CANOPY TREE–SOIL INTERACTIONS WITHIN TEMPERATE FORESTS: SPECIES EFFECTS ON SOIL CARBON AND NITROGEN

Abstract

In a northwestern Connecticut forest, we quantified the carbon (C) and nitrogen (N) content of the forest floor and the top 15 cm of mineral soil and the rate of midsummer net N mineralization beneath six different tree species. There were large interspecific differences in forest floor depth and mass, in the size and distribution of C and N pools at varying soil depths, and in rates of midsummer net N mineralization and nitrification. Forest floor mass ranged from 3.2 kg/m2 to 11.0 kg/m2 and was smallest beneath sugar maple and largest beneath hemlock. The pool size of C in the forest floor ranged from 1.1 kg/m2 to 4.4 kg/m2 while the N content of the forest floor ranged from 83 g/m2 to 229 g/m2. Forest floor C and N pools were smallest beneath sugar maple and highest beneath hemlock. Soil C:N ratios (range: 14.8–19.5) were lower beneath sugar maple, red maple, and white ash than beneath beech, red oak, and hemlock, whereas the opposite was true of the midsummer rate of net N mineralization (range: 0.91–2.02 g·m−2·28 d−1). The rate of net nitrification was positively correlated with the rate of net N mineralization. Interspecific differences in litter production and quality explain the large differences among species in the size of the forest floor C and N pools and in net N mineralization rates. The differences in the size and distribution of C and N pools beneath the different species suggest that the mechanisms regulating the process of species replacement in these forests will mediate the effects of anthropogenic, environmental changes in soil C and N dynamics.