Model of CO₂ flux between a plant community and the atmosphere, and simulation of CO₂ flux over a planted forest.

Abstract

Aiming to clarify the mechanism and prediction of CO₂ exchange between a plant community and the atmosphere, a multilayer model of CO₂ exchange having a feedback function is proposed. This model can calculate not only the profile of CO₂ 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 CO₂ 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 CO₂ flux over the plant community by this model, we observed CO₂, latent heat and sensible heat flux over aplanted forest, albedo and the profile of relative wind velocity, downward diffuse solar radiation and CO₂ concentration within the canopy. By applying this model, we found that it could successfully reproduce not only CO₂ flux, but also latent heat and sensible heat flux, over the canopy and reproduce the profile of these meteorological elements. Moreover, numerical experiments on CO₂ flux were carried out using this model to investigate the influence of the characteristics of canopy structure on CO₂ flux. As a result, we found the followings: (1) When the values of LAI arc 6 and 8, the fluctuations of CO₂ fluxes over a canopy are more sensitive to the meteorological elements over the canopy than when the values are 1 and 3. (2) CO₂ 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 CO₂ gas the most.