1965 Volume 33 Issue 4 Pages 473-481
The influence of light intensity on photosynthetic rate of soybean plant population was studied with reference to light receiving aspect of the assimilation system. In this investigation, light condition was limited to the case where the intensity varies only by the change in weather condition. The case where horizontal light intensity varies with the variation in the angle of incidence, was eliminated to simplify the analysis of the problem. Light-photosynthesis relation was observed with the population as well as with single leaves. Light receiving aspect of the assimilation system was investigated by measuring the light intensity on the surface of the individual leaves under various light conditions. Then the photosynthetic response of the population to light intensity was analyzed on the basis of light-photosynthesis relation of single leaves and the light receiving pattern of the whole assimilation system. The results obtained are as follows; (1) The photosynthetic rate of single leaf increases rapidly with the increase in light intensity upto 15 Klx and then more slowly upto 25 Klx. Above this the photosynthetic rate is almost constant or rises only slightly. (2) Also in the photosynthesis of the population, light saturation was observed in general. (3) Under the condition in which the population is not so luxuriant and the spatial arrangement of the leaves is simple, light saturation is brought about by the saturation of individual leaves of whole assimilation system. Under full luxuriant condition, however, light saturation of population photosynthesis is not based on the saturation of individual leaves but on the mode of light receiving in the assimilation system, that is, any increase in the intensity of incident light beyond a certain limit will result only in a corresponding increase in the illumination of the already saturated upper leaves, while the unsaturated lower leaves remain practically unaffected.
