Seasonal changes in the contribution of root respiration to total soil respiration in a cool-temperate deciduous forest

A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (R_trench) and in a control plot (R_control) were measured from May 2000 to September 2001 by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (R_D) was estimated by using a root-bag method to correct the soil respiration measured from the trenched plots for the additional decaying root biomass. The soil respiration rates in the control plot increased from May (240–320 mg CO₂ m^–2 h^–1) to August (840–1150 mg CO₂ m^–2 h^–1) and then decreased during autumn (200–650 mg CO₂ m^–2 h^–1). The soil respiration rates in the trenched plot showed a similar pattern of seasonal change, but the rates were lower than in the control plot except during the 2 months following the trenching. Root respiration rate (R_r) and heterotrophic respiration rate (R_h) were estimated from R_control, R_trench, and R_D. We estimated that the contribution of R_r to total soil respiration in the growing season ranged from 27 to 71%. There was a significant relationship between R_h and soil temperature, whereas R_r had no significant correlation with soil temperature. The results suggest that the factors controlling the seasonal change of respiration differ between the two components of soil respiration, R_r and R_h.