A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (Rtrench) and in a control plot (Rcontroi) were measured from May 2000 to September 2001by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (Ro) 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 C02 m-2 h-1 ) to August (840-1150 mg C02 m-2 h-i ) and then decreased during autumn (200-650 mg C02 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 (Rr) and heterotrophic respiration rate (Rh) were estimated from Rcontrol, Rtrench, and Ro. We estimated that the contribution of Rr to total soil respiration in the growing season ranged from 27 to 71 %. There was a significant relationship between Rh and soil temperature, whereas Rr 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, Rr and Rh.Abbreviations: Ro -carbon emission due to the decomposition of residual roots; Rh -heterotrophic respiration rate; Rr -root respiration rate; NEP -net ecosystem production; NPP -net primary productivity

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