Yifan Zhu, Margaret R. Mulholland, Corday R. Selden, Dennis J. McGillicuddy Jr, Josie Mottram, P. Dreux Chappell, Weifeng Gordon Zhang, Julie Granger, Katherine E. Crider, Meredith G. Meyer, Peter W. Bernhardt, Hilde Oliver, Sophie Clayton
{"title":"大西洋中部海湾陆架断裂前沿的氮动态对比:硝酸盐双同位素和硝化基因丰度的启示","authors":"Yifan Zhu, Margaret R. Mulholland, Corday R. Selden, Dennis J. McGillicuddy Jr, Josie Mottram, P. Dreux Chappell, Weifeng Gordon Zhang, Julie Granger, Katherine E. Crider, Meredith G. Meyer, Peter W. Bernhardt, Hilde Oliver, Sophie Clayton","doi":"10.1002/lno.12678","DOIUrl":null,"url":null,"abstract":"<p>Observations and model studies suggest that front dynamics can enhance phytoplankton productivity. This study tested whether frontal systems also increase the abundance of nitrifying microbes and nitrogen recycling during repeat sampling transects across the Mid-Atlantic Bight shelfbreak in July 2019. We measured ammonium concentrations, nitrate dual isotopes (δ<sup>15</sup>N, δ<sup>18</sup>O), and ammonia monooxygenase subunit A (<i>amoA</i>) genes of ammonia-oxidizing archaea (AOA) and bacteria (AOB). In subsurface shelf waters, ammonium concentrations exceeded 2 <i>μ</i>mol L<sup>−1</sup>, due to a temporary imbalance in regeneration from sinking particles and subsequent nitrification. The inverse correlation between nitrate δ<sup>15</sup>N values and ammonium concentrations confirmed nitrate was partially or entirely from local nitrification on the shelf. In contrast, the shelfbreak frontal zone and slope sea subsurface waters had much lower ammonium concentrations (0.1–0.2 <i>μ</i>mol L<sup>−1</sup>) due to tight coupling between ammonium regeneration and nitrification. The deviation of nitrate δ<sup>15</sup>N and δ<sup>18</sup>O from algal uptake-driven 1 : 1 ratio suggests concurrent nitrification in the euphotic zone. The shelfbreak front acted as an ecological boundary where AOA and AOB <i>amoA</i> gene numbers were partitioned, with AOAs abounding in slope waters and AOBs in shelf waters, likely due to ammonium availability. At certain slope stations, deep-water nutrient inputs via isopycnal lifting induced by Gulf Stream intrusions caused unexpectedly high phytoplankton biomass, which doubled nitrifier abundance and potentially stimulated both ammonium regeneration and nitrification. These findings demonstrate distinct distributions of nitrifying microbes along the salinity gradient from shelf to slope and highlight the significant influence of coastal ocean-western boundary current interactions on nitrogen biogeochemistry.</p>","PeriodicalId":18143,"journal":{"name":"Limnology and Oceanography","volume":null,"pages":null},"PeriodicalIF":3.8000,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/lno.12678","citationCount":"0","resultStr":"{\"title\":\"Contrasting nitrogen dynamics across the Mid-Atlantic Bight shelfbreak front: Insights from nitrate dual isotopes and nitrifier gene abundance\",\"authors\":\"Yifan Zhu, Margaret R. Mulholland, Corday R. Selden, Dennis J. McGillicuddy Jr, Josie Mottram, P. Dreux Chappell, Weifeng Gordon Zhang, Julie Granger, Katherine E. Crider, Meredith G. Meyer, Peter W. 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Contrasting nitrogen dynamics across the Mid-Atlantic Bight shelfbreak front: Insights from nitrate dual isotopes and nitrifier gene abundance
Observations and model studies suggest that front dynamics can enhance phytoplankton productivity. This study tested whether frontal systems also increase the abundance of nitrifying microbes and nitrogen recycling during repeat sampling transects across the Mid-Atlantic Bight shelfbreak in July 2019. We measured ammonium concentrations, nitrate dual isotopes (δ15N, δ18O), and ammonia monooxygenase subunit A (amoA) genes of ammonia-oxidizing archaea (AOA) and bacteria (AOB). In subsurface shelf waters, ammonium concentrations exceeded 2 μmol L−1, due to a temporary imbalance in regeneration from sinking particles and subsequent nitrification. The inverse correlation between nitrate δ15N values and ammonium concentrations confirmed nitrate was partially or entirely from local nitrification on the shelf. In contrast, the shelfbreak frontal zone and slope sea subsurface waters had much lower ammonium concentrations (0.1–0.2 μmol L−1) due to tight coupling between ammonium regeneration and nitrification. The deviation of nitrate δ15N and δ18O from algal uptake-driven 1 : 1 ratio suggests concurrent nitrification in the euphotic zone. The shelfbreak front acted as an ecological boundary where AOA and AOB amoA gene numbers were partitioned, with AOAs abounding in slope waters and AOBs in shelf waters, likely due to ammonium availability. At certain slope stations, deep-water nutrient inputs via isopycnal lifting induced by Gulf Stream intrusions caused unexpectedly high phytoplankton biomass, which doubled nitrifier abundance and potentially stimulated both ammonium regeneration and nitrification. These findings demonstrate distinct distributions of nitrifying microbes along the salinity gradient from shelf to slope and highlight the significant influence of coastal ocean-western boundary current interactions on nitrogen biogeochemistry.
期刊介绍:
Limnology and Oceanography (L&O; print ISSN 0024-3590, online ISSN 1939-5590) publishes original articles, including scholarly reviews, about all aspects of limnology and oceanography. The journal''s unifying theme is the understanding of aquatic systems. Submissions are judged on the originality of their data, interpretations, and ideas, and on the degree to which they can be generalized beyond the particular aquatic system examined. Laboratory and modeling studies must demonstrate relevance to field environments; typically this means that they are bolstered by substantial "real-world" data. Few purely theoretical or purely empirical papers are accepted for review.