植物群落構造と光, 温度の関係について

抄録

In order to make clear the relationship between environmental conditions and structure of plant community, the time courses of the vertical variations of light and temperature were observed in artificial plant communities of Fagopyrum esculentum with three planting densities (400, 100 and 25 plants per 1m²) at the farm in Toridemachi, Ibaraki prefecture on 2nd-3rd and 16th-17th July 1955, in parallel with the analysis of the structure of those plant communities by “the stratifying clip method”.
Light factor: Relative light intensity was measured with two electric photocells under diffused light (e. g, immediately after sunset). The vertical distribution of light intensity was firstly dependent on the leaf density and the height of leaf layer of plant community, secondly on the inclination of leaves, which increased when leaves had wilted and closed their stomata under the stronger solar radiation and water deficiency.
Temperature factor: The daily changes of vertical distributions of air temperature within plant communities and in an open land were measured with a series of thermometers (10cm. long) shaded by thicker white papers, and that of earth temperature with a series of L-tube earth thermometers. The daily temperature courses observed in air and soil-layer were respectively shown as sine curves with the period of one day by means of harmonic analysis. The vertical thermal diffusibility was obtained from such calculation that the difference of amplitude between two heights was put into the solution of the differential equation of heat conduction. Regarding air temperature, with the increasing density of the plant organs, especially of leaves, at each height above the ground, the amplitude and the vertical thermal diffusibility became smaller and the phase later. However, the amplitnde and the phase seemed dependent not only on the leaf density at each height but also on the vertical distance from the upper surface of plant cover to that height.
In the plant community the upper surface of plant cover was heated by day and cooled by night, as well as the ground surface. The daily variation of heat quantity accumulating in plant Immunity by day and dispersing from it by night were expressed by sine curves, which were obtained by combining one sine curve showing the daily change of transporting heat through the upper surface of plant cover with the other sine curve showing that through the ground surface. Consequently, it was known that the daily change of such a heat quantity within the plant community was mainly dependent only on the leaf density in the upper surface of plant cover.
Temperature of leaf was measured with a thermocouple at its lower surface. The hot junction was made so sharp and the leading wire adjacent to the hot junction was so fine that the heat conduction from the leaf was considerably depressed. The temperature of leaf exposed to the sun light was 0.5-1.0°C higher than the surrounding air temperature under general wind velocity, but that of shaded leaf was about 1.0°C lower. In the night, however, the difference of temperature between the leaf and the surrounding air could be hardly recognized.