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 (RD) 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 CO ₂ m^-2 h^-1) to August (840-1150 mg CO _-2 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.