The effects of single macrofauna taxa on benthic nitrogen (N) cycling have been extensively studied, whereas how macrofaunal communities affect N-related processes remains poorly explored. In this study, we characterized benthic N-cycling in bioturbated sediments of the oligotrophic Öre Estuary (northern Baltic Sea). Solute fluxes and N transformations (N₂ fixation, denitrification and dissimilative nitrate reduction to ammonium [DNRA]) were measured in sediments and macrofauna-associated microbes (holobionts) to partition the role of three dominant taxa (the filter feeder Limecola balthica, the deep deposit feeder Marenzelleria spp., and the surface deposit feeder Monoporeia affinis) in shaping N-cycling. In the studied area, benthic macrofauna comprised a low diversity community with dominance of the three taxa, which are widespread and dominant in the Baltic. The biomass of these taxa in macrofaunal community explained up to 30% of variation in measured biogeochemical processes, confirming their important role in ecosystem functioning. The results also show that these taxa significantly contributed to the benthic metabolism and N-cycling (direct effect) as well as to sediments bioturbation with positive feedback to dissimilative nitrate reduction (indirect effect). Taken together, these functions promoted a reuse of nutrients at the benthic level, limiting net losses (e.g. denitrification) and effluxes to bottom water. Finally, the detection of multiple N transformations in macrofauna holobionts suggested a community-associated versatile microbiome, however, its role was of minor importance as compared to the activity of sediment-associated microbial communities. The present study highlights hidden and interactive effects among microbes and macrofauna, which should be considered analysing benthic functioning.

单个大型动物分类群对底栖氮 (N) 循环的影响已得到广泛研究，而大型动物群落如何影响 N 相关过程的研究仍然很少。在这项研究中，我们描述了贫营养厄勒河口（波罗的海北部）的生物扰动沉积物中的底栖氮循环。溶质通量和N变换（N ₂中沉积物和大型动物相关的微生物（holobionts）测量固定，反硝化作用和dissimilative硝酸盐还原成铵[DNRA]）进行分区3个优势种类（所述过滤器供给器的作用Limecola balthica，深沉积物饲养者Marenzelleria spp. 和表面沉积物饲养者Monoporeia affinis) 形成 N 循环。在研究区域，底栖大型动物群落组成了一个低多样性群落，其中三个类群占主导地位，这三个类群在波罗的海广泛分布并占主导地位。大型动物群落中这些分类群的生物量解释了测量的生物地球化学过程中高达 30% 的变化，证实了它们在生态系统功能中的重要作用。结果还表明，这些分类群对底栖代谢和氮循环（直接效应）以及沉积物生物扰动有显着贡献，对异化硝酸盐还原具有正反馈（间接效应）。总之，这些功能促进了底栖层面养分的再利用，限制了净损失（例如反硝化作用）和向底水的流出。最后，在大型动物群落中检测到多个 N 转化表明了一个与群落相关的多功能微生物组，然而，与沉积物相关微生物群落的活动相比，它的作用并不重要。本研究强调了微生物和大型动物之间隐藏的和相互作用的影响，应考虑分析底栖功能。