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Brown JR. 2011. Interactive global changes, wildfire, and soil N2O emissions. Master's thesis, Department of Biological Sciences, Northern Arizona University.
Year Published: 2011

Global environmental changes are expected to alter ecosystem carbon and nitrogen cycling, but the interactive effects of multiple simultaneous environmental changes are poorly understood. Effects of global change on the production of nitrous oxide (N2 O) by soils could feed back to climatic change, as N2 O is an important greenhouse gas. I assessed the responses of in situ soil N2 O fluxes to elevated CO 2 , warming, altered precipitation, and enhanced nitrogen (N) deposition, as well as their interactions, in annual grassland plots at the Jasper Ridge Global Change Experiment (CA, USA). Measurements were conducted 6, 7 and 8 years after treatments started, at the end of each of the three growing seasons--in April 2004, 2005 and 2006. Elevated precipitation altered N 2 O flux, but effects were variable over time. Elevated precipitation increased N 2 O efflux in April of 2006, the sampling event with the highest overall soil water content.In June of 2003, an accidental fire swept through part of the Jasper Ridge Global Change Experiment. We took advantage of this natural grassland ecosystem process to examine the interactive effects of wild fire, elevated CO2 , altered precipitation, and enhanced N nitrogen deposition on soil N2 O emissions. In situ N2 O measurements were conducted 9, 15, 19, 21, and 33 months after the fire. I found that wild fire significantly increased N2 O soil emissions throughout the three-year period following the fire. The effect of greater N2 O soil emissions with wild fire was enhanced when combined with elevated CO2 and nitrogen.Accurately predicting greenhouse gas emissions from soils is an important part of understanding ecosystem feedbacks to global change. My results from both experiments stress the importance of multiple global change interactions as well as the incorporation of natural ecosystem disturbances on soil N 2 O emissions.