Collaborative Research: Physiology, Ecology, and Biochemistry of Nitrogen Fixation by Marine Planktonic Microorganisms (ABR)

该项目继续研究毛霉菌和其他浮游固氮生物的生态学、生理学和生物化学，并在北大西洋热带、加勒比海西部、澳大利亚东北部和西北部进行了几次巡航，比以往的工作更广泛。目的之一是评估木霉种群丰度和固氮，同时评估浮游植物种群丰度和N同化、新氮和再生氮。物种区分将通过超微结构和nifH基因测序来完成。这将涉及蛋白质标记和超微结构研究以及分子生物学方法。下一个目标是确定氮酶活性的昼夜周期性现象是否是这些种群的共同特征，并进一步研究这种周期性的基础和氧气保护的机制。该项目将继续研究C和N Trichodesmium的命运，确定不稳定有机物（谷氨酸和其他氨基酸）的释放率以及harpacytacoid桡足类动物的掠食率。关于放牧，该项目将评估毒素存在的重要性，这些毒素抑制了木霉属植物的放牧。此外，该项目将研究木霉浮力逆转的机制，以及对适应意义的实地研究，并使用同位素和生化“生物标志物”来跟踪木霉生物量的命运。最后，木霉种群测量将与生物光学测量相结合，目标是开发遥感算法。总的来说，该项目将提供信息，以批判性地评估Trichodesmium是新N的重要数量输入的推论。这一信息将大大有助于全面了解浮游固氮生物的生态学、生理学和生物化学及其在海洋中C和N通量中的作用。＊＊＊

Carpenter 9317738 This project continues studies into the ecology, physiology and biochemistry of Trichodesmium and other planktonic N2 fixers, undertaking several cruises in more widespread areas of tropical North Atlantic, W Caribbean, NE & NW Australia than pervious efforts. One objective is to assess Trichodesmium population abundance and N2 fixation along with concurrent assessment of phytoplankton population abundance and N assimilation, new and regenerated nitrogen. Species distinctions will be done using ultrastructure and nifH gene sequencing. This will involve protein labeling and ultrastructural studies and molecular biological approaches. The next objective is to determine whether the phenomenon of diel periodicity in nitrogenase activity is a common characteristic of these populations as well as further examining the basis for this periodicity and the mechanisms of O2 protection. The project will continue to examine the fate of Trichodesmium C and N, determine the release rates of labile organics (glutamate and other amino acids) and the grazing rates by harpacytacoid copepods. With respect to grazing, the project will to assess the importance of the presence of toxins, which inhibit grazing as a function of the species of Trichodesmium. In addition, the project will examine the mechanisms of Trichodesmium buoyancy reversals, along with field research on adaptational significance, and the use of isotopic and biochemical "biomarkers" for tracking the fate of Trichodesmium biomass. Finally, Trichodesmium population measurements will be coupled with biooptic measurements with the goal of developing remote sensing algorithms. Overall, the project will provide information to assess critically the inference that Trichodesmium is a quantitatively significant input of new N. This informantion will contribute substantively towards obtaining a complete understanding of the ecology, physiology and biochemistry of planktonic N2 fixers and their role in C and N fluxes in the oceans. ***