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

[摘要] An open-top-chamber (OTC)CO₂ enrichment (~720 mmolmol^-1) study was conducted in the Colorado shortgrass steppe from April 1997 through October 2001.Aboveground plant biomass increased under elevated CO₂ and soil moisture content wastypically higher than under ambient CO₂ conditions.Fluxes ofCH₄, CO₂,NO_x and N₂O,measured weekly year round were not significantly altered by CO₂ enrichment over the 55month period of observation.During early summer of 2002, following the removal of theopen-top-chambers from the CO₂ enrichment sites in October 2001, we conducted a shortterm study to determine if soil microbial processes were altered in soils that had been exposedto double ambient CO₂ concentrations during the growing season for the past five years.Microplots were established within each experimental site and 10 mm of water or10 mm of water containing the equivalent of 10 g m^-2 of ammonium nitrate-N was applied to the soilsurface. Fluxes of CO₂,CH₄, NO_x and N₂O fluxes within control(unchambered), ambient CO₂ and elevatedCO₂OTC soils were measured at one to three day intervals for the nextmonth. With water addition alone, CO₂ and NO emission did not differ between ambient andelevated CO₂ soils, whileCH₄ uptake rates were higher and N₂O fluxes lower in elevatedCO₂soils.Adding water and mineral N resulted in increased CO₂ emissions, increasedCH₄ uptake and decreased NO emissions in elevated CO₂ soils.The N addition study confirmedprevious observations that soil respiration is enhanced under elevated CO₂ and Nimmobilization is increased, thereby decreasing NO emission.

[学科分类] 大气科学