Expression of Microbial Nitrification in the Stable Isotopic Systematics of Oceanic Nitrite and Nitrate

减少硝酸盐和一氧化二氮的海洋预算是研究人员的中心目标，他们对营养驱动的初级生产力变化和气候变化感兴趣。随着海水硝酸盐氧同位素分析新方法的实施，将有可能根据硝酸盐的氧同位素分布来编制与氮同位素预算相辅相成的硝酸盐预算。在我们能够有效地利用硝酸盐中的氧同位素来了解目前对海洋氮循环的理解之前，我们必须首先了解产生(硝化)和消耗(同化、反硝化)硝酸盐的不同过程如何影响其氧同位素特征。在这项研究中，伍兹霍尔海洋研究所的研究人员将对野外硝化作用的氧同位素系统学进行定量评估，从而填补我们在理解硝酸盐、亚硝酸盐和一氧化二氮18O变化方面的一个关键空白。主要目标是对海洋硝化过程中产生的亚硝酸盐和硝酸盐的氧同位素特征进行定量预测。研究人员假设，硝化过程中的氧同位素分馏是决定新产生的硝酸盐和亚硝酸盐的18O值的主要因素。其次，他们假设，在氨氧化和亚硝酸盐氧化紧密耦合的地方，氧原子交换很低，但在亚硝酸盐积累的区域，如初级和次级亚硝酸盐最大值，氧原子交换可能增加。他们将通过一系列有针对性的实验室和野外实验，以及通过测量东热带南太平洋真光带、初级亚硝酸盐最大值和次要亚硝酸盐最大值的亚硝酸盐和硝酸盐同位素分布来验证这些假设。这些实验的结果有望提供在基础微生物过程中解释亚硝酸盐、硝酸盐和N2O中的18O同位素特征所需的基本信息。更好地了解这些特征和涉及的过程对于量化新的产量、对N预算的控制和海洋中的N2O产生非常重要--这将导致更好地理解氮循环、海洋化学和气候之间的直接和间接相互作用。更广泛的影响：这项研究的结果应该会引起对海洋氮循环、N2O产生和气候变化以及硝化菌生理和生物化学感兴趣的广泛研究团体的兴趣。生物地球化学方面的学生培训将是该活动的一个重要组成部分。一名女研究生将参与整个项目，并将学习如何整合培养操作、实验室和实地研究以及同位素和数据获取和分析方面的培训。本科生，包括来自代表不足的少数群体的学生，也将有机会参与进来。

Closing the marine budgets of nitrate and nitrous oxide are central goals for researchers interested in nutrient-driven changes in primary productivity and climate change. With the implementation of new methods for oxygen isotopic analysis of seawater nitrate, it will be possible to construct a budget for nitrate based on its oxygen isotopic distribution that is complementary to nitrogen isotope budgets. Before we can effectively use oxygen isotopes in nitrate to inform the current understanding of the marine nitrogen cycle, we must first understand how different processes that produce (nitrification) and consume (assimilation, denitrification) nitrate affect its oxygen isotopic signature. In this study, researchers at the Woods Hole Oceanographic Institution will provide a quantitative assessment of the oxygen isotopic systematics of nitrification in the field and thus fill a key gap in our understanding of 18O variations in nitrate, nitrite, and nitrous oxide. The primary goal is to develop a quantitative prediction of the oxygen isotopic signatures of nitrite and nitrate produced during nitrification in the sea. The researchers hypothesize that oxygen isotopic fractionation during nitrification is the primary factor setting the 18O values of newly produced nitrate and nitrite. Secondly, they hypothesize that oxygen atom exchange is low where ammonia oxidation and nitrite oxidation are tightly coupled, but may increase in regions with nitrite accumulation, such as in the primary and secondary nitrite maxima. They will test these hypotheses with a series of targeted laboratory and field experiments, as well as with measurements of nitrite and nitrate isotopic distributions extending through the euphotic zone, primary nitrite maximum, and secondary nitrite maximum of the Eastern Tropical South Pacific. The results of these experiments are expected to provide fundamental information required for the interpretation of 18O isotopic signatures in nitrite, nitrate, and N2O in the context of underlying microbial processes. A better understanding of these features and the processes involved is important for quantifying new production, controls on the N budget, and N2O production in the ocean -- which should lead to a better understanding of the direct and indirect interactions among the nitrogen cycle, marine chemistry, and climate. Broader Impacts: The results of this research should be of interest to a broad research community interested in oceanic nitrogen cycling, N2O production, and climate change, as well as nitrifier physiology and biochemistry. Student training in biogeochemistry will be an important component of the activity. A female graduate student will participate throughout this project, and will learn to integrate training in culture manipulation, laboratory and field-going research, as well as isotopic and data acquisition and analysis. There will also be opportunities for undergraduate students, including ones from under-represented minority groups, to become involved.