Greenhouse Gas Budget in a Larch Forest with Low Atmospheric N Deposition in Hokkaido, Northern Japan

Dissolved inorganic nitrogen (DIN) in throughfall, soil N2O and CH4 fluxes, soil organic matter decomposition (OMD), net primary production (NPP), tree N uptake and net nitrification potential were measured at each one site in five adjacent catchments with fairly identical soil type (Hapludants) and vegetation type (50 to 60 years old larch plantation) for 6 months during the non-snow cover period (June-November) for two years in Mt. Shirahata, Hokkaido, Japan. The net ecosystem production (NEP) was calculated as NPP-OMD and the global warming potential (GWP) was estimated from the negative of NEP, N2O and CH4 emissions using the IPCC recommendation. The throughfall DIN (kg N ha -1 6 months -1 ) ranged from 0.88 to 1.75 in 2003 and 0.91 to 1.79 in 2004, significantly lower than larch N uptake and nitrification potential. Methane was taken up by soil and N2O was emitted from it. Both CH4 uptake in and N2O emission from Mt. Shirahata were significantly lower than previously reported values, which is ascribed to low DIN deposition to this area. A positive GWP was obtained in this study mainly due to a negative NEP, indicating that the forests in Mt. Shirahata enhance global warming.