Aiming to clarify the mechanism and prediction of CO
2 exchange between a plant community and the atmosphere, a multilayer model of CO
2 exchange having a feedback function is proposed. This model can calculate not only the profile of CO
2 flux within and above a canopy, but also the profile of meteorological elements such as solar radiation, long-wave radiation, air temperature, specific humidity, wind velocity and CO
2 concentration. The profiles are calculated using information on the canopy structure, leaf characteristics, and meteorological elements observed over the plant community. In order to validate the reproducibility of CO
2 flux over the plant community by this model, we observed CO
2, latent heat and sensible heat flux over aplanted forest, albedo and the profile of relative wind velocity, downward diffuse solar radiation and CO
2 concentration within the canopy. By applying this model, we found that it could successfully reproduce not only CO
2 flux, but also latent heat and sensible heat flux, over the canopy and reproduce the profile of these meteorological elements. Moreover, numerical experiments on CO
2 flux were carried out using this model to investigate the influence of the characteristics of canopy structure on CO
2 flux. As a result, we found the followings: (1) When the values of LAI arc 6 and 8, the fluctuations of CO
2 fluxes over a canopy are more sensitive to the meteorological elements over the canopy than when the values are 1 and 3. (2) CO
2 absorption by a community is not always greater during high solar elevation, as the average value of leaf inclination is greater. (3) Among the three canopies studied in the numerical experiments, one whose distribution of leaf area density is almost even absorbs CO
2 gas the most.
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