Jamie R. Brown, Paul Dijkstra, Joseph C. Blankinship, Jeffery S. Coyle, and Bruce A. Hungate. Northern Arizona University
Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are powerful greenhouse gasses driving global change. As global atmospheric concentrations of CO2, CH4, and N2O increase, in-situ terrestrial flux measurements of these gasses are an important part of quantifying sources and sinks as well as determining positive or negative feedbacks. We assessed responses of soil fluxes of CO2 (soil respiration), CH4, and N2O to elevated temperature and altered precipitation treatments along the C. Hart Merriam Elevation Gradient Transect in Northern Arizona during a monsoon season. We found significant increases in soil respiration and N2O efflux, and a decrease in CH4 oxidation (uptake) in response to increasing elevation and precipitation. We found that warming of ~3 °C in the mixed conifer ecosystem removed temperature limitations on production of N2O and CO2, and that CH4 oxidation was not temperature dependent. We also found that altering precipitation within ecosystems influenced fluxes of all three gasses. As soil moisture increased, soil respiration and N2O efflux increased, while CH4 oxidation appeared to become limited by diffusion of CH4 and/or oxygen. Overall, we found that the increase in temperature and precipitation predicted for Northern Arizona during the monsoon season will result in an increase in soil respiration and N2O production and a decrease in CH4 oxidation by soils. These changes constitute a positive feedback for all three gasses in response to the climatic changes caused by increasing atmosphere concentrations of CO2, N2O, and CH4.