水稲群落の葉群の構造と直達光の透入について

抄録

Biometrical measurements were made to make clear the change in geometrical structure of rice canopy during the growing season. The results were used to clarify the penetration of direct sun-light into the canopy. The penetration of direct sun-light was calculated from Eq. (1) proposed by Ross and Nilson (1965). The geometrical characteristics of the canopy was found to be a vertical foliage-type at about the heading stage and to change the more horizontal one at about the waxy stage of ripening. The effective leaf area function (G_L (w)) that denotes cosine of the angle between leaf normal and sun direction was determined at each layer within the canopy. The special mean (G^^-_L) of the effective leaf area function was also determined by considering the vertical distribution of leaf area density (f_L(z)) and the effective leaf area function (G_L(w)). Both of G_L(w) and G^^-_L were found to change remarkably with the sun altitude (h₀), showing that the types of change are dependent upon the growth stages of rice crops. The ratio (F_d/F_t) between the partial leaf area index of sun-lit foliage (F_d) and the whole leaf area index (F_t), the ratio (_abF_d/F_d) between the partial leaf area index of foliages receiving light on the reverse side (_abFd) and the sun-lit leaf aera index (F_d), and the extinction coefficient of direct sun-light (k_d) changed by the sun altitude (h₀). The forms of change in these three parameters all depend upon the geometrical characteristics of canopy. It has been pointed out that the vertical foliage-type community is favorable for the photosynthetic activity since the direct sun-light can penetrate into the deeper layer, and that the horizontal foliage-type community is less favorable since the direct sun-light is apt to be absorbed at the upper layers and cannot penetrate into the community so deeply.