Carbon turnover in aquatic environments is dependent on biochemical properties of organic matter (OM) and its degradability by the surrounding microbial community. Non-additive interactive effects represent a mechanism where the degradation of biochemically persistent OM is stimulated by the provision of bioavailable OM to the degrading microbial community. Whilst this is well established in terrestrial systems, whether it occurs in aquatic ecosystems remains subject to debate. We hypothesised that OM from zooplankton carcasses can stimulate the degradation of biochemically persistent leaf material, and that this effect is influenced by the daphnia:leaf OM ratio and the complexity of the degrading microbial community. Fresh Daphnia magna carcasses and ¹³C-labelled maize leaves (Zea mays) were incubated at different ratios (1:1, 1:3 and 1:5) alongside either a complex microbial community (<50 µm) or solely bacteria (<0.8 µm). ¹³C stable-isotope measurements of CO₂ analyses were combined with phospholipid fatty acids (PLFA) analysis and DNA sequencing to link metabolic activities, biomass and taxonomic composition of the microbial community. Our experiments indicated a significantly higher respiration of leaf-derived C when daphnia-derived OM was most abundant (i.e. daphnia:leaf OM ratio of 1:1). This process was stronger in a complex microbial community, including eukaryotic microorganisms, than a solely bacterial community. We concluded that non-additive interactive effects were a function of increased C–N chemodiversity and microbial complexity, with the highest net respiration to be expected when chemodiversity is high and the degrading community complex. This study indicates that identifying the interactions and processes of OM degradation is one important key for a deeper understanding of aquatic and thus global carbon cycle.

水生环境中的碳周转取决于有机物 (OM) 的生化特性及其周围微生物群落的降解性。非加性交互作用代表了一种机制，其中通过向降解微生物群落提供生物可利用的 OM 来刺激生化持久性 OM 的降解。虽然这在陆地系统中已得到充分证实，但它是否发生在水生生态系统中仍然存在争议。我们假设来自浮游动物尸体的 OM 可以刺激生化持久性叶子材料的降解，并且这种效应受到水蚤：叶子 OM 比率和降解微生物群落复杂性的影响。将新鲜的大型水蚤尸体和¹³ C 标记的玉米叶 ( Zea mays)以不同的比例（1:1、1:3 和 1:5）与复杂的微生物群落（<50 µm）或单独的细菌（<0.8微米）。_{CO 2分析的}¹³ C 稳定同位素测量与磷脂脂肪酸 (PLFA) 分析和 DNA 测序相结合，将微生物群落的代谢活动、生物量和分类组成联系起来。我们的实验表明，当水蚤来源的 OM 最丰富时（即水蚤：叶 OM 比例为 1:1），叶源 C 的呼吸作用显着较高。这个过程在复杂的微生物群落（包括真核微生物）中比在单独的细菌群落中更强。我们得出的结论是，非加性相互作用效应是 C-N 化学多样性和微生物复杂性增加的函数，当化学多样性高且降解群落复杂时，预计净呼吸量最高。这项研究表明，确定有机物质降解的相互作用和过程是深入了解水生乃至全球碳循环的重要关键。