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

Abstract

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.