Study of the factors controlling nitrogen fixation in the Subtropical North Atlantic and in the Mediterranean: Experimental manipulation of natural microbial populations on board of Meteor 68/3 and 71/3 expeditions

固氮是全球氮循环中的一个重要过程，因为它可以平衡通过反硝化作用损失的生物有效氮。然而，关于哪些生物体负责，以及哪些环境因素控制着固氮，一直存在着争论。此外，在Meteor 68/2-3和Meteor 71/3航次期间进行了自然浮游生物群落的操纵性实验，以评估分别控制北大西洋亚热带和地中海浮游植物和固氮菌生长和丰度的因素。评估固氮重要性的一个基本问题是缺乏关于世界海洋中海洋重氮菌多样性和活性的信息。在流星68/2-3和71/3探险期间，我们收集了固氮率和nifH基因存在和表达的样本。使用Taqman探针针对我们样品中存在的最重要的重氮菌种型，我们建议在操纵性生物测定实验的背景下获得重氮菌丰度和活性的定量信息。这项工作将提供有关亚热带北大西洋和地中海固氮和初级生产的日变化模式和营养物质的基本信息。

Nitrogen fixation is an important process for the global nitrogen cycle because it can balance the biologically available nitrogen lost through denitrification. However, there is ongoing debate concerning which organisms are responsible for, and what environmental factors, control nitrogen fixation. Additionally, Manipulative experiments of natural plankton communities have been conducted during the Meteor 68/2-3 and Meteor 71/3 cruises in order to assess the factors controlling phytoplankton and diazotroph growth and abundance in the Subtropical North Atlantic and the Mediterranean Sea, respectively. One of the fundamental questions in assessing the importance of nitrogen fixation is the paucity of information concerning the diversity and activity of marine diazotrophs in the world's ocean. During the Meteor 68/2-3 and 71/3 expeditions, we collected samples for nitrogen fixation rates and for the analysis ofnifH gene presence and expression. Using Taqman probes specific for the most important diazotroph phylotypes present in our samples, we propose here to obtain quantitative information for the abundance and activity of diazotrophs in the context of manipulative bioassay experiments. This work will provide basic information concerning the diel patterns of and the nutrients limiting nitrogen fixation and primary production in the Subtropical North Atlantic and the Mediterranean.