Effect of water addition and nitrogen fertilization on the fluxes of CH4, CO2, NOx, and N2O following five years of elevated CO2 in the Colorado Shortgrass Steppe

Other literature type English OPEN
Mosier, A. R. ; Pendall, E. ; Morgan, J. A. (2003)

An open-top-chamber (OTC) CO<sub>2</sub> enrichment (~720 <font face="Symbol" >m</font>mol mol<sup>-1</sup>) study was conducted in the Colorado shortgrass steppe from April 1997 through October 2001. Aboveground plant biomass increased under elevated CO<sub>2</sub> and soil moisture content was typically higher than under ambient CO<sub>2</sub> conditions. Fluxes of CH<sub>4</sub>, CO<sub>2</sub>, NO<sub>x</sub> and N<sub>2</sub>O, measured weekly year round were not significantly altered by CO<sub>2</sub> enrichment over the 55 month period of observation. During early summer of 2002, following the removal of the open-top-chambers from the CO<sub>2</sub> enrichment sites in October 2001, we conducted a short term study to determine if soil microbial processes were altered in soils that had been exposed to double ambient CO<sub>2</sub> concentrations during the growing season for the past five years. Microplots were established within each experimental site and 10 mm of water or 10 mm of water containing the equivalent of 10 g m<sup>-2</sup> of ammonium nitrate-N was applied to the soil surface. Fluxes of CO<sub>2</sub>, CH<sub>4</sub>, NO<sub>x</sub> and N<sub>2</sub>O fluxes within control (unchambered), ambient CO<sub>2</sub> and elevated CO<sub>2 </sub>OTC soils were measured at one to three day intervals for the next month. With water addition alone, CO<sub>2</sub> and NO emission did not differ between ambient and elevated CO<sub>2</sub> soils, while CH<sub>4</sub> uptake rates were higher and N<sub>2</sub>O fluxes lower in elevated CO<sub>2</sub> soils. Adding water and mineral N resulted in increased CO<sub>2</sub> emissions, increased CH<sub>4</sub> uptake and decreased NO emissions in elevated CO<sub>2</sub> soils. The N addition study confirmed previous observations that soil respiration is enhanced under elevated CO<sub>2</sub> and N immobilization is increased, thereby decreasing NO emission.
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