Forest Litter Decomposition in Relation to Soil Nitrogen Dynamics and Litter Quality

Abstract

Decomposition and changes in nitrogen and organic—chemical content of six types of forest litter were studied for 2 yr in five adjacent Wisconsin forests. The five forests were floristically dissimilar, being dominated respectively by sugar maple (Acer saccharum), white oak (Quercus alba), bigtooth aspen (Populus grandidentata), white pine (Pinus strobus), and hemlock (Tsuga canadensis), Nitrogen mineralization rates in the five stands ranged from 29 to 125 kg°ha—1°yr—1. Decomposition rates of transplanted sugar maple leaves and red maple (Acer rubrum) wood were not correlated with nitrogen mineralization rates in all five stands, indicating that nitrogen mineralization rates do not affect initial decomposition rates. However, mineralization rates were correlated with decomposition rates of the native dominant foliage litter. Nitrogen first accumulated in all litters, but by the end of the 2—yr incubation period nitrogen release had begun in all foliage litters. Nitrogen concentrations increased approximately linearly with cumulative mass loss but eventually declined in some foliage litters. Neither maximum amount of nitrogen accumulated nor amount accumulated per gram of litter mass loss was related to the rate of soil nitrogen mineralization. Chemical composition of litter affected decomposition rates and patterns. Soluble substances and litters relatively rich in solubles disappeared rapidly during early stages of decomposition. Eventually, slowly disappearing acid—soluble and acid—insoluble substances dominated the pattern of mass loss in all litters.