Assessing Microbial Nitrogen Fixation in Ancient Euxinic Basins

评估古代生锈盆地的微生物固氮作用

• 批准号: 0525464
• 负责人: Michael Arthur
• 金额: $ 42.87万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-10-01 至 2009-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0525464&HistoricalAwards=false
• 关键词: Assessing; Microbial; Nitrogen; Fixation; Ancient

EAR-0525464Scientific Basis. Organic nitrogen and bulk nitrogen in ancient black shales is characteristically depleted in 15N. This could indicate that ecosystems fueled by nitrogen fixation were widespread during times of enhanced organic carbon preservation in ocean basins. The association of organic-carbon rich black shales with this isotopic signature for nitrogen fixation poses a paradox: the most productive waters (at least as measured by carbon preservation) in the ancient ocean were possibly starved for fixed nitrogen to fuel normal ocean photosynthesis. Indeed, oxygen depletion in oceanic deep waters would have facilitated microbial removal of nitrogen by denitrification and ammonia oxidation, yet, also favoring the release of phosphate from sediments. We postulate that significant nitrogen fixation is, in fact, to be expected within oxygen-deficient environments with excess dissolved phosphate and low dissolved N/P ratios. We seek to elucidate the relative significance of nitrogen fixation in euxinic (anoxic and sulfidic)environments, particularly at times of near global deep-sea oxygen depletion (so-called "Oceanic Anoxic Events").We propose to ascertain the isotopic signatures and relative contributions of nitrogen derived from cyanobacteria in oxic surface waters and phototrophic sulfur bacteria at or below shallow chemoclines reflected in preserved sedimentary records. We will target isotopic analyses of N and C in biomarkers derived from ancient chlorophyll structures and carotenoid pigment compounds. Isotopic and chemical studies of pigments in modern ecosystems and cultures will form a critical framework and inform our interpretation of ancient signatures. Notably, postdepositional overprints (water-column and sediment diagenesis) can obscure primary nitrogen isotopic signatures in bulk sediment nitrogen and organic nitrogen. Separation and analysis of the nitrogen in geoporphyins provides a powerful way of obtaining primary nitrogen isotope values for biomass produced in ancient euxinic settings.We will analyze sample suites from Lower and middle Cretaceous (Atlantic ODP/DSDP Sites, Italy, Western Interior US), Upper Permian (Japan and China), Upper Devonian (NY) and Proterozoic (AZ) for nitrogen isotope and specific biomarker compounds indicative of important microbial groups. The proposed research will also require sampling and analysis of modern euxinic water columns and sediments (Fayetteville-Green Lake, NY and the Black Sea) and selected culture experiments in order to further constrain the relative nitrogen isotope discrimination between porphyrins and cell biomass for important microbial groups.Broader Impacts. The proposed research will constitute Ph.D. dissertation work for Jamey Fulton and Chris Junium. It will facilitate international opportunities for these students in the laboratory of Dr. Brendan Keely, at the University of York in Great Britain. Two undergraduate summer interns will be co-sponsored by this project and mentored by the PIs. Support will be provided to an existing and successful internship program (currently funded by an IGERT award) that provides students with rich experiences in biogeochemical research at Penn State. This internship program has a strong track record in recruiting minority (27.9%) and female students (76.7%), and it provides scientific, professional and social mentoring for all participants.Eutrophic conditions currently promote seasonal hypoxia or anoxia in coastal regions of the U.S. (e.g., Long Island Sound, Chesapeake Bay, Louisiana shelf) and, in some cases, these conditions are worsening. As a result, the balance between N and P availability to primary producers is being altered, due in part to phosphate liberation from sediments and denitrification accompanying low dissolved oxygen concentrations in the water column (Carpenter and Capone, 1998). Our proposed research on the response of microbial systems to development of anoxia in deep time should bring a greater understanding of such ecosystems, allowing better predictions to be made for future impacts.

耳朵——0525464——科学依据。古黑色页岩有机氮和块状氮在15N时明显衰竭。这可能表明，在有机碳保存增强的时期，以固氮为燃料的生态系统在海洋盆地中广泛存在。富含有机碳的黑色页岩与固氮同位素特征的联系构成了一个悖论：古代海洋中最富生产力的水域（至少从碳保存的角度来看）可能迫切需要固定氮来为正常的海洋光合作用提供燃料。事实上，海洋深水中的氧气消耗会促进微生物通过反硝化和氨氧化去除氮，但也有利于沉积物中磷酸盐的释放。我们假设，事实上，在具有过量溶解磷酸盐和低溶解N/P比的缺氧环境中，可以预期显著的固氮作用。我们试图阐明在缺氧（缺氧和硫化物）环境中固氮的相对意义，特别是在接近全球深海缺氧的时候（所谓的“海洋缺氧事件”）。我们建议确定沉积记录中反映的含氧地表水蓝藻和光养硫细菌的氮同位素特征和相对贡献。我们将针对来自古代叶绿素结构和类胡萝卜素色素化合物的生物标志物进行N和C的同位素分析。对现代生态系统和文化中颜料的同位素和化学研究将形成一个关键的框架，并为我们对古代特征的解释提供信息。值得注意的是，沉积后叠印（水柱和沉积物成岩作用）可以模糊大块沉积物中氮和有机氮的原生氮同位素特征。地卟啉中氮的分离和分析为获得古缺氧环境下生物量的原始氮同位素值提供了一种有力的方法。我们将分析下白垩纪和中白垩纪（大西洋ODP/DSDP遗址，意大利，美国西部内陆），上二叠纪（日本和中国），上泥盆纪（NY）和元古代（AZ）的样品套件，以获取氮同位素和指示重要微生物群的特定生物标志物化合物。拟议的研究还需要对现代富氧水柱和沉积物（纽约州费耶特维尔-格林湖和黑海）进行采样和分析，并选择培养实验，以进一步限制卟啉和重要微生物群细胞生物量之间的相对氮同位素区别。更广泛的影响。拟议的研究将构成杰米富尔顿和克里斯朱尼姆的博士论文工作。它将为这些学生在英国约克大学Brendan Keely博士的实验室提供国际机会。本项目将共同资助两名本科生暑期实习生，并由pi指导。支持现有的和成功的实习计划（目前由IGERT奖资助），为学生提供宾夕法尼亚州立大学生物地球化学研究的丰富经验。该实习项目在招收少数民族学生（27.9%）和女生（76.7%）方面有着良好的记录，并为所有参与者提供科学、专业和社会指导。富营养化条件目前在美国沿海地区（如长岛湾、切萨皮克湾、路易斯安那大陆架）促进季节性缺氧或缺氧，在某些情况下，这些条件正在恶化。因此，初级生产者获得氮和磷的平衡正在改变，部分原因是沉积物中磷酸盐的释放和水柱中溶解氧浓度低的反硝化作用（Carpenter和Capone， 1998）。我们提出的关于微生物系统对深时间缺氧发展的响应的研究应该带来对这种生态系统的更好理解，从而更好地预测未来的影响。