Nitrogen mineralization and water-table height in oligotrophic deep peat

Summary Peat cores, 0–60 cm depth, were taken on 14 occasions from three experimental plots where the water levels in the surrounding ditches had been artificially controlled for 14 years at 0, 20 and 50 cm below the surface. Numbers of aerobic and anaerobic ammonifying bacteria in the profile were significantly increased (P< 0.05) by lowering the water level from 0 to 50 cm. These increases occurred mainly in the surface 20 cm horizon, where 80%–90% of the ammonifying bacteria in the profile occurred. Mineral N in fresh samples, which was present almost entirely as ammonium, decreased sharply with depth below 20 cm, and on two occasions concentrations were significantly greater (P<0.05) in plots with water levels at 20 and 50 cm than in the flooded peat. Readily mineralized N, produced during waterlogged incubation at 30°C for 9 weeks, was significantly greater (P<0.05) on eight occasions in samples from plots with water levels at 20 or 50 cm than in those where the water level was at the surface. Calculations showed that the increases in N availability as a result of lowering the water-table could be attributed mainly to deeper rooting.