Facets of diazotrophy in the oxygen minimum zone waters off Peru
Facets of diazotrophy in the oxygen minimum zone waters off Peru
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DOI：
10.1038/ismej.2014.71
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发表时间：
2014-05
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通讯作者：
C. Loescher;T. Grosskopf;Falguni Desai;D. Gill;H. Schunck;P. Croot;C. Schlosser;S. Neulinger;N. Pinnow;G. Lavik;M. Kuypers;J. LaRoche;R. Schmitz
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作者：
C. Loescher;T. Grosskopf;Falguni Desai;D. Gill;H. Schunck;P. Croot;C. Schlosser;S. Neulinger;N. Pinnow;G. Lavik;M. Kuypers;J. LaRoche;R. Schmitz
固氮，即生物将氮气(N_2)还原为氨(NH_4+)，从数量上讲是向公海输送新氮(N)的最重要的外部来源。传统上，海洋固氮菌(重氮菌)的生态位被归因于热带少营养表层水域，通常耗尽固定N，以蓝藻为主的重氮营养群落。尽管这适用于大片海洋，但生物地球化学模型和系统发育研究表明，海洋重氮营养生态位可能比以前所认为的要广泛得多，从而对全球氮收支产生重大影响。在这里，我们报道了NifH的组成、分布和丰度，它是N2固定的功能基因标记。我们的结果表明，在秘鲁近海的氧气最小区(OMZ)存在八种重氮菌。尽管蛋白细菌分支在总体上占主导地位，但鉴定出了两个附属于螺旋藻和古生菌的聚类群。在OMZ水体中检测到了N2固定，并受到有机碳源的刺激，支持了非光营养重氮菌正在积极固定NN的观点。N2固定、硝化、厌氧氨氧化和反硝化等关键功能基因的共同存在表明，秘鲁OMZ存在着N输入和N损失过程的密切空间耦合。重氮菌在整个水柱中的广泛分布增加了一种新的观点，即海洋重氮菌的栖息地可以扩大到低氧/高硝酸盐地区。此外，我们的统计分析表明，亚硝酸盐−和PO43−是影响海洋生态系统重氮化分布的主要因素。鉴于全球变暖导致海洋脱氧作用的预期增加，我们的发现表明，OMZ作为固定N2的利基环境的重要性在未来可能会增加。
Nitrogen fixation, the biological reduction of dinitrogen gas (N2) to ammonium (NH4+), is quantitatively the most important external source of new nitrogen (N) to the open ocean. Classically, the ecological niche of oceanic N2fixers (diazotrophs) is ascribed to tropical oligotrophic surface waters, often depleted in fixed N, with a diazotrophic community dominated by cyanobacteria. Although this applies for large areas of the ocean, biogeochemical models and phylogenetic studies suggest that the oceanic diazotrophic niche may be much broader than previously considered, resulting in major implications for the global N-budget. Here, we report on the composition, distribution and abundance ofnifH, the functional gene marker for N2fixation. Our results show the presence of eight clades of diazotrophs in the oxygen minimum zone (OMZ) off Peru. Although proteobacterial clades dominated overall, two clusters affiliated to spirochaeta and archaea were identified. N2fixation was detected within OMZ waters and was stimulated by the addition of organic carbon sources supporting the view that non-phototrophic diazotrophs were actively fixing dinitrogen. The observed co-occurrence of key functional genes for N2fixation, nitrification, anammox and denitrification suggests that a close spatial coupling of N-input and N-loss processes exists in the OMZ off Peru. The wide distribution of diazotrophs throughout the water column adds to the emerging view that the habitat of marine diazotrophs can be extended to low oxygen/high nitrate areas. Furthermore, our statistical analysis suggests that NO2−and PO43−are the major factors affecting diazotrophic distribution throughout the OMZ. In view of the predicted increase in ocean deoxygenation resulting from global warming, our findings indicate that the importance of OMZs as niches for N2fixation may increase in the future.