Abstract
In order to analyze the interference of uncontrolled factors of environment with the temperature effect on plant growth and other plant responses, the effect of soil temperature on the hypocotyl elongation of cucumber seedlings was analyzed at respective air temperatures in the growth cabinet. The soil temperature was controlled 5°C higher and 5°C lower than respective air temperatures of 15, 20, 25, 30 and 35°C, and also controlled at the same temperatures as the respective air temperatures, with the use of the water bath system. Cucumber seeds were sown in the stainless pots filled with burnt chaff, and one day after germination, the seedlings were cultured under respective soil temperatures.
At air temperatures of 20 and 25°C, the hypocotyl elongations were promoted under higher temperature of soil, but inhibited under lower temperature of soil. At air temperature of 35°C, the hypocotyl elongation was promoted under lower temperature of soil, but inhibited under higher temperature of soil. The differences among the hypocotyl elonga-tions under respective soil temperatures were not significant at air temperatures of 15°C and 30°C.
In the phytotron glass rooms, the soil temperature was greatly affected by solar irradi-ation, and the maximum temperature of soil became 33.8°C even under air temperature of 25°C. Under this condition of the glass room, appreciable differences were found be-tween the respective hypocotyl elongations under the soil temperatures controlled and uncontrolled.
From these results, it is clear that the soil temperature remarkably interferes with the temperature effects on the hypocotyl elongation. This fact indicates that the control of soil temperature is necessary for the adequate analyses of the temperature effects on the plant growth and other plant responses.
