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

固氮是全球氮循环的重要过程，因为它可以平衡生物有效氮因反硝化作用而损失。然而，关于哪种生物负责固氮以及哪些环境因素控制固氮的争论正在进行中。此外，在Meteor 68/2-3号和Meteor 71/3号巡航期间，对自然浮游生物群落进行了操纵实验，以评估分别控制亚热带北大西洋和地中海浮游植物和固氮生物生长和丰度的因素。在评估固氮作用的重要性方面的一个基本问题是缺乏关于世界海洋中海洋固氮生物的多样性和活动的资料。在Meteor 68/2-3和71/3考察期间，我们收集了固氮率和nifH基因存在和表达分析的样品。使用Taqman探针特异性的最重要的固氮生物的类型存在于我们的样品中，我们建议在这里获得定量信息的丰度和活性的固氮生物的背景下，操作生物测定实验。这项工作将提供关于亚热带北大西洋和地中海的昼夜模式和限制固氮和初级生产的营养物质的基本资料。

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.