Nitrogen fixation associated with the leaf litter of Japanese cedar (Cryptomeria japonica) of various decomposition stages

Leaf litter and organic layer samples from Japanese cedar (Cryptomeria japonica) forests with varying decomposition stages were tested for nitrogen-fixing (acetylene-reducing) activities. The result obtained with samples from Gifu University Forest in Kuraiyama indicated that nitrogen-fixing activity was found almost exclusively at a certain limited stage of decomposition, possibly a fairly early stage termed F1 fraction. Specific activity for acetylene reduction by the fraction was 11.0 nmols acetylene reduced/g dry matter/hr. The maximum activity was obtained under 10% oxygen in the atmosphere, and this activity was 1.5 times higher than in 20% oxygen concentration. Nitrogen-fixing activity was measured of the litter and organic layer samples from several locations of Brown Forest Soil of various soil types under Japanese cedar forests. Again, the activity was found generally in F1 fraction. The F1 fraction was characterized by higher moisture content and pH, higher rate of carbon dioxide evolution, and little activity for nitrogen mineralization relative to the other decomposition stages. Result of the proximate analysis supported the assumption that F1 is fairly an early stage of decomposition, where organic solvent-extractable materials are much reduced from the leaf litter.