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

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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.