Soil respiration (SR) can be divided into heterotrophic (HR) and root respiration (RR). Recent studies suggest that they show diurnal variations and factors controlling the variations would differ among SR, HR and RR. However, there is little information about diurnal variation of SR, HR and RR in natural forest ecosystems which have complex forest structure and seasonality. We aim to clarify the diurnal variations in SR, HR and RR by a continuous measurement in a forest ecosystem.

This study was conducted in a cool-temperate deciduous forest in Japan. We measured continuously CO₂ flux from the soil surface in control (with root) and trenched (without root) plots by closed chamber method with automatic open/close chamber. The CO₂ flux from control and trenched plots were regarded as SR and HR, respectively, and RR was calculated as the difference between SR and RR.

All of SR, HR and RR showed clear diurnal variations in all seasons. HR correlated with soil temperature measured in some hours before the flux measurement, although RR didn’t show clear correlations with soil temperature in a single day. The pattern of diurnal variations in HR shifted among the season, whereas clear seasonal trend was not recognized for that in RR. Moreover, we will discuss the differences in diurnal and seasonal variations between HR and RR in relation to some environmental factors.