Studies on the plant temperature

Abstract

The author carried out the observations of the diurnal variation of plant temperatures of grapes and egg plant, temperature of sweet potato and stem temperature of paddy rice from August to October in 1952 and also fluctuation of stem temperature of barley in March, 1956.The temperature of each plant were measured with copper-constantan thermocouples (diameter is about 0.15-0.2mm) being recorded by a potentiometer and galvanometer in 1952 and oscillo-graph in 1956. A junction was inserted in fruits, sweet potato and stem. The date, plants, weathers and instruments of measurement are shown in Tab. 1.The results obtained are as follows;(1) The diurnal change of sweet potato temperature compared with soil temperature near the soil surface is shown in Fig. 1 (A). In the day time, it is shown that soil temperature is the highest and temperature of central part of sweet potato is the lowest, and the reverse is shown in thenight. But differences of temperature between soil and sweet potato are small of about 1°C in the daytime and 0.1-0.2°C in the night.(2) The change with time of stem temperature of paddy rice after the pouring of cold and hot water is shown in Fig. 1 (B) and (C). It is recognized that differences of temperature between water and stem vanish within 3-4 minutes.(3) Diurnal change of temperature of egg plant fruits compared with air temperature is shown in Fig. 2 (A) and Tab. 2. In the daytime, it is recognized that the temperatures of the surface and of the central part of fruits are higher than air temperature with differences of 10°C and 5.5°C, respectively.There seems to be no doubt that this higher temperature is dependent on the solar radiation.(4) Diurnal change of temperature of grape fruits compared with air temperature is shown in Fig. 2 (B) and Tab. 2. It is shown that in the daytime temperature of grapes shined by the direct solar radiation is very higher than air temperature with differnces of about 5.4°C. But in the night, temperature of the grape is cooler than air temperature, and it seems that this cooling is dependent on nocturnal long wave radiation from fruit surface. However, temperature of fruits covered with leaves and stems is nearly equal to air temperature, and this is due to the protection of solar and nocturnal radiation.(5) Stem temperature of barley and air temperature at about 5cm high from the soil surface were recorded by the oscillo-graph, and then, Eulerian correlation coefficient (R(t)T) and spectrum were calculated from 180sec. recording as shown in Fig. 3 and Fig. 4, respectively. The Eulerian correlation coefficient curve is shown to fit the relation1-R(t)T∞t4/3within the range of small lag and this coincieds with theoretical result by Inoue. From Fig. 4, it is recognized that w(λ) of stem temperature vanishes at large λ, but w(λ) of air temperature does not.