| Zhang Run,Zhang Dongsheng,Chen Min,Jiang Zhibing,Wang Chunsheng,Zheng Minfang,Qiu Yusheng,Huang Jie. 2019. N2 fixation rate and diazotroph community structure in the western tropical North Pacific Ocean. Acta Oceanologica Sinica, 38(12):26－34 |
| N2 fixation rate and diazotroph community structure in the western tropical North Pacific Ocean |
| 热带北太平洋西部固氮速率及固氮微生物组成 |
| Received:December 28, 2018 |
| DOI：10.1007/s13131-019-1513-4 |
| Key words:western tropical North Pacific Ocean (WTNP) N2 fixation 15N isotope tracer assay unicellular diazotroph |
| 中文关键词: 热带北太平洋西部 固氮作用 15N同位素示踪法 单细胞固氮生物 |
| 基金项目:The National Basic Research Program of China under contract No. 2015CB452903; the Foundation of China Ocean Mineral Resources R&D Association under contract No. DY135-E2-2-03; the Science and Technology Basic Resources Investigation Program of China under contract No. 2017FY201403; the National Natural Science Foundation of China under contract Nos 41676174, 41206104 and 41876198. |
| Author Name | Affiliation | E-mail | | Zhang Run | College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China | zhangrun@xmu.edu.cn | | Zhang Dongsheng | Key Laboratory of Marine Ecosystem and Biogeochemistry, State Oceanic Administration/Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China | | | Chen Min | College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China | | | Jiang Zhibing | Key Laboratory of Marine Ecosystem and Biogeochemistry, State Oceanic Administration/Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China | | | Wang Chunsheng | Key Laboratory of Marine Ecosystem and Biogeochemistry, State Oceanic Administration/Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China | wangsio@sio.org.cn | | Zheng Minfang | College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China | | | Qiu Yusheng | College of Ocean and Earth Sciences, Xiamen University, Xiamen 361102, China | | | Huang Jie | Ministry of Education Key Laboratory for Earth System Modeling/Department of Earth System Science, Tsinghua University, Beijing 100084, China | |
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| Abstract: |
| In the present study, we report N2 fixation rate (15N isotope tracer assay) and the diazotroph community structure (using the molecular method) in the western tropical North Pacific Ocean (WTNP) (13°–20°N, 120°–160°E). Our independent evidence on the basis of both in situ N2 fixation activity and diazotroph community structure showed the dominance of unicellular N2 fixation over majority of the WTNP surface waters during the sampling periods. Moreover, a shift in the diazotrophic composition from unicellular cyanobacteria group B-dominated to Trichodesmium spp.-dominated toward the western boundary current (Kuroshio) was also observed in 2013. We hypothesize that nutrient availability may have played a major role in regulating the biogeography of N2 fixation. In surface waters, volumetric N2 fixation rate (calculated by nitrogen) ranged between 0.6 and 2.6 nmol/(L·d) and averaged (1.2±0.5) nmol/(L·d), with < 10 μm size fraction contributed predominantly (88%±6%) to the total rate between 135°E and 160°E. Depth-integrated N2 fixation rate over the upper 200 m ranged between 150 μmol/(m2·d) and 480 μmol/(m2·d) (average (225±105) μmol/(m2·d). N2 fixation can account for 6.2%±3.7% of the depth-integrated primary production, suggesting that N2 fixation is a significant N source sustaining new and export production in the WTNP. The role of N2 fixation in biogeochemical cycling in this climate change-vulnerable region calls for further investigations. |
| 中文摘要: |
| 生物固氮作用是海洋最主要的外源性新氮来源。本研究报道了热带北太平洋西部（13-20°N，120-160°E，WTNP）基于15N稳定同位素示踪法测定固氮速率及基于分子生物学手段所获得固氮生物组成信息。固氮速率的粒级分布及固氮生物组成信息共同证实，在采样时期WTNP得固氮作用主要来自单细胞固氮生物的贡献。在一条东西向断面上的结果表明，固氮生物组成从中心海盆区的单细胞蓝藻（UCYN-B）为主，向西边界流（黑潮区）转变为以束毛藻为主。推测固氮生物组成的空间变化，在很大程度上反映了微量营养盐可获得性的调控。表层水固氮速率变化范围是0.6-2.6 nmol/（L d），平均值为1.2±0.5 nmol/（L d），在135°E-160°E之间，固氮速率的主要贡献份额（88%±6%）来自 <10 μm粒级。深度积分（0-200 m）固氮速率变化范围是150-480 μmol/（m2 d），平均值为225±105 μmol/（m2 d）。进一步地，估算固氮作用可支持初级生产力氮需求的份额是6.2%±3.7%，表明固氮作用是WTNP重要的新氮来源。考虑到WTNP对气候变化相当敏感，有必要对该海区加强研究，以厘清固氮作用在海洋生物地球化学循环中的作用。 |
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