EFFECTS OF NITROGEN-FERTILIZATION ON THE FLUXES OF N2O, CH4, AND CO2 FROM SOILS IN A FLORIDA SLASH PINE PLANTATION

We measured fluxes of N2O, CH, and CO2 from control and urea-nitrogen fertilized soils of a mature slash pine (Pinus elliottii var. elliotti i Englem.) plantation in Alachua County, Florida. The fertilization di d not affect CO2 emissions, but significantly increased the emissions of N2O and lowered the uptake of atmospheric CH4. Daily average N2O em issions from the fertilized soils were 8-600 times higher (12-74 mug N 2O-N.m2.h-1) than daily average N2O emissions from control soils (0.02 -4.0 mug N2O-N.m-2.h-1). Daily average CH4 uptake by the fertilized so ils were 5-20 times lower (0.001-0.007 mg CH4-C.m-2.h-1) than daily av erage CH4 uptake by control soils (0.015-0.035 mg CH4-C.m-2.h-1). We a lso measured the relative activities of the bacteria populations that were responsible for CH4 oxidation in the control and fertilized soils . Results from these measurements suggest that fertilization shifted t he relative activities of the CH4 oxidizing bacteria from those domina ted by methanotrophs in the control soils to those dominated by nitrif ying bacteria in the surface (0-2 cm) of the fertilized soils. The shi ft in relative activities of these bacteria may have been responsible for the lower CH4 uptake by the fertilized soils.