Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : CII. Relations between the leafiness of rice plant Communities and their light-curves of carbon assimilation

[摘要] On the basis of the experimental results, Matsushima, one of the authors, has hitherto had an opinion that the light saturation point is always found on the light-curves of carbon assimilation in rice plant communities regardless of their leafiness, and he has been in opposition to Takeda et al (1955, 1956, 1957, 1957), Murata (1961), Shimizu and Tsuno (1956) and others who have reported that the light saturation point is found only in rice plant communities with a low leaf-area-index and that it goes up with an increasing leaf-area-index and it disappears in communities with a high leaf-area-ihdex and finally in an extremely leafy communities the light-curve of carbon assimilation gets near to a straight line. Using various rice plant communities differing in leafiness, the authors have re-examined the relation between the leafiness of communities and the light-curves of carbon assimilation since 1963. Different results have been obtained in the present experiments from those in the author's past experiments. The reason why the light-curves of carbon assimilation in rice plant communities are affected by their leafiness was considered to be ascribed to the changes in receiving the amount of light on each leaf in plant communities due to their different leafiness, but the authors were impossible to prove the point because of the difficulty in measuring the amount of light on each leaf in nursery beds. Therefore, using adult plant communities in paddy fields, the authors examined the relation between the leafiness of plant communities and the light-curves of carbon assimilation and further studied the above mentioned reason according to Kumura's method. The results can be summerized as follows. 1) From the investigation on the diurnal changes of the rate of carbon assimilation in rice seedling communites differing in spacing (8×8 cm, 4×4 cm, 2×2 cm and 1×1 cm) from 4 th to 12 th leaf-stage during 3 seasons, almost identical results among 3 seasons have been obtained, i. e. a light saturation point is clearly recognized in communities with a low leaf-area-index and it goes up with an increasing leaf-area-index and finally it disappears in communities with a high leaf-area-index, as can be seen in Fig. 1. 2) In the previous experiments (1), however, the amount of nitrogen absorbed per plant differs with one another in different spacing plots, and consequently the rate of carbon assimilation per unit leaf-area as well as the plant type of seedlings are also different with different spacing plots, which may affect the light-curves of carbon assimilation. In the second experiments, therefore, a plant community has been thinned out uniformly in different rates just before the measurements so that the community may be divided into 4 different leafy communities and each community may have an equal rate of carbon assimilation per unit leafarea and an equal plant type with one another, and the measurements have been conducted on each different spacing plot thus treated. The results are nearly indentical with those of previous experiments, as can be seen in Fig. 2. 3) In general, in case of the measurements of diurnal changes in the rate of carbon assimilation under natural conditions, high light intensities appear at the time when the sun altitude is high and low light intensities are liable to appear when the sun altitude is low, so the light-curves of carbon assimilation in plant communities obtained from the diurnal changes of sunlight are affected by not only the sun altitude but also the percentage of the amount of diffused light to the totoal amount of sunlight. In the third experiments, therefore measurements have been conducted under a definite sun altitude and under different light intensities obtained through different thiknesses of aventurine vinyl films which make the sun light completely diffuse. The results obtained are also nearly identical with those of Fig. [the rest omitted]

[学科分类] 农业科学（综合）