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

在过去的五年中，关于海洋氮循环和在循环中调节氮转化的生物的知识发生了巨大的变化。细菌可以与浮游植物竞争无机氮，但也可以根据其营养和生理状态作为氮化合物的再生器。改变系统如何工作的概念经常与方法论的进步密切相关。这对海洋氮循环来说是正确的，特别是有机氮的作用。15N标记基质的使用是迄今为止研究无机氮吸收和NH4+再生的主要工具。本研究利用一系列新技术探讨了NH4+形式的无机氮与尿素和氨基酸形式的有机氮之间的关系和耦合，包括：1)用于同时测量尿素吸收和释放的双重标记技术；2)与质谱相容的细菌部分过滤技术；3)从培养实验中回收15n标记DON/氨基酸的离子交换柱技术；4)溶剂萃取法测定低浓度NH4+浓度。通过室内和野外试验相结合的方法，旨在建立生物大小与营养状态、浮游微生物NH4+与尿素再生之间的关系。

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.