CONTRIBUTION OF NITRIFICATION AND DENITRIFICATION TO THE NO AND N2O EMISSIONS OF AN ACID FOREST SOIL, A RIVER SEDIMENT AND A FERTILIZED GRASSLAND SOIL

Most studies determining the contribution of nitrification and denitri fication to NO and N2O emissions from soils have been performed in agr icultural systems, often with homogenized soil samples. More informati on about the nitrifier and denitrifier contribution in non-agricultura l systems may increase the accuracy of global NO and N2O emission esti mates. We assessed the contributions of nitrification and denitrificat ion to NO and N2O emissions from three different ecosystems: an acid f orest soil; a river sediment in the intertidal zone; and a fertilized peat grassland, using intact soil cores. Samples were taken in the spr ing 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 denitri fication contribution was determined by specific inhibition of nitrifi cation. 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 fo rest soil and grassland soil in the autumn. However, the tight couplin g of nitrification and denitrification in the river sediment could hav e resulted in an over-estimation of the contribution of nitrification to N2O and NO production. A large part of denitrified N in the acid fo rest soil was emitted as N2O, whereas in the river sediment, except fo r the autumn, the denitrification N2O-to-N-2 ratio was low, which coin cided with a low nitrate content. Nitrification was the dominant NO so urce in spring at all sites. In autumn, high contributions of both nit rification and denitrification were observed. (C) 1997 Elsevier Scienc e Ltd.