群落構造

It is clear that a canopy architecture affects the CO_2 diffusion in a foliage. The CO_2 diffusion coefficient is expressed by D = U・i・l_m where D is diffusion coefficient, U is wind speed, i is relative turbulence intensity and I, is mixing length. In this paper we show the relation of canopy architecture with attenuation coefficient (β) of wind speed (U) in the canopy and drag coefficient (C_d) as one of the construction factors of β. The results are summarized as follows ; From the profiles of the wind speed above and within the canopies of barnyard millet, upland rice, paddy rice, wheat, soybean and short and tall types of grain sorghum, the attenuation coefficients (β) of wind speed and drag coefficients (C_d) of leaves in these canopies were obtained. The β obtained from the wind profile in the canopy can be expressed as β ∝ F_L・C_d where F_L is leaf area index. Though C_d of the horizontal foliage was smaller than that of vertical foliage, β of the soybean canopy was larger than paddy and upland rice vertical foliages compared on the same F_L. This resulted from the soybean canopy having large leaf area density (LAD) in upper layers of the foliage. The β of the tall type of grain sorghum was smaller than that of the short type. This resulted from the small C_d of the tall grain sorghum canopy. As mentioned above, it was found that the attenuation coefficient (β) of wind speed was affected by not only leaf inclination but also vertical distribution of leaf area and canopy height.