Significant N2 fixation by heterotrophs, photoheterotrophs and heterocystous cyanobacteria in two temperate estuaries
Significant N2 fixation by heterotrophs, photoheterotrophs and heterocystous cyanobacteria in two temperate estuaries
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DOI：
10.1038/ismej.2014.119
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发表时间：
2015-02-01
期刊：
影响因子：
11
通讯作者：
Riemann, Lasse
中科院分区：
文献类型：
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作者：
Bentzon-Tilia, Mikkel;Traving, Sachia J.;Riemann, Lasse
氮的固定在许多水生环境中促进浮游植物的生产。然而，在中盐河口和多盐湖河口，由于陆地对氮的高输入，以及假定没有活跃的固氮生物，因此远洋固氮对氮的贡献微乎其微。在这里，我们报告了两个不同的温带河口系统：罗斯基勒峡湾(RF)和大带海峡(GB)，一年来主要重氮营养类群的N-2固定率、nifH基因组成和nifH基因转录本丰度。在这两个地点，浮游N-2的年平均固定率分别为每年17和61 mmolNm(-2)。在RF中，N-2的固定主要伴随着与异养有关的转录本(如假单胞菌sp.)和光异养细菌(例如，A组单细胞重氮蓝藻)。在GB中，两个N-2固定峰中的第一个峰与RF中类似的nifH表达群落相吻合，而第二个峰与一系列重氮菌(包括异养生物以及异质晶体蓝藻鱼腥藻)增加的nifH表达同步。因此，我们首次表明，重要的浮游N-2固定发生在中盐和温带河口，异养、光异养和光合重氮养生物的重要性明显在空间和时间上是不同的。
Nitrogen (N) fixation is fueling planktonic production in a multitude of aquatic environments. In meso-and poly-haline estuaries, however, the contribution of N by pelagic N-2 fixation is believed to be insignificant due to the high input of N from land and the presumed absence of active N-2-fixing organisms. Here we report N-2 fixation rates, nifH gene composition and nifH gene transcript abundance for key diazotrophic groups over 1 year in two contrasting, temperate, estuarine systems: Roskilde Fjord (RF) and the Great Belt (GB) strait. Annual pelagic N-2 fixation rates averaged 17 and 61 mmol Nm(-2) per year at the two sites, respectively. In RF, N-2 fixation was mainly accompanied by transcripts related to heterotrophic (for example, Pseudomonas sp.) and photoheterotrophic bacteria (for example, unicellular diazotrophic cyanobacteria group A). In the GB, the first of two N-2 fixation peaks coincided with a similar nifH-expressing community as in RF, whereas the second peak was synchronous with increased nifH expression by an array of diazotrophs, including heterotrophic organisms as well as the heterocystous cyanobacterium Anabaena. Thus, we show for the first time that significant planktonic N-2 fixation takes place in mesohaline, temperate estuaries and that the importance of heterotrophic, photoheterotrophic and photosynthetic diazotrophs is clearly variable in space and time.