Collaborative Research: CO2 control of oceanic nitrogen fixation and carbon flow through diazotrophs

合作研究：通过固氮生物控制海洋固氮和碳流的二氧化碳

• 批准号: 0722337
• 负责人: David Hutchins
• 金额: $ 59.43万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-05-01 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0722337&HistoricalAwards=false
• 关键词: Collaborative; Research; CO2; control; oceanic

The importance of marine N2 fixation to present ocean productivity and global nutrient and carbon biogeochemistry is now universally recognized. Marine N2 fixation rates and oceanic N inventories are also thought to have varied over geological time due to climate variability and change. However, almost nothing is known about the responses of dominant N2 fixers in the ocean such as Trichodesmium and unicellular N2 fixing cyanobacteria to past, present and future global atmospheric CO2 regimes. Our preliminary data demonstrate that N2 and CO2 fixation rates, growth rates, and elemental ratios of Atlantic and Pacific Trichodesmium isolates are controlled by the ambient CO2 concentration at which they are grown. At projected year 2100 pCO2 (750 ppm), N2 fixation rates of both strains increased 35-100%, with simultaneous increases in C fixation rates and cellular N:P and C:P ratios. Surprisingly, these increases in N2 and C fixation due to elevated CO2 were of similar relative magnitude regardless of the growth temperature or P availability. Thus, the influence of CO2 appears to be independent of other common growth-limiting factors. Equally important, Trichodesmium growth and N2 fixation were completely halted at low pCO2 levels (150 ppm), suggesting that diazotrophy by this genus may have been marginal at best at last glacial maximum pCO2 levels of ~190 ppm. Genetic evidence indicates that Trichodesmium diazotrophy is subject to CO2 control because this cyanobacterium lacks high-affinity dissolved inorganic carbon transport capabilities. These findings may force a re-evaluation of the hypothesized role of past marine N2 fixation in glacial/interglacial climate changes, as well as consideration of the potential for increased ocean diazotrophy and altered nutrient and carbon cycling in the future high-CO2 ocean. We propose an interdisciplinary project to examine the relationship between ocean N2 fixing cyanobacteria and changing pCO2. A combined field and laboratory approach will incorporate in situ measurements with experimental manipulations using natural and cultured populations of Trichodesmium and unicellular N2 fixers over range of pCO2 spanning glacial era to future concentrations (150-1500 ppm). We will also examine how effects of pCO2 on N2 and C fixation and elemental stoichiometry are moderated by the availability of other potentially growth-limiting variables such as Fe, P, temperature, and light. We plan to obtain a detailed picture of the full range of responses of important oceanic diazotrophs to changing pCO2, including growth rates, N2 and CO2 fixation, cellular elemental ratios, fixed N release, photosynthetic physiology, and expression of key genes involved in carbon and nitrogen acquisition at both the transcript and protein level.Broader ImpactsThis project will provide educational opportunities for graduate and undergraduate students with all three PIs and for a postdoctoral scholar. Undergraduate and K-12 education will be furthered through involvement in REU mentoring, high school senior thesis research projects, and classroom curriculum development. Public outreach is planned in the form of a series of public lectures on ocean global change issues. This research has the potential to evolutionize our understanding of controls on N2 fixation in the ocean. Many of our current ideas about the interactions between oceanic N2 fixation, atmospheric CO2, nutrient biogeochemistry, ocean productivity, and global climate change may need revision to take into account previously unrecognized feedback mechanisms between atmospheric composition and diazotrophs. Our findings could thus have major implications for human society, and its increasing dependence on ocean resources in an uncertain future. This project will take the first vital steps towards understanding how a biogeochemically-critical process, the fixation of N2 in the ocean, may respond to our rapidly changing world during the century to come.

现在，普遍认可了海洋N2固定在呈现海洋生产力以及全球营养和生物地球化学的重要性。海洋N2固定率和海洋N库存也被认为由于气候变化和变化而在地质时间内有所不同。但是，几乎一无所知，关于海洋中主要的N2固定器的反应，例如毛状体和单细胞N2固定蓝细菌对过去，现在和未来的全球大气二氧化碳制度。我们的初步数据表明，N2和CO2固定速率，大西洋和太平洋trichodesmium分离株的元素比率受其种植的环境二氧化碳浓度控制。在预计2100 PCO2（750 ppm）的预计年，两种菌株的N2固定速率增加了35-100％，C固定速率同时增加了C固定率和细胞N：P和C：P比率。 令人惊讶的是，由于二氧化碳升高而导致的N2和C固定中的这些增加相对幅度相似，无论生长温度或P的可用性如何。因此，二氧化碳的影响似乎与其他常见的限制因素无关。 同样重要的是，在低PCO2水平（150 ppm）的情况下，毛d虫生长和N2固定完全停止，这表明该属的重18zotrophophophy可能在最终冰川最大PCO2水平上可能是边缘性的，最大PCO2水平约为190 ppm。遗传证据表明，毛状直径的毛氮受到二氧化碳的控制，因为这种蓝细菌缺乏高亲和力的无机碳转运能力。这些发现可能会迫使对过去海洋N2固定在冰川/冰川间气候变化中的假设作用的重新评估，并考虑增加海洋重氮哲学增加的潜力，并改变了未来高CO2海洋中的养分和碳循环。 我们提出了一个跨学科项目，以检查海洋N2固定蓝细菌与改变PCO2之间的关系。合并的野外和实验室方法将使用毛trichodesmium和单细胞N2固定器的自然和培养物种群的实验操作纳入原位测量，以跨越冰川时代到未来的浓度（150-1500 ppm）。我们还将研究PCO2对N2和C固定和元素化学计量的影响如何通过其他潜在的限制变量（例如Fe，P，P，温度和光）的可用性来调节。我们计划获取重要的海洋重氮量对变化PCO2的全部响应的详细图片，包括增长率，N2和CO2固定，细胞元素比率，固定n释放，光合作用生理学，光合作用生理学以及与碳和氮气相关的关键基因的表达以及在转录和蛋白质级别上均可促进的培训。并为博士后学者。本科和K-12教育将通过参与REU指导，高中高中研究项目和课堂课程发展而进一步进一步。公众推广计划以一系列有关海洋全球变化问题的公开演讲的形式。 这项研究有可能进化我们对海洋中N2固定的控制的理解。我们目前关于海洋N2固定，大气二氧化碳，营养生物地球化学，海洋生产力和全球气候变化之间相互作用的想法可能需要修订，以考虑到以前未认识到的大气组成和无重裂嗜酸群之间未认识到的反馈机制。因此，我们的发现可能会对人类社会产生重大影响，以及它在不确定的未来中对海洋资源的日益依赖。该项目将采取第一个至关重要的步骤来理解生物地球化学关键的过程，即N2在海洋中的固定，可能会对我们在未来的世纪中迅速变化的世界做出反应。