Oxygen Consumption and Denitrification Activity of a Conifer Forest Soil Profile

Abstract

AbstractForest soil profile samples (L‐H, 0–5, 5–15, 15–30, 30–60 cm depths) were collected from a Douglas‐fir [Pseudotsuga menziesii (Mirb.) Franco] plantation in British Columbia. These soil samples were incubated at 20°C in the presence of (15NH2)2CO, Ca(15NO3)2, and Na15NO2 to investigate the biological activity, expressed as oxygen consumption rate (O2CR), carbon dioxide production rate (CO2PR), and potential denitrification (both biological and chemical) activity under controlled conditions in the laboratory. The gaseous samples were analyzed mass spectrometrically. The O2CR of the L‐H sample was high (29.0 µg g−1 h−1) and decreased with depth in the mineral soil (2.9 µg g−1 h−1 at 30–60‐cm depth). The CO2PR followed the pattern of O2CR, indicating they are related. Denitrification depended on the N‐source. When Ca(15NO3)2 (100 mg N L−1) was applied to the L‐H samples, the NO‐3 was denitrified to N2O and N2 under anaerobic conditions. The quantity and percentage of applied‐N from Ca(15NO3)2 denitrified over the 168‐hour period decreased with increasing depth. When Na15NO2 (400 mg N L−1) was added to the L‐H samples, N2O and N2 were detected under aerobic conditions. The N2 production appeared to be the result of both chemical and biological denitrification. Denitrification was not detected when (15NH2)2CO (500 mg N L−1) was incubated with L‐H and 0 to 5‐cm soil profile samples under aerobic condition.