The effect of root-zone temperature on temperature difference between leaf and air in tomato plants

The temperature relationship among leaf, air and root zone was investigated in this study. Tomato, one of the main greenhouse crops, was used as the experimental material, and a nutrient solution recycling system was employed to grow the plants. Root-zone temperature was controlled at 23 +/- 1, 28 +/- 1 and 33 +/- 1 degrees C during the day between 10:00 and 17:00 for about 40 days. The results showed that, when root-zone temperature (T-rout) was around 23 degrees C, the temperature difference between leaf and air (Tl-a) was negative and was around-3-0 degrees C when air temperature (lair) was below 32 degrees C; when Tr..t was around 28 degrees C or higher, the difference was positive 70% of the time for Tl-a when Tair was lower than or equal to T.t; the highest Tl-a was 5 degrees C. For all treatments, the temperature difference between the leaf and air increased rapidly when Tair was higher than 32 degrees C. The Tl-a was-7 degrees C or more negative when Tair was up to 40 degrees C. A larger negative value of Tl-a means higher transpiration and higher energy consumption. A positive value of Tl-a indicates that water absorption was reduced or that the plants were water stressed. It was concluded that an air temperature higher than 32 C was not suitable for tomato growth. Tomato plants are in drought stress 70% of the time when the root-zone temperature was 28 degrees C or higher. It is suggested to decrease the root-zone temperature to around 23 degrees C during summer for growing tomato plants.