Effects of environmental factors on leaf temperature in a temperature controlled room III. Difference in leaf temperature between adaxial and abaxial surfaces in cotyledon of Cucurbita maxima Duch.

Abstract

Leaf temperature was measured under various conditions of air temperature, relative humidity and light with the use of a micro-thermister, which was inserted into the cotyledon of Cucurbita maxima seedling.Under the condition of 70% relative humidity in darkness, the leaf temperature was lower than the air temperature at air temperatures of 20°C, 30°C, 40°C, but at the air temperature of 10°C, there was no difference between the leaf temperature and the air temperature. The difference between the leaf temperature and the air temperature was larger at higher temperatures.When the leaf was illuminated by a tungsten lamp with the intensity of 22 mW/cm2, the leaf temperature was higher than the air temperature at air temperatures of 10°C, 20°C, 30°C. The difference between the leaf temperature and the air temperature was smaller at higher temperatures. When the air temperature was changed from 30°C to 40°C under the illuminating condition, the leaf temperature once became 40.5°C and fell to 38.5°C and gradually converged to 39°C.When the relative humidity was changed from 80% to 40% at the air temperature of 40°C under illuminating conditions, the leaf temperature fell from 39°C to 35.5°C and gradually converged to 36.0°C. When the relative humidity was changed from 80% to 40% at the air temperature of 30°C under the same conditions, the leaf temperature fell from 34°C to 32.5°C. Thus, the effect of relative humidity on the leaf temperature was larger at higher temperatures and was scarcely observed at the air temperature of 20°C.From these results, it could be estimated that the leaf temperature was remarkably affected by air temperature, light, relative humidity, and their combinations.