SOIL EMISSIONS OF NITRIC-OXIDE IN A SEASONALLY DRY TROPICAL FOREST OF MEXICO

Soil emissions of NO were measured at the Chamela Biological Station, Mexico, using soil covers and a field apparatus for NO detection based on CrO3 conversion of NO to NO2 and detection of NO2 by chemiluminescence with Luminol. Mean NO fluxes from forest soils ranged from 0.14 to 0.52 ng NO-N cm-2 hr-1 during the dry season and from 0.73 to 1.27 ng NO-N cm-2 hr-1 during the wet season. A fertilized floodplain pasture exhibited higher fluxes, but an unfertilized upland pasture, which represents the fastest growing land use in the region, had flux rates similar to the forest sites. Wetting experiments at the end of the dry season caused large pulses of NO flux, equaling 10% to 20% of the estimated annual NO emissions of 0.5-1.0 kg N ha-1 from the forest sites. Absence of a forest canopy during the dry season and the first wet season rain probably results in substantial NO(x) export from the forest system that may be important to regional atmospheric chemical processes. Wetting experiments during the wet season and a natural rain event had little or no stimulatory effect on NO flux rates.