NITROGEN TRANSFORMATIONS AND NITROUS-OXIDE FLUX IN A TROPICAL DECIDUOUS FOREST IN MEXICO

Emissions of nitrous oxide and soil nitrogen pools and transformations were measured over an annual cycle in two forests and one pasture in tropical deciduous forest near Chamela, Mexico. Nitrous oxide flux was moderately high (0.5-2.5 ng cm-2 h-1) during the wet season and low (< 0.3 ng cm-2 h-1) during the dry season. Annual emissions of nitrogen as nitrous oxide were calculated to be 0.5-0.7 kg ha-1 y-1, with no substantial difference between the forests and pasture. Wetting of dry soil caused a large but short-lived pulse of N2O flux that accounted for < 2% of annual flux. Variation in soil water through the season was the primary controlling factor for pool sizes of ammonium and nitrate, nitrogen transformations, and N2O flux.