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.