CAREER: The biological nitrogen isotope systematics of ammonium consumption and production

海洋环境中的氮循环受生物过程控制。不幸的是，由于空间和时间差异很大，很难通过直接测量来量化这些过程并评估它们对N循环的影响。氮的同位素组成测量提供了一种间接约束这些过程的手段；然而，通过生物过程对循环氮的同位素分馏仍有很多了解，这给解释新的氮同位素数据带来了困难。康涅狄格大学的一名研究人员计划确定生物消耗和生产对铵中同位素分馏的影响。通过在生物水平上帮助理解循环铵的分离过程，这项研究将为未来的研究人员更好地解释同位素组成数据以推断氮循环动力学奠定基础。一名研究生、一名博士后和两名或两名以上本科生将参与研究。该研究人员计划通过开发本科领域和实验室课程，将科学与社区参与的学习结合起来，这将要求学生向社区的利益相关者展示他们的研究。将为这门课程编写一份手册，并在开放获取论坛上分发给希望开发类似课程的教师。尽管近年来出现了各种分析氮同位素的新技术，但与氮循环相关的生物氮同位素分馏仍然受到很差的限制。同位素组成数据的使用对于解释海洋中难以直接测量的氮循环过程非常有用，这使得进一步了解分馏背后的过程以赶上研究人员可用数据集的进步至关重要。本研究将表征氨在生物消耗和生产过程中的同位素分馏动态。研究人员将研究海洋表面低浓度铵的特征是否会影响铵回收时的同位素分异，以及原生动物食草动物对铵的回收是否存在营养同位素效应。通过这项研究，研究人员可以从铵同位素数据集中解释再循环氮动力学。有了这样一个标准，比较氮循环研究的方法将变得更加清晰，通过消除显著的不确定性，使解释变得统一。

The nitrogen (N) cycle in the marine environment is controlled by biological processes. Unfortunately, quantifying these processes and assessing their effect on the N cycle is difficult by direct measurements because of large spatial and temporal differences. Isotopic composition measurements of N provide a means to constrain these processes indirectly; however, there is still a great deal to be understood about isotope fractionation of recycled nitrogen through biological processes, which has made interpretation of novel nitrogen isotope data difficult. A researcher from the University of Connecticut plans to determine the influence of biological consumption and production on the isotope fractionation in ammonium. By helping to understand the processes surrounding fractionation of recycled ammonium at the organism level, this research will create a basis for which future researchers can better interpret isotope composition data to infer nitrogen cycle dynamics. A graduate student, a postdoctoral fellow, and two or more undergraduate students will be involved in the research. The researcher plans to integrate science with community-engaged learning by developing an undergraduate field and laboratory course that will require the students to present their research to stakeholders in the community. There will be a manual created for this course that will be disseminated in open-access forums for teachers hoping to develop similar courses. Biological nitrogen isotope fractionation associated with nitrogen recycling remains poorly constrained despite the advent of a variety of new techniques to analyze nitrogen isotopes in recent years. The use of isotopic composition data can be incredibly useful to interpreting nitrogen cycle processes in the ocean that are difficult to measure directly, which makes it crucial to further understand the processes behind fractionation to catch up with the advancement of the datasets available to researchers. This research will characterize the isotope fractionation dynamics of ammonium during biological consumption and production. The researchers will investigate whether the characteristic low concentrations of ammonium in the surface ocean affect isotope fractionation when the ammonium is recycled and whether there is a trophic isotope effect associated with ammonium recycling by protozoan grazers. With this research, there will be a baseline from which researchers can interpret recycled nitrogen dynamics from ammonium isotope datasets. The methods of comparing nitrogen cycling studies will become significantly clearer with such a standard making interpretation uniform by removing significant uncertainties.