Effect of increased pCO2 on bacterial assemblage shifts in response to glucose addition in Fram Strait seawater mesocosms

Ocean acidification may stimulate primary production through increased availability of inorganic carbon in the photic zone, which may in turn change the biogenic flux of dissolved organic carbon (DOC) and the growth potential of heterotrophic bacteria. To investigate the effects of ocean acidification on marine bacterial assemblages, a two-by-three factorial mescosom experiment was conducted using surface sea water from the East Greenland Current in Fram Strait. Pyrosequencing of the V1-V2 region of bacterial 16S ribosomal RNA genes was used to investigate differences in the endpoint (Day 9) composition of bacterial assemblages in mineral nutrient-replete mesocosms amended with glucose (0 µm, 5.3 µm and 15.9 µm) under ambient (250 µatm) or acidified (400 µatm) partial pressures of CO2 (pCO2). All mesocosms showed low richness and diversity by Chao1 estimator and Shannon index, respectively, with general dominance by Gammaproteobacteria and Flavobacteria. Nonmetric multidimensional scaling analysis and two-way analysis of variance of the Jaccard dissimilarity matrix (97% similarity cut-off) demonstrated that the significant community shift between 0 µm and 15.9 µm glucose addition at 250 µatm pCO2 was eliminated at 400 µatm pCO2. These results suggest that the response potential of marine bacteria to DOC input may be altered under acidified conditions.

海洋酸化（Ocean acidification）可通过提升透光层（photic zone）内无机碳的可利用性来刺激初级生产（primary production），进而可能改变溶解有机碳（dissolved organic carbon, DOC）的生物成因通量以及异养细菌（heterotrophic bacteria）的生长潜力。为探究海洋酸化对海洋细菌群落的影响，本研究采用弗拉姆海峡（Fram Strait）东格陵兰洋流（East Greenland Current）区域的表层海水开展了二因素三水平围隔（mesocosm）实验。通过对细菌16S核糖体RNA基因（16S ribosomal RNA genes）的V1-V2可变区进行焦磷酸测序（pyrosequencing），本研究旨在探究在环境二氧化碳分压（ambient pCO2, 250 µatm）与酸化二氧化碳分压（acidified pCO2, 400 µatm）条件下，添加不同浓度葡萄糖（0 µm、5.3 µm、15.9 µm）的矿物质营养充足围隔体系中，实验终点（第9天）的细菌群落组成差异。所有围隔体系的Chao1指数（Chao1 estimator）与香农指数（Shannon index）均显示出较低的物种丰富度与多样性，群落整体以γ-变形菌纲（Gammaproteobacteria）与黄杆菌纲（Flavobacteria）为优势类群。基于97%相似度阈值（97% similarity cut-off）构建的雅卡尔距离矩阵（Jaccard dissimilarity matrix）的非度量多维尺度分析（Nonmetric multidimensional scaling analysis）与双因素方差分析（two-way analysis of variance）结果显示：在250 µatm pCO2条件下，0 µm与15.9 µm葡萄糖添加组间存在的显著群落结构偏移，在400 µatm pCO2条件下被消除。上述结果表明，在酸化海洋环境中，海洋细菌对溶解有机碳输入的响应潜力可能发生改变。