Carbon dioxide efflux from the floor of a boreal aspen forest. II. Evaluation of methods — verification by infra-red analysis of a dynamic closed chamber

Concern over the global exchange of carbon has highlighted the need for reliable estimates of soil CO 2 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 tremuloides) forest. The three methods were: (1) soil CO 2 concentration gradients 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 temperature and nighttime eddy correlation measures of CO 2 fluxes above the forest understory (4 m) and overstorey (39 m). We found reasonable agreement between DCC-IRGA and method 1a (R 2 = 0.44 to 0.62), and excellent agreement between DCC-IRGA and the other methods (1b, 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 discussed. Key words: CO 2 flux, soil respiration, soil CO 2 concentration, eddy correlation