Instantaneously Identifying Biological Sources of Nitrous Oxide Flux from Agricultural Soils via Position Specific Nitrogen Stable Isotope Compositions

Abstract:

Nitrous oxide (N₂O), a greenhouse gas, is produced by multiple biological reactions but their relative contributions in agricultural soils is unknown, preventing loss minimization. We hypothesized that creating favorable environmental conditions for one of these processes, denitrification, will lead to enhanced N₂O loss. This was achieved in a field study by adding water to create an anerobic soil environment of 80% water filled pore space and monitoring N₂O flux using an automated chamber system connected to a cavity laser absorption spectroscopy system with capabilities to measure site-specific nitrogen stable isotope compositions of N₂O. We predicted that differences would indicate the biological sources of N₂O. Results showed that biological processes contributing to N₂O flux were (etc) driven by water application, natural precipitation events, and changes in soil temperature. Site-specific ẟ¹⁵N analysis of terminal and central N in the N₂O molecule indicate that denitrification is the main process responsible for increased N₂O flux as soil temperature decreases or following precipitation events. In contrast, nitrification is the dominant producer of N₂O with increased temperature and decreased soil water. These findings are novel as they monitor real time, relative contributions of biological processes responsible for soil N₂O flux. Additionally, biological communities responsible for nitrification and denitrification are highly influenced by soil temperature and water, respectively. There is still a fundamental lack in knowledge about which soil microbial populations are responsible and their relative contributions to N₂O flux in field settings. The ability to trace N₂O to its biological origins and identify environmental impacts on biological populations will aid the scientific community’s understanding of drivers behind critical soil N cycle processes.