Assessing the diversity and activity of diazotrophs in the tropical and Subtropical Atlantic

直到最近，固氮在海洋氮循环中的重要性可能还被低估了。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的信息。这个问题是通过研究从流星55期间收集的过滤海水样本中提取的DNA中nifH基因的序列多样性来解决的。通过对平行样品中提取的RNA进行逆转录和聚合酶链式反应(RT-PCR)分析，将证实来自不同种类的重氮菌的nifH基因确实在原位表达。样本也取自7个营养添加生物测定试验中的4个，这些试验旨在从实验上解决初级生产力和固氮的营养限制问题。我们将研究来自不同生物化验方法的样本中nifH基因的存在和表达情况，以评估添加某些营养物质是否有利于浮游生物群落中的重氮菌的生长。结果将在生物化验结果和巡航期间收集的与固氮和大气粉尘沉积相关的其他测量的背景下进行分析。

The importance of nitrogen fixation in the marine nitrogen cycle has probably been underestimated until recently. One of the fundamental questions in assessing the importance of nitrogen fixation is the paucity of information concerning the diversity of marine diazotrophs in the world's ocean. This question is being addressed here by looking at the sequence diversity of nifH genes in DNA extracted from filtered seawater samples collected during Meteor 55. Confirmation that the nifH genes from diverse clades of diazotrophs are indeed expressed in situ will be seeked via reverse transcription and polymerase chain reaction (RT-PCR) analysis of RNA extracted from parallel samples. Samples were also taken from 4 of 7 nutrient addition bioassay experiments designed to address experimentally the question of nutrient limitation of primary productivity and nitrogen fixation. The presence and expression of the nifH genes will be studied in the samples from the different bioassays, in order to assess whether or not the addition of certain nutrients favoured the growth of diazotrophs within the plankton community. The results will be analyzed in the context of the bioassay results and other measurements collected during the cruise that are relevant to nitrogen fixation and atmospheric dust deposition.