Exploratory research on new source of atmospheric reactive nitrogen focusing on marine nitrogen-fixing organisms

2022 Fiscal Year Final Research Report

• Project/Area Number: 21K19835
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 63:Environmental analyses and evaluation and related fields
• Research Institution: Hokkaido University
• Principal Investigator: Miyazaki Yuzo 北海道大学, 低温科学研究所, 助教 (60376655)
• Co-Investigator(Kenkyū-buntansha): 鈴木 光次 北海道大学, 地球環境科学研究院, 教授 (40283452)
• Project Period (FY): 2021-07-09 – 2023-03-31
• Keywords: 大気反応性窒素 / 海洋窒素固定 / アンモニア / 有機態窒素 / 海洋大気

Outline of Final Research Achievements

This study aimed to elucidate the contribution of marine nitrogen-fixing microorganism (Trichodesmium) to the formation of atmospheric reactive nitrogen by a laboratory incubation experiment. During the incubation period of approximately two months, it was observed that dissolved nitrogen was exuded from Trichodesmium during the exponential phase of the growth stage. Throughout the experiment, ammonium/ammonia and water-soluble organic nitrogen (WSON) were the major reactive nitrogen components in both particulate and gas phases. Overall results showed that the atmospheric emission of acidic WSON was more evident during the exponential and stationary growth phases, while the emissions of basic reactive nitrogen were more significant during the decline and death phases. This study demonstrated the sea-to-air emissions of ammonia and WSON associated with the growth and decline of nitrogen-fixing microorganism for the first time.

Free Research Field

大気化学

Academic Significance and Societal Importance of the Research Achievements

海洋の窒素固定生物は、従来考えられてきた熱帯・亜熱帯などの貧栄養海域以外でも近年、極域などより広範囲にその存在が報告されている。海洋生物にとっての「利用源」である、窒素固定で生成された反応性窒素が大気の「放出源」になるという発想は従来なく、本研究は大気－海洋間の窒素収支の定量的理解において重要な知見をもたらし、その学術的意義は大きい。本研究で明らかになった海水から大気へ移行する反応性窒素は、大気微粒子の酸性度や新粒子生成など、大気質や粒子数変化の理解において重要であり、雲の生成などを通して海洋微生物が及ぼす気候影響などの理解において新たな研究展開が期待できる。