Some Factors Limiting Denitrification in Slurries of Acid Forest Soils

Denitrifying enzyme activity (DEA) is defined as N2O production rate over the first eight hours of anaerobic incubation of soil slurries at 15 degrees C with added nitrate and acetylene. Organic fraction explained 81 % of the spatial variation in DEA among soil horizons of beech (Fagus), alder (Alnus), and spruce (Picea) forests, and spruce clearcuts. Nitrate and pH limit denitrification in anaerobic O horizons at 15 degrees C. Thick, poorly drained O horizons, such as in alder forest, have a high capability for denitrification. Failure to recover all added nitrate in O horizon incubations suggested both production of unmeasured NO and dissimilatory reduction of nitrate to ammonium. In mineral horizons, N2O production was small and could not be increased by increasing nitrate, carbon, pH, and phosphorus; some other factor appears to prevent significant denitrifier activity in acid forest mineral horizons.