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

TLDR

Global carbon exchange concerns demand reliable soil CO₂ efflux estimates. The study aims to identify suitable methods for estimating soil CO₂ efflux. Using a dynamic closed chamber with an infrared gas analyzer, the authors compared three alternative approaches—diffusion theory, an empirical relationship, a steady‑state chamber, and temperature‑based daytime estimates—to assess soil CO₂ flux. The DCC‑IRGA results aligned reasonably with diffusion theory and excellently with the empirical, steady‑state, and temperature‑based methods, indicating all approaches are viable. Keywords: CO₂ flux, soil respiration, soil CO₂ concentration, eddy correlation.

Abstract

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