Comparative assessment of nitrogen fixation rate by ^(15)N_(2) tracer assays in the South China Sea  

作　　者：Danyang Li Minfang Zheng Yusheng Qiu Limin Lai Nengwang Chen Hongmei Jing Run Zhang Min Chen 

机构地区：[1]College of Ocean and Earth Sciences,Xiamen University,Xiamen,361102,China [2]Fisheries College,Jimei University,Xiamen,361021,China [3]College of the Environment and Ecology,Xiamen University,Xiamen,361102,China [4]State Key Laboratory of Marine Environment Science,Xiamen University,Xiamen,361102,China [5]Key Laboratory for Experimental Study under Deep-sea Extreme Conditions,Institutes of Deep-sea Science and Engineering,Chinese Academy of Sciences,Sanya,572000,China

出　　处：《Acta Oceanologica Sinica》2023年第1期75-82,共8页海洋学报（英文版）

基　　金：The National Natural Science Foundation of China under contract Nos 42076042 and 41721005;the Fund of Ministry of Science and Technology of China under contract No.2017FY201403;the Fund of China Ocean Mineral Resources R&D Association under contract No.DY135-13-E2-03.

摘　　要：Nitrogen fixation is one of the most important sources of new nitrogen in the ocean and thus profoundly affects the nitrogen and carbon biogeochemical processes.The distribution,controlling factors,and flux of N2 fixation in the global ocean remain uncertain,partly because of the lack of methodological uniformity.The^(15)N_(2)tracer assay(the original bubble method→the^(15)N_(2)-enriched seawater method→the modified bubble method)is the mainstream method for field measurements of N2 fixation rates(NFRs),among which the original bubble method is the most frequently used.However,accumulating evidence has suggested an underestimation of NFRs when using this method.To improve the availability of previous data,we compared NFRs measured by three^(15)N_(2)tracer assays in the South China Sea.Our results indicate that the relationship between NFRs measured by the original bubble method and the^(15)N_(2)-enriched seawater method varies obviously with area and season,which may be influenced by incubation time,diazotrophic composition,and environmental factors.In comparison,the relationship between NFRs measured by the original bubble method and the modified bubble method is more stable,indicating that the N2 fixation rates based on the original bubble methods may be underestimated by approximately 50%.Based on this result,we revised the flux of N2 fixation in the South China Sea to 40 mmol/(m2·a).Our results improve the availability and comparability of literature NFR data in the South China Sea.The comparison of the^(15)N_(2)tracer assay for NFRs measurements on a larger scale is urgently necessary over the global ocean for a more robust understanding of the role of N2 fixation in the marine nitrogen cycle.

关 键 词：N2 fixation rate South China Sea ^(15)N_(2)tracer assay 

分 类 号：P736.4[天文地球—海洋地质]