Long‐term half‐hourly measurement of soil CO₂ concentration and soil respiration in a temperate deciduous forest

We conducted a field experiment in a cool‐temperate deciduous forest to investigate the dynamic behavior of soil CO 2 and the vertical distribution of soil respiration. Soil CO 2 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 CO 2 efflux ( F 0 ), CO 2 production rates of the topsoil ( P A ), and CO 2 flux from the subsoil to topsoil ( F CA ) were evaluated half‐hourly by applying Fick's first law. Some remarkable short‐term and long‐term variations were found in C , F 0 , P A , F CA , and the contribution of topsoil respiration to total soil respiration ( P A / F 0 ), which include (1) rapid increase in C and decrease in F 0 and P A due to rainwater infiltration, (2) diurnal variation in C coupled with that of the atmosphere, (3) diurnal variation in F 0 and P A similar to that of topsoil temperature, (4) decrease in C , F 0 , and P A following soil drying in August, (5) linearly increasing F CA between late May and mid‐September, and (6) decrease in P A / F 0 from around 0.9 during summer to 0.3 in November. The variation of P A was mainly controlled by soil temperature at −0.07 m between 7° and 17°C, although P A did not respond well to soil temperature above and below this temperature range. Above 17°C, P A increased linearly with soil moisture, and moisture variation accounted for the P A decrease in August. Neither temperature nor moisture explained the P A behavior below 7°C. Subsoil respiration ( F CA ) showed an exponential relationship with soil temperature at −1 m.