DENITRIFYING POTENTIAL AND ENZYME-ACTIVITY IN A NORWAY SPRUCE FOREST

In an approximately 100-year-old Norway spruce forest on brown earth (cambisol) the denitrification potential was determined in laboratory incubation studies at 24-degrees-C in relation to soil depth as well as carbon and nitrogen availability. Denitrification rates were highest (344-mu-g N2O kg-1 dry wt. day-1) in the top 10 cm of intact soil cores (7 cm diameter), and increased when glucose (3.4-fold) or nitrate (1.8-fold) were added. At a soil depth of 10-20 or 20-30 cm, N2O release was significantly smaller than in the topsoil layer (0-10 cm), and was stimulated by the addition of glucose rather than nitrate. This indicates that at greater soil depth denitrification is carbon rather than nitrogen limited. Assessment of the denitrifying enzyme activity for the upper (0-9 cm) soil layer has revealed that this is much higher in the O(f)O(h)-horizon (1.81-mu-g N2O g-1 dry wt. h-1) than in the A(h)-horizon (0.91-mu-g N2O g-1 dry wt. h-1).