Abstract
Seasonal changes in CO_2 concentration at different slope sites and different depths were investigated in stands of 42-year-old Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecypris obtusa) in Gunma Prefecture, 100 km northwest of Tokyo, Japan. The study sites were a lower cedar site (elevation ; 730 m), a middle cypress site (760 m) and an upper cypress site (800 m). Diffusion columns of 100 mL were placed in the soil at 5, 15, 25, 35 and 50 cm depths. CO_2 concentration in the diffusion columns was measured once or twice a month for 15 months with a CO_2 gas inspector. CO_2 concentration increased in the summer season and decrcased in the winter season. The range of CO_2 concentration in the soils was close to the atmosphere in shallow depths to 5600 mL at a depth of 50 cm. The relationships between CO_2concentration and soil temperature showed a high correlation coefficient. CO_2 concentration increased with depth at all sites. This reason was mainly attributed to the gas diffusion coefficient. In the case of deep soil, the CO_2 concentration for the lower site was higher than other sites and this tendency was clear in the sulmmer season. This might be attributed to the differences of source of CO_2 evolution. A higher CO_2 concentration was also observed in the winter at the lower site as compared to the other sites.
