Gross nitrogen fixation in the oligotrophic North Pacific Ocean

就像植物将二氧化碳转化为生物质以供生长一样，一些微生物可以将大气中的氮气转化为生物质。这个过程被称为固氮，它在生态学上很重要，因为它允许微生物生活在它们本来无法生长的栖息地。固氮作用在陆地和海洋中都存在。当今海洋学家面临的关键问题之一是解决表层海洋中有多少固氮作用，以及它在时间上、从天到季节的时间尺度上以及在不同生物群的空间上是如何变化的。这项工作将开发海上固氮的高通量分析，以便可以在海洋调查船上进行实时测量。这将有助于改进对水柱的有针对性的采样，并便于将固氮与光合作用速率进行比较，目前光合作用的时间尺度为几分钟到几小时。这项工作将在微生物海洋学研究和教育中心(C-MORE)进行，在那里，主修海洋或地球科学领域的夏威夷原住民和太平洋岛民有机会接受科学培训和获得实验室经验。为了让高中生参与这项工作，并让他们了解科学职业的机会，我们将在当地公立特许学校每年举办一到两次针对六到八年级女孩的外展活动。这项研究将使用一种高灵敏度的还原气体分析仪来量化氢气的产生，氢气是固氮过程中代谢的副产品。为了提高检测下限，海水样品将用惰性气体Ar喷雾，以抑制固氮酶对氮气的还原。在这种情况下，固氮酶将用于还原氮气的所有电子转移到氢气的生产中。这种通过固氮放大氢气生产的技术是生物氢研究界所熟悉的，将被开发用于远洋海洋学目的。这项提议将在实验室培养的重氮菌上测试该方法，以验证氢气产生与传统固氮分析方法(如在生物体内掺入稳定同位素)的比率。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Just as plants convert carbon dioxide into biomass for growth, some microorganisms can convert nitrogen gas from the atmosphere into biomass. This process is called nitrogen fixation and it is important ecologically because it allows microorganisms to live in habitats where they would otherwise be unable to grow. Nitrogen fixation occurs both on land and in the oceans. One of the key questions facing oceanographers today is resolving how much nitrogen fixation is occurring in the surface ocean and how it varies temporally, on timescales of days to seasons, and spatially, across different biomes. This work will develop high throughput analysis of nitrogen fixation at sea so that measurements can be made in real-time onboard oceanographic research vessels. This will help improve targeted sampling of the water-column and facilitate the comparison of nitrogen fixation with rates of photosynthesis which are currently conducted on timescales of minutes to hours. The work will be done at the Center for Microbial Oceanography: Research and Education (C-MORE) where Native Hawaiians and Pacific Islanders majoring in an ocean or earth science-related field are given opportunities for scientific training and laboratory experience. To engage the high-school students in the work and inform them about opportunities in scientific careers, we will hold one to two outreach events per year targeting sixth to eighth grade girls at local public charter schools.This research will use a highly-sensitive reduced gas analyzer to quantify the production of hydrogen gas which is a metabolic by-product of the nitrogen fixation process. To improve the detection limit, seawater samples will be sparged with the inert gas argon to inhibit the reduction of nitrogen gas by the nitrogenase enzyme. Under this scenario, nitrogenase transfers all the electrons used to reduce nitrogen gas into the production of hydrogen. This technique of amplifying the production of hydrogen via nitrogen fixation is familiar to the biohydrogen research community and will be developed for sea-going oceanographic purposes. This proposal will test the method on laboratory cultures of diazotrophs to verify the ratio of hydrogen gas production to traditional methods of nitrogen fixation analysis such as stable isotope incorporation into biomass.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.