivores (i.e., shredders) that play a pivotal role in the ecosystem function of leaf litter breakdown. Although waterborne toxicity and diet-related effects (i.e., dietary exposure and microorganism-mediated alterations in food quality for shredders) of fungicides and antibiotics on decomposer-detritivore systems have been increasingly documented, their joint effect is unknown. We therefore assessed waterborne and dietary effects of an antimicrobial mixture consisting of the fungicide azoxystrobin (AZO) and the antibiotic ciprofloxacin (CIP) on microbial decomposers and the shredder Gammarus fossarum using a tiered approach. We compared effect sizes measured in the present study with model predictions (i.e., independent action) based on published data. During a 7-day feeding activity assay quantifying waterborne toxicity in G. fossarum, the leaf consumption of gammarids was reduced by ∼60 % compared to the control when subjected to the mixture at concentrations of each component causing a 20 % reduction in the same response variable when applied individually. Moreover, the selective feeding of gammarids during the food choice assay indicated alterations in food quality induced by the antimicrobial mixture. The food selection and, in addition, the decrease in microbial leaf decomposition is likely linked to changes in leaf-associated bacteria and fungi. During a long-term assay, energy processing, growth and energy reserves of gammarids were increased in presence of 15 and 500 μg/L of AZO and CIP, respectively, through the dietary pathway. These physiological responses were probably driven by CIP-induced alterations in the gut microbiome or immune system of gammarids. In general, model predictions matched observed effects caused by waterborne exposure on the leaf consumption, energy processing and growth of gammarids during short- and long-term assays, respectively. However, when complex horizontal (bacteria and aquatic fungi) and vertical (leaf-associated microorganisms and shredders) interactions were involved, model predictions partly over- or underestimated mixture effects. Therefore, the present study identifies uncertainties of mixture effect predictions for complex biological systems calling for studies targeting the underlying processes and mechanisms.

杀菌剂和抗生素等抗菌剂对微生物分解者（即细菌和水生真菌）和无脊椎动物碎食者（即粉碎者）构成风险，而它们在叶凋落物分解的生态系统功能中发挥着关键作用。尽管杀菌剂和抗生素对分解者-食腐动物系统的水传播毒性和饮食相关影​​响（即饮食暴露和微生物介导的碎纸机食品质量改变）已被越来越多地记录，但它们的共同影响尚不清楚。因此，我们采用分层方法评估了由杀菌剂嘧菌酯 (AZO) 和抗生素环丙沙星 (CIP) 组成的抗菌混合物对微生物分解剂和粉碎机Gammarus fossarum的水传播和饮食影响。我们将本研究中测量的效应大小与基于已发表数据的模型预测（即独立行动）进行了比较。在量化G. fossarum水源毒性的 7 天摄食活动测定中，当以每种成分的浓度进行混合物处理时，与对照相比，伽马的叶子消耗量减少了约 60 %，导致相同反应减少 20 %单独应用时变量。此外，在食物选择测定过程中对伽马病毒的选择性喂养表明抗菌混合物引起了食物质量的改变。此外，食物的选择以及微生物叶子分解的减少可能与叶子相关细菌和真菌的变化有关。在长期测定中，通过饮食途径，分别在 15 和 500 μg/L 的 AZO 和 CIP 存在下，伽马的能量处理、生长和能量储备得到增加。 这些生理反应可能是由 CIP 引起的肠道微生物组或伽马免疫系统的变化驱动的。一般来说，模型预测分别与在短期和长期分析中观察到的水性暴露对叶片消耗、能量处理和伽马科生长的影响相匹配。然而，当涉及复杂的水平（细菌和水生真菌）和垂直（叶相关微生物和粉碎机）相互作用时，模型预测部分高估或低估了混合效应。因此，本研究确定了复杂生物系统混合效应预测的不确定性，需要针对潜在过程和机制的研究。