Table_3_Drivers of Regional Bacterial Community Structure and Diversity in the Northwest Atlantic Ocean.xlsx

The fundamental role of bacteria in global biogeochemical cycles warrants a thorough understanding of the factors controlling bacterial community structure. In this study, the integrated effect of seasonal differences and spatial distribution on bacterial community structure and diversity were investigated at the regional scale. We conducted a comprehensive bacterial survey, with 451 samples of the Scotian Shelf sector of the Northwest Atlantic Ocean during spring and fall of 2014 and 2016, to analyze the effects of physicochemical gradients on bacterial community structure. Throughout the region, Pelagibacteraceae and Rhodobacteraceae were the most common in the free-living fraction, while Flavobacteriia and Deltaproteobacteria were more abundant in the particle-associated fraction. Overall, there was strong covariation of the microbial community diversity from the two size fractions. This relationship existed despite the statistically significant difference in community structure between the free-living and particle-associated size fractions. In both size fractions, distribution patterns of bacterial taxa, and species within taxa, displayed temporal and spatial preferences. Distinct bacterial assemblages specific to season and depth in the water column were identified. These distinct assemblages, consistent for both 2014 and 2016, suggested replicable patterns in microbial communities for spring and fall in this region. Over all sites, temperature and oxygen values were highly correlated with community similarity, and salinity and oxygen values were the most strongly positively- and negatively correlated with alpha diversity, respectively. However, the strengths of these correlations depended on the depth and season sampled. The bathymetry of the Scotian Shelf, the abrupt shelf break to the Scotian Slope and the major ocean currents dominating in the region led to the formation of distinct on-shelf and off-shelf bacterial communities both in spring and fall. The highest species richness was observed at the shelf break, where water masses from the two major currents meet. Our study establishes the baseline for assessing future changes in the bacterial community of the Scotian Shelf waters, a rapidly changing sector of the Atlantic Ocean.

细菌在全球生物地球化学循环中的核心作用，亟需我们深入解析调控细菌群落结构的各类影响因素。本研究以区域尺度为研究范围，探究了季节差异与空间分布对细菌群落结构及多样性的综合调控效应。我们于2014年与2016年的春、秋两季，对西北大西洋斯科舍陆架（Scotian Shelf）海域采集了共计451份样本，开展全面的细菌群落调查，以解析物理化学梯度对细菌群落结构的影响。在该研究区域内，远洋杆菌科（Pelagibacteraceae）与红杆菌科（Rhodobacteraceae）为游离态组分（free-living fraction）中的优势类群；而黄杆菌纲（Flavobacteriia）与δ-变形菌纲（Deltaproteobacteria）则在颗粒结合态组分（particle-associated fraction）中更为富集。整体而言，两种粒径组分的微生物群落多样性呈现显著的共变关系；尽管游离态与颗粒结合态组分的群落结构存在统计学意义上的显著差异，但二者仍保持这一相关关系。在两类粒径组分中，细菌类群及其内部物种的分布模式均表现出明显的时空偏好性。研究鉴定出了与季节及水体深度特异性相关的独特细菌群落组合；2014年与2016年的观测结果均一致呈现这类特征，表明该区域春、秋两季的微生物群落分布模式具备可重复性。在所有采样站位中，水温与溶解氧浓度与群落相似性呈高度相关；盐度与溶解氧分别是与α多样性（alpha diversity）呈最强正相关与最强负相关的环境因子。不过上述相关关系的强度会随采样深度与季节发生变化。斯科舍陆架的海底地形、与斯科舍斜坡（Scotian Slope）之间存在的陡峭陆架坡折（shelf break），以及区域内主导的主要洋流，共同促成了春、秋两季陆架区与外陆架区形成截然不同的细菌群落结构。在两股主要洋流交汇的陆架坡折区域，物种丰富度达到最高水平。本研究为评估大西洋快速变化的海域——斯科舍陆架海域的细菌群落未来变化提供了基准基线。