N mineralization, nitrification, and N uptake across a 100-year chronosequence of upland hardwood forests

Net N mineralization, nitrification, and N uptake were monitored in the A (0-8 cm) and B (8-30 cm) soil horizons from 1997 to 1999 across a chronosequence of upland hardwood forest stands in southern Indiana, USA. Stand ages were 1, 6, 12, 3 1, and 80-100 years at the beginning of the study. Contrary to previous studies, there was no apparent stimulation of N mineralization due to harvesting. The highest rates of N mineralization, nitrification, and N uptake were in the mature forest stand. Rates of N cycling were greater in the A than the B horizon by concentration (g kg(-1)), but the greater depth and bulk density of the B horizon led to insignificant differences by area (kg ha(-1)). N mineralization, nitrification, and N uptake all correlated significantly with each other, and average annual rates of N mineralization balanced well with N uptake in most stands of the chronosequence. N cycling seemed to be subject to strong internal regulation at all stages of stand development. Analyses of the spatial and temporal variability in N cycling properties or processes would provide further insights in the effects of harvesting on N cycling in these forest stands. (C) 2002 Elsevier Science B.V. All rights reserved.