Dissertation Research: Closing the nitrogen budget: Quantifying denitrification in an arid ecosystem undergoing nitrogen enrichment

从肥料、沉积物或固氮植物中添加活性氮到生态系统中会导致人类不希望看到的快速且往往有害的变化。通过反硝化过程产生二氮气体（N2）是从生态系统中去除活性氮的主要机制。然而，这个过程也会产生一氧化二氮（N2O），一种温室气体。因此，了解反硝化过程中产生的N2和N2O的数量对于理解气候和生态系统的营养平衡至关重要。在现实世界中研究反硝化的挑战之一是很难测量现场的N2产量。本文提出的工作将利用一种新的实验室测量技术来测量土壤中N2的产生，并研究固氮树在干旱的亚热带草原扩张后反硝化作用、N2和N2O的产生和氮循环的变化。干旱地区占地球表面的近三分之一，养活着大量人口，因此了解这些系统中氮的处理对未来的土地利用和全球气候管理非常重要。该项目将提供干旱系统氮循环中反硝化过程中N2损失的首次估计，并有助于改进可应用于其他地点和生态系统的方法。在这个项目中使用的主要研究地点是德克萨斯州南部一个活跃的养牛场，学生、土地管理者和自然爱好者经常访问这个牧场。该项目将利用这一公共界面来教育人类驱动的景观变化对生态系统养分循环的影响和重要性。

Adding reactive nitrogen, from fertilizer, deposition, or nitrogen fixing plants, to ecosystems can cause rapid and often detrimental changes considered undesirable by humans. The creation of dinitrogen gas (N2) through a process called denitrification is the primary mechanism that removes reactive nitrogen from an ecosystem. However, this process can also produce nitrous oxide (N2O), a greenhouse gas. Therefore, understanding how much N2 versus N2O is produced during denitrification is critical to understanding both climate and ecosystem nutrient balance. One of the challenges of studying denitrification in the real world is that it is very difficult to measure the production of N2 in the field. The work proposed here will take advantage of a new lab measurement technique to measure the production of N2 from soils and examine how denitrification, N2 and N2O production and nitrogen cycling change after the expansion of a nitrogen-fixing trees into an arid subtropical grassland.Arid lands occupy nearly a third of the Earth's surface and support large human populations, so understanding the processing of nitrogen in these systems is important for future land use and global climate management. This project will provide the first estimate of the N2 loss occurring during denitrification in an arid system nitrogen cycle, and help to refine a method that can then be applied to other sites and ecosystems. The primary research site used in this project is an active cattle ranch in Southern Texas that is regularly visited by students, land managers and nature enthusiasts. This project will take advantage of this public interface to educate on the effects and importance of human-driven landscape changes on ecosystem nutrient cycling.