Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : XC. On the relation between the plant type of rice plant community and the light-curve of carbon assimilation

Abstract

Dividing a rice plant community, which had 7.1 leaf area index with straight and errect leaves, into two communities, one was a plant community with straight and errect leaves which was not treated at all and the other was a plant community with curved and drooped leaves which was made artificially by putting a small weight on the tip of every leaf of the plant community, the author & examined the relation of the rate of carbon assimilation to light intensity on the two plant communities. 1) In the plant commuity with straight and errect leaves the rate of carbon assimilation increased with light intensity and no light saturation point seemed to be found, while in the plant community with the curved and drooped leaves the rate of carbon assimilation increased with light intensity up to about 0.6 cal/cm2. min., but did not increase at all in higher light intensities than 0.6 cal/cm2. min. which seemed to be a light saturation point (Fig. 1-2). 2) As a result of comparing the structures of the two plant communities with each other after Monshi et Saeki, it was made clear that in the plant communities with straight and errect leaves all the leaves are near equally distributed in vertical direction and the sunlight seemed to penetrate fairly well to leaves in the lower layer, while in the plant community with curved and drooped leaves the leaves mostly distributed on the upper layer and the sunlight hardly penetrated in to lower leaves (Fig. 3). 3) For clarifying the reason why the light-curve of carbon assimilation changed with the change of plant type of the communities, an investigation was made on the light-receiving degree of all individual leaves in the two plant communities. The results suggested that in the community with straight and errect leaves the light-receiving degree increased with an increase of the sunlight intensity on most leaves synchronously and progressively, and consequently no light saturation point was found on its light-curve of carbon assimilation, while in the community with curved and drooped leaves the light receiving degree increased with an increase of the sunlight intensity only on a small number of leaves in the uppermost layer of the community and it attained more than a saturation light intensity, but it hardly increased on most leaves with an increease of the sunlight intensity, and consequently a light saturation point was found on the light-curve of carbon assimilation (Fig. 4). 4) The plant community with curved and drooped leaves was less by 34 % in the incresed weight of drymatter in the period after heading and also was less by 33 % in grain yield than that of the plant community with straight and errect leaves, respectively. 5) From the above mentioned facts it was concluded that the rice plant community with straight and errect leaves was one of the most necessary characteristics for maximizing the yield of rice.