In Korean coastal waters (KCW), nutrient loading from the four major rivers usually peaks in summer, probably due to the large amount of water discharge in rainy seasons, but little is known about the responses of the bacterial community composition to inorganic nutrient loading. To gain deeper understanding of variations in marine microbial biodiversity and function with inorganic nutrient loading, a large‐scale mesocosm (1,000 L) experiment was conducted in southern KCW for 10 days in summer (July 27 through August 6, 2015) and the bacterioplankton community composition (BCC) was investigated using 16S rRNA amplicon pyrosequencing method. The bioassays established in the mesocosm were designed with the following each nutrient dosing treatments: nitrate (+N), phosphate (+P), and nitrate plus phosphate (+NP). Among the three treatments, the +NP and +N treatments exhibited the largest and second‐largest increases in phytoplankton abundance, respectively, whereas there was relatively less variation under the +P treatment. Enhanced growth of phytoplankton not only induced increases in pH and bacterial abundance (p < .05) but also led to changes in the BCC: the orders Flavobacteria, Micrococcales, Oceanospirillales, and Rhodobacterales exhibited increases in relative abundance, whereas Methylophilales, Puniceicoccales, SAR11, SAR116, and SAR86 showed a decreasing trend. Inorganic nutrients may directly contribute to variation in the BCC, as the relative abundance of Sphingobacteriales, containing members that undergo chemotaxis toward inorganic nutrients, was increased by the +N treatment. Given that these findings, changes in phytoplankton abundance due to nutrient addition may be the most crucial component resulting in variation in the BCC.

中文翻译：

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韩国南部沿海水域浮游细菌组成对无机养分负荷和浮游植物的响应：中观研究

在韩国沿海水域（KCW）中，四大主要河流的养分负荷通常在夏季达到高峰，这可能是由于雨季大量排水造成的，但是对于细菌群落组成对无机养分负荷的反应知之甚少。为了更深入地了解海洋微生物多样性和无机养分含量变化的功能，夏季（2015年7月27日至2015年8月6日）在KCW南部进行了为期10天的大规模中观试验（1,000 L）和浮游细菌群落使用16S rRNA扩增子焦磷酸测序方法研究了其组成（BCC）。在中膜的生物测定中，设计了以下每种养分定量处理：硝酸盐（+ N），磷酸盐（+ P）和硝酸盐加磷酸盐（+ NP）。在这三种治疗方法中，+ NP和+ N处理的浮游植物丰度增加分别最大和第二大，而+ P处理的变化相对较小。浮游植物的生长增强不仅导致pH值增加和细菌丰度增加（p  <.05），但也导致了BCC的变化：黄杆菌，微球菌，大洋螺菌和红细菌菌的阶数显示相对丰度增加，而嗜甲基菌，杜仲菌，SAR11，SAR116和SAR86呈下降趋势。无机营养物可能直接导致BCC的变化，因为+ N处理增加了包含对无机营养物具有趋化性的成员的Sphingobacteriales的相对丰度。鉴于这些发现，由于添加营养素导致浮游植物丰度的变化可能是导致BCC变化的最关键因素。