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

向生态系统中添加来自化肥、沉积物或固氮植物的活性氮会导致人类认为不受欢迎的快速且往往是有害的变化。通过一个称为反硝化的过程产生氮气(N2)是从生态系统中去除活性氮的主要机制。然而，这一过程也会产生温室气体一氧化二氮(N2O)。因此，了解在反硝化过程中产生多少氮气和N2O对于理解气候和生态系统养分平衡是至关重要的。在现实世界中研究反硝化的挑战之一是，很难在野外测量氮气的产量。这项工作将利用一种新的实验室测量技术来测量土壤中氮气的产生，并研究在固氮树木扩展为干旱的亚热带草原后，反硝化作用、氮气和N2O的产生以及氮循环的变化。干旱土地占据了地球表面近三分之一的面积，并养活了大量的人口，因此了解这些系统中氮素的过程对于未来的土地利用和全球气候管理非常重要。该项目将提供对干旱系统氮循环中反硝化过程中氮气损失的第一次估计，并有助于改进一种方法，然后将其应用于其他地点和生态系统。该项目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、土地管理人员和自然爱好者定期访问该牧场。该项目将利用这一公共界面，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.