Sinking particulate organic matter controls the flux of carbon (C) from the surface ocean to the deep sea. Microorganisms actively colonize particles, but the extent to which microbial metabolism influences particle export remains uncertain. We conducted experiments to quantify rates of bacterial production (derived based on ³H-leucine incorporation) and dark C-fixation (based on ¹⁴C-bicarbonate assimilation) associated with sinking particles collected from the base of the euphotic zone (175 m) in the subtropical North Pacific Ocean. Seawater was amended with sinking particles and rates of filter size-fractionated (0.2, 2, and 20 μm) bacterial production and dark C-fixation were measured. Sequencing of 16S ribosomal RNA (rRNA) gene amplicons revealed that microorganisms in the particle-amended treatments differed from those in the unamended seawater controls, with the particle treatments enriched in putative copiotrophic bacteria. The addition of sinking particles increased rates of bacterial production (by 6- to 9-fold), and to a lesser extent dark C-fixation (by 1.7- to 4.6-fold), relative to unamended controls, with most of the production associated with filter pore sizes < 20 μm. Normalizing production to concentrations of particulate C yielded rates that were statistically indistinguishable between particle-amended treatments and unamended controls. We then examined possible relationships between sinking particulate C flux attenuation and its supply to the mesopelagic waters, revealing that flux attenuation was positively related to increases in particulate C supply. Together with results from our experiments, we suggest processes that contribute to sinking particle disaggregation both increase flux attenuation and favor microbial mineralization of particle-derived organic matter.

中文翻译：

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北太平洋亚热带下沉颗粒相关微生物的产生和多样性

下沉的颗粒有机物控制着从表层海洋到深海的碳 (C) 通量。微生物积极定植颗粒，但微生物代谢影响颗粒出口的程度仍不确定。我们进行了实验，以量化细菌产生率（基于³ H-亮氨酸掺入）和暗 C 固定（基于¹⁴ C-碳酸氢盐同化）与从透光区底部（175 m）收集的下沉颗粒相关。亚热带北太平洋。用下沉颗粒和过滤器尺寸分级（0.2、2 和 20  μm) 测量细菌产生和暗 C 固定。对 16S 核糖体 RNA (rRNA) 基因扩增子的测序显示，粒子修正处理中的微生物与未修正海水对照中的微生物不同，粒子处理中富含假定的营养细菌。相对于未修正的对照，下沉颗粒的添加增加了细菌产生率（6 到 9 倍），并在较小程度上增加了暗 C 固定（1.7 到 4.6 倍），其中大部分产生相关过滤孔径 < 20  μ米。将生产标准化为颗粒 C 的浓度产生的速率在粒子修正处理和未修正控制之间在统计上无法区分。然后，我们检查了下沉微粒 C 通量衰减与其对中层水域的供应之间可能的关系，揭示通量衰减与微粒 C 供应的增加呈正相关。结合我们的实验结果，我们建议有助于下沉颗粒解聚的过程既增加通量衰减又有利于颗粒衍生的有机物质的微生物矿化。