Contribution of nitrification and denitrification to the NO and N2O emissions of an acid forest soil, a river sediment and a fertilized grassland soil

Abstract

Most studies determining the contribution of nitrification and denitrification to NO and N₂O emissions from soils have been performed in agricultural systems, often with homogenized soil samples. More information about the nitrifier and denitrifier contribution in non-agricultural systems may increase the accuracy of global NO and N₂O emission estimates. We assessed the contributions of nitrification and denitrification to NO and N₂O emissions from three different ecosystems: an acid forest soil; a river sediment in the intertidal zone; and a fertilized peat grassland, using intact soil cores. Samples were taken in the spring of 1993 and the autumn of 1994. Intact soil cores (5 cm deep) were incubated at field temperature in the laboratory and the accumulation of NO and N₂O during 24 h was measured. The nitrification and denitrification contribution was determined by specific inhibition of nitrification. The highest mean N₂O production was in the same range for all sites. Nitrification dominated N₂O production in spring at all sites. In contrast, denitrification was the main source of N₂O in the acid forest soil and grassland soil in the autumn. However, the tight coupling of nitrification and denitrification in the river sediment could have resulted in an over-estimation of the contribution of nitrification to N₂O and NO production. A large part of denitrified N in the acid forest soil was emitted as N₂O, whereas in the river sediment, except for the autumn, the denitrification N₂O-to-N₂ ratio was low, which coincided with a low nitrate content. Nitrification was the dominant NO source in spring at all sites. In autumn, high contributions of both nitrification and denitrification were observed.