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

Carpenter 9317738这个项目继续研究毛霉和其他浮游性氮气固定物的生态、生理和生化，在热带北大西洋、加勒比海西部、澳大利亚东北部和西北部比以前更广泛的地区进行了几次巡航。一个目标是评估毛霉菌种群丰度和氮气固定，同时评估浮游植物种群丰度和N同化、新的和再生的氮。将使用超微结构和nifH基因测序进行物种区分。这将涉及蛋白质标记、超微结构研究和分子生物学方法。下一个目标是确定固氮酶活性的昼夜周期性现象是否是这些种群的共同特征，以及进一步研究这种周期性的基础和O2保护机制。该项目将继续研究毛霉菌C和N的去向，确定不稳定有机物(谷氨酸和其他氨基酸)的释放率以及甲壳类桡足类动物的捕食率。关于放牧，该项目将评估毒素的存在的重要性，这些毒素作为毛霉菌种类的一种而抑制放牧。此外，该项目将研究毛霉菌浮力逆转的机制，以及关于适应意义的实地研究，以及使用同位素和生物化学“生物标记物”来跟踪毛霉菌生物量的命运。最后，毛霉菌种群测量将与生物光学测量相结合，目的是开发遥感算法。总体而言，该项目将提供信息，以批判性地评估毛霉菌是新氮的重要数量输入的推断。这一信息将有助于全面了解浮游氮气固定物的生态、生理和生物化学，以及它们在海洋碳和氮通量中的作用。***

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. ***