CARBON-DIOXIDE EFFLUX FROM THE FLOOR OF A BOREAL ASPEN FOREST - II - EVALUATION OF METHODS - VERIFICATION BY INFRARED-ANALYSIS OF A DYNAMICCLOSED-CHAMBER

Concern over the global exchange of carbon has highlighted the need fo r reliable estimates of soil CO2 efflux (soil Fc). Appropriate methods to estimate soil Fc must be identified and adopted. In this study we used a dynamic closed chamber and infra-red gas analyzer (DCC-IRGA) to verify the use of three other methods in a boreal aspen (Populus trem uloides) forest. The three methods were: (1) soil CO2 concentration gr adients and volumetric soil moisture by both diffusion theory (a) and empirical relationship (b), (2) an automated steady-state chamber and (3) daytime estimates derived from a relationship between soil tempera ture and nighttime eddy correlation measures of CO2 fluxes above the f orest understory (4 m) and overstorey (39 m). We found reasonable agre ement between DCC-IRGA and method la(R-2 = 0.44 to 0.62), and excellen t agreement between DCC-IRGA and the other methods (Ib, R-2 = 0.76 to 0.88; 2, R-2 = 0.89 and 3, R-2 = 0.64 to 0.80). Each of these methods has advantages beyond the scope of the DCC-IRGA, and these are discuss ed.