Collaborative Research: Assessing the Genetic Potential andPhysiological Controls of N2 Fixation in a N-Limited Estuary

9615772尽管大气中存在大量的气态氮气，但河口的生产力往往受氮(N)有效性的控制。氮气固定，即将大气中的氮气转化为细胞氮，可以在淡水生态系统的浮游生物中以很高的速度发生，这是由于固定氮气的蓝藻密集繁殖。这些水华可能是有毒的，并导致水味和气味问题。这样的水华在海洋系统中很少见，即使是正在经历富营养化(由于营养投入增加而变得更有生产力)的系统也是如此。淡水中固定氮气生物的优势与河口和海洋中明显缺乏固定氮气生物之间的对比，为拟议的研究提供了基础。河口定义了从淡水到海洋环境的过渡，从而为研究控制淡水和海洋环境中氮气固定水华的因素提供了基础。这项研究的目的是确定氮固定生物在纽兹河河口淡水、中盐和真盐河段的空间和时间分布。这一研究项目中建立的概念框架将为理解海洋、河口和淡水环境中的固氮潜力提供一个新的视角，这将有助于理解固氮水华可能在何时何地发生，以响应养殖富营养化的威胁。这项研究的一个特别新颖的方面是，将使用分子生物学方法，通过实验操作来确定盐度和营养物质如何影响特定的氮固定种群的分布、生长和活性。这些实验的结果将为调节河口、淡水和海洋环境中的生产力和藻类水华形成提供新的信息。

9615772 Paerl Productivity in estuaries is often controlled by nitrogen(N) availability,even though there is a vast reservoir of gaseous N2 in the atmosphere. N2 fixation, the conversion of atmospheric N2 into cellular nitrogen, can occur at high rates in the plankton of freshwater ecosystems, due to dense blooms of N2 fixing cyanobacteria. These blooms can be toxic and cause water taste and odor problems. Such blooms are scarce in marine systems, even those undergoing eutrophication (becoming more productive as a result of increased nutrient inputs). The contrast between the predominance of N2 fixing organisms in freshwater and the apparent dearth of N2 fixing organisms in estuaries and oceans, provides the basis for the proposed research. Estuaries define the transition from freshwater to the marine environment, and thus provide a basis for investigating the factors that control N2 fixing blooms in both freshwater and marine environments. This objective of this research is to define how N2 fixing organisms are distributed spatially and temporally in the freshwater, mesohaline and euhaline reaches of the Neuse River estuary. The conceptual framework developed in this research project will provide a new perspective for understanding N2 fixation potentials in marine, estuarine and freshwater environments, which will help to understand when and where nitrogen-fixing blooms are likely to occur in response to the threat of cultural eutrophication. A particularly novel aspect of this investigation is that experimental manipulations will be used to determine how salinity and nutrients affect the distribution, growth and activity of specific N2 fixing populations using a molecular biology approach. The results of these experiments will provide new information on the regulation of productivity and algal bloom-formation in estuaries, freshwaters, and the marine environment.