We conducted a field experiment in a cool‐temperate deciduous forest to investigate the dynamic behavior of soil CO2 and the vertical distribution of soil respiration. Soil CO2 concentration (C) was measured half‐hourly at four depths for 6 months in 2000 with infrared gas analyzers installed below ground. Using C profiles, soil surface CO2 efflux (F0), CO2 production rates of the topsoil (PA), and CO2 flux from the subsoil to topsoil (FCA) were evaluated half‐hourly by applying Fick's first law. Some remarkable short‐term and long‐term variations were found in C, F0, PA, FCA, and the contribution of topsoil respiration to total soil respiration (PA/F0), which include (1) rapid increase in C and decrease in F0 and PA due to rainwater infiltration, (2) diurnal variation in C coupled with that of the atmosphere, (3) diurnal variation in F0 and PA similar to that of topsoil temperature, (4) decrease in C, F0, and PA following soil drying in August, (5) linearly increasing FCA between late May and mid‐September, and (6) decrease in PA/F0 from around 0.9 during summer to 0.3 in November. The variation of PA was mainly controlled by soil temperature at −0.07 m between 7° and 17°C, although PA did not respond well to soil temperature above and below this temperature range. Above 17°C, PA increased linearly with soil moisture, and moisture variation accounted for the PA decrease in August. Neither temperature nor moisture explained the PA behavior below 7°C. Subsoil respiration (FCA) showed an exponential relationship with soil temperature at −1 m.

We collected leaf litter from a deciduous broadleaf forest and a larch forest in Hokkaido, Japan naturally without using litter traps or litter bags. The litter collection was conducted every month from October 2001 through October 2002 except in the snowy season. We measured the CO 2 production rate of the litter samples through microbial respiration using the chamber method in a laboratory under different temperature and moisture conditions to investigate the seasonal pattern and temperature and moisture responses of CO 2 production at the early stage of litter decomposition. Seasonal variation was found in the CO 2 production rate per unit of litter dry weight (P dw ), or the litter decomposition rate, for both broadleaf and larch litters. Although seasonal patterns differed somewhat according to temperatures and species, P dw reached the minimum in June. The moisture sensitivity of P dw decreased with time and reached the minimum in summer for both broadleaf and larch litters, whereas the seasonal pattern of the temperature sensitivity (Q 10 ) was not clear. The seasonal pattern of P dw was explained by its C: N ratio for broadleaf litter. For larch litter, however, the relationship between P dw and the C:N ratio was complicated because of fresh litterfall supplied gradually before defoliation. The temperature and moisture sensitivities of P dw changed in parallel with the C:N ratio for both broadleaf and larch litters, respectively. These facts suggest the importance of litter chemical quality in the early decomposition process of fresh litter and the validity of the C:N ratio as an index of litter quality.