Phytometrical Studies of Crop Canopies : IV. Structure of canopy photosynthesis of rice plants

[摘要] The data of the variation in radiation environment from leaf to leaf have been used in order to study the microstructure of canopy photosynthesis of rice plants. The gross photosynthesis Φ(i) of the whole leaf area of the layer i can be given by Φ(i)=ΣΔF(i)F(i, S)Φ(S), where ΔF is the partial leaf area of the layer i, F(i, S) the probability density function of the leaf area of the i-th layer which is radiated by a given value of irradiance S, and Φ(S) the irradiance-photosynthesis function of the leaf. Therefore, the gross photosynthesis Φt of the whole leaf area of the rice canopy is the sum of the Φ(i) as follows: Φt=Σ^^n__(i=1)Φ(i), where n is the total number of the canopy layers. The main results from the calculations made by using the data of the partition function of solar energy between the leaves can be summarized as follows: 1. The layer's mean of the gross photosynthesis of shaded leaves decreased with the leaf area depth, mainly because of attenuation of the intensity of diffuse radiation flux on leaf surfaces. The gross photosynthesis intensity of the shaded leaves in an upper layer goes up with increasing the total diffuse radiation flux IT which consists of sky diffuse radiation flux and complementary diffuse radiation fluxes (upward and downward) due to the scattering of radiation by plant elements. On the other hand, the layer's mean of the gross photosynthesis of the sunlit leaves was approximately constant reagardless of sun altitude and the canopy depth. The above results were compared with those obtained by Ross and Bikhele (1968, 69) in good agreement. 2. The contribution of leaves which are irradiated by a certain irradiance S=Q0(γo)|cos <γoγL>^^^^^|+IT to the gross photosynthesis of the layer i or the canopy was determined by Φ(S)=ΔF·F(S)Φ(s)/Φ. As can be seen in Figs. 2 and 3, when sun altitude is relatively low, the contribution function Φ(S) is characterized by three peaks at low (0∼0.2ly/min), medium (0.4∼0.6ly/min) and high (0.9∼1.1ly/min) irradiance intensities. The peak in low irradiance region is due mainly to the contribution of the shaded leaves and the peak in high irradiance range is because of the sunlit leaves with relatively small value of the angle between the sun's ray and the leaf normal. The characteristics of Φ(S) function as described here was more manifest for canopies with more erected leaves (Manryo, Aug. 25 : IR-8, Sept. 14) than for a canopy with somewhat lax leaves (Manryo, Sept. 14). With increasing sun altitude, the peak observed in the high irradiance range became gradually indistinct due chiefly to the decrease of the angle <γoγL>^^^^. When sun altitude is high, the function Φ(S) shows pronounced asymmetry, indicating the broader skirts in the higher irradiance range than in the lower irradiance range. 3. Fig. 4 shows the gross photosynthesis of sunlit leaves and shaded leaves is zero at the canopy top, increases with the depth, to reach its maximum and decreases again. Although the peak of gross photosynthesis was approximately the same between sunlit and shaded leaves when sun altitude was low, the peak intensity of gross photosynthesis of the sunlit leaves increased more rapidly with increasing sun altitude than the shaded leaves did. It was about two times as large as the peak intensity of the shaded leaves at the time of southing. The canopy level at which the gross photosynthesis of the sunlit leaves became maximal was higher than that of the shaded leaves. The canopy level with the maximal photosynthesis moved gradually downward with increasing sun altitude. Fig. [the rest omitted]

[学科分类] 农业科学（综合）