Carbon and nitrogen changes in A_0 horizons in a Pinus densiflora forest established on a Mt. Fuji lava flow

Abstract

As part of a study on soil nitrogen (N) dynamics in Pinus densiflora Sieb. et Zucc. forests established on substrata in the early stages of primary succession, we studied seasonal changes in carbon (C) and N concentrations in A_0 horizon and C and N inputs by litterfall and dead fine roots in a mature P. densiflora forest established on a immature substrata on Mt. Fuji lava flow. The litter and coarse humus particles showed reductions in N concentration when belowground temperature increased despite their high C/N ratios (72-131 in the litter; 35-53 in the coarse humus particles). C/N ratios in the litter increased when the N concentration decreased. The increase in C/N ratios were not caused by the input of detritus with high C/N ratios in summer. Because some ectomycorrhizal fungi distribute in the research forest can use N in litter, we presumed that the increase in the C/N ratio from spring to summer when the pine tree grow vigorously, may be caused from the use of N in litter by the pine trees under the symbiosis with the ectomycorrhizal fungi.