15N Isotopomeric Site Preferences and Enrichment Factors for Nitrification and Denitrification: A New Constraint to the N2O Global Budget

硝化和反硝化的 15N 同位素位点偏好和富集因子：N2O 全球预算的新约束

• 批准号: 0312004
• 负责人: Stanley Tyler
• 金额: $ 16.22万
• 依托单位: University of California-Irvine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-08-15 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0312004&HistoricalAwards=false
• 关键词: 15N; Isotopomeric; Site; Preferences; Enrichment

Nitrous oxide (N2O) is both an important greenhouse gas and as a source of NO in the stratosphere. The amount of N2O in the atmosphere has increased during the past century, though the reasons for that increase remain uncertain. Different sources adding N2O to the atmosphere may be distinguished if they have different stable isotope signatures. In soils, the largest natural source of N2O, we have shown that the isotopic signature of N2O depends on both the availability of N substrates and whether the main process producing N2O is nitrification or denitrification. The microbial processes in turn are linked to soil moisture and temperature conditions. Based on our previous work, we hypothesize that much of the increase in N2O over the past few decades has been fueled by increased use of nitrogen fertilizers in agriculture, which in turn stimulates the emission of N2O, primarily through nitrification. This work will explore the role of fertilizer addition to agricultural soils on N2O emissions, using the isotope signatures of N2O and its precursor compounds in urea-amended soil to understand which microbial pathways are responsible for producing N2O, and how those pathways vary with soil moisture conditions. We will work in a temperate (North Carolina) and a tropical (Venezuela) agricultural setting. Specific hypotheses to be tested include: (1) nitrification and denitrification have very different isotopic fractionation factors (including positional dependence of the 15N within the N2O molecule), allowing us to quantify in a given soil what fraction of the N2O emitted was produced by each process; (2) soils fertilized with urea versus nitrate or organic nitrogen will have very different isotopic fingerprints in emitted N2O, even from the same soil; (3) temperate and tropical agricultural soils will differ in both the rate and isotopic signature of N2O emissions following fertilizer use. To test these hypotheses, we will: (1) develop and apply methods to determine the isotope fractionation factors characteristic (15N and 18O contents, as well as the bond in the N2O molecule which contains the 15N); (2) develop the method for measuring the positional dependence of 15N in the N2O molecule at the stable isotope facility at UC Irvine; and (3) make initial assessments of how the isotopic signatures of N2O emitted from agricultural soils in temperate (North Carolina) and tropical (Venezuela) sites differ when the same type of fertilizer is applied (urea).to soils with different soil water content. Our results will provide a greater understanding of the processes resulting in N2O emissions, and hence will be of use for managing fertilizer application so as to minimize future N2O emissions.

一氧化二氮（N2 O）是平流层中一种重要的温室气体，也是一氧化氮的来源。 在过去的世纪里，大气中的N2 O含量有所增加，但增加的原因仍然不确定。 如果不同的来源具有不同的稳定同位素特征，则可以区分向大气中添加N2 O的不同来源。在土壤中，N2 O的最大的天然来源，我们已经表明，N2 O的同位素签名取决于氮基质的可用性和是否产生N2 O的主要过程是硝化或反硝化。 微生物过程反过来又与土壤湿度和温度条件有关。根据我们以前的工作，我们假设，在过去的几十年中，N2 O的增加主要是由于农业中氮肥的使用增加，这反过来又刺激了N2 O的排放，主要是通过硝化作用。 这项工作将探讨肥料添加到农业土壤中对N2 O排放的作用，使用尿素修正土壤中N2 O及其前体化合物的同位素特征来了解哪些微生物途径负责产生N2 O，以及这些途径如何随土壤水分条件而变化。我们将在温带（北卡罗来纳州）和热带（委内瑞拉）农业环境中工作。 有待检验的具体假设包括：（1）硝化和反硝化具有非常不同的同位素分馏因子（包括15 N在N2 O分子中的位置依赖性），使我们能够量化给定土壤中每种过程产生的N2 O排放量;（2）施用尿素的土壤与施用硝酸盐或有机氮的土壤在排放的N_2O中具有非常不同的同位素指纹，即使来自同一土壤;（3）温带和热带农业土壤在施用化肥后N2 O排放的速率和同位素特征方面存在差异。为了验证这些假设，我们将：（1）发展和应用确定同位素分馏因子特征的方法（2）在加州大学欧文分校的稳定同位素设施上开发了测量N2 O分子中15 N的位置依赖性的方法;（3）初步评估当同一类型的肥料（尿素）施于不同土壤含水量的土壤时，温带（北卡罗来纳州）和热带（委内瑞拉）地区农业土壤排放的N2 O的同位素特征是如何不同的。 我们的研究结果将提供一个更好的了解过程中产生的N2 O排放，因此将用于管理施肥，以尽量减少未来的N2 O排放。