New Experimental Approaches to the Study of Organic NitrogenCycling in Marine Microplankton

点击翻译按钮获取中文摘要

Knowledge of how the marine nitrogen cycle and the organisms mediating the transformations of nitrogen in the cycle have changed tremendously over the past five years. Bacteria can compete with phytoplankton for inorganic nitrogen, and yet, may also serve as regenerators of nitrogen compounds depending upon their nutritional and physiological state. Changing concepts of how systems work frequently go hand in hand with advances in methodology. This is true for marine nitrogen cycling, in particular, the role of organic nitrogen. The use of 15N- labelled substrates have been the major tool with which inorganic nitrogen uptake and NH4+ regeneration have been studied to date. This research addresses the relationship and couplings between inorganic nitrogen, in the form of NH4+, and organic nitrogen in the form of urea and amino acids, using a number of new techniques, including: 1) a dual labelling techniques for simultaneous measurements of uptake and release of urea: 2) a filtering technique for the bacterial fraction that is compatible with mass spectrometry; 3) ion exchange column techniques for recovering 15N-labelled DON/amino acids from incubation experiments; and 4) measurement of low-level NH4+ concentrations by solvent extraction. The combination of laboratory and field experiments are aimed at establishing relationships between organism size and nutritional state, and microplankton NH4+ and urea regeneration.