Nitrogen mineralization and potential nitrification at different depths in acid forest soils

摘要: Soil samples were collected from the litter, humus and five mineral soil layers to a depth of 50 cm in acid, but highly productive, Norway spruce forests S Sweden E Denmark for determination net N mineralization potential nitrification. The sieved while still fresh incubated at constant temperature (15°C) moisture 74–117 days with periodic subsamplings. Net rates, expressed per g organic matter or total N, decreased increasing depth. ten soils studied ranged 35 105 kg ha-1 yr-1, which horizons contributed 32–74%. Nitrate formation patterns variable. Almost no nitrification could be detected pH (H2O) values lower than 4.0. was formed 4.0–4.5, never complete. By contrast, almost complete 10–50 cm, where 4.1–4.5. Addition CaCO3 stimulated layer, indicating presence acid-sensitive nitrifiers, sometimes inhibited by addition CaCO3. Tests acetylene block method showed that nitrification, when it occurred, autotrophic layer less easy characterize soil. Thus, further studies are needed nitrifier organisms identify factors regulating activity these organisms. Actual rates field not determined, our findings B horizon acid forest has great Because deposition does appear decrease Scandinavian forests, we conclude an ammonium surplus floor followed downward transport nitrifying subsoil can increase risk nitrate leaching future.