落葉広葉樹林土壌からのCO_2フラックスの日変化と植生に対するCO_2供給源としての重要性

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In order to clarify the daily changes of CO_2 efflux from the soil of a deciduous broad-leaved forest, the CO_2 concentration profile from soil to atmosphere was measured at Tomakomai Experimental Forest of Hokkaido University in early September of 1990. The soil of this forest is classified as a volcanogenous regosol derived from Tarumae-a and b. The CO_2 efflux was determined by the gas diffusion law, using the values of the CO_2 concentration gradient at the surface of the H/A horizon as well as the gas diffusion coefficient measured independently. The CO_2 production rate of the H/A horizon was estimated by using the mass balance equation. The respiration of plant roots in the H/A horizon was estimated by subtracting the respiration rates of microbes and earthworms which were independently measured by the flask incubation method, while assuming that the cutted-roots respiration rate in the flask was relatively low. The CO_2 efflux showed a tendency for periodic change : decrease in the daytime and increase in the night, ranging from 1.55 to 3.18 × 10^<-4> g m^<-2> s^<-1>. The CO_2 production rate of the H/A horizon showed a similar tendency. On the contrary, the CO_2 production rate of microbes and earthworms in the H/A horizon did not show remarkable daily changes, therefore, the respiration of plant roots in the H/A horizon was considered to have a great influence on the daily changes of soil respiration. The averaged CO_2 efflux during this observation was 2.13 × 10^<-4> g m^<-2> s^<-1>, 61% of which was supplied by three CO_2 producers (microbes, earthworms and plant roots) in the H/A horizon ; each contribution was estimated to be 15, 3 and 43%, respectively. Assuming that CO_2 fixation by forest vegetation occurs when the minimum atmospheric CO_2 concentration was observed in and below the forest canopy, 69% of the total CO_2 efflux from forest soil during this observation was estimated to be fixed by forest vegetation. These results suggest that the CO_2 efflux from deciduous broad-leaved forest soil contributes largely as a CO_2 source to the photosynthesis of forest vegetation, and the H/A horizon is significant as a productive CO_2 layer in this forest soil. Moreover, the respiration of plant roots was considered to have a great influence on the daily changes of respiration in the forest soil.
1997-04-05

落葉広葉樹林土壌からのCO_2フラックスの日変化と植生に対するCO_2供給源としての重要性

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