Proces Identification and Optimal Control of Plant Growth (IX)

Relationship between Leaf Temperature and Photosynthesis

Abstract

In previous papers, it was made clear that transpiration and stomatal aperture can be estimated by monitoring leaf temperature under controlled environments. Since the photosynthetic rate is closely related with transpiration and stomatal aperture, whether it is possible to determine the photosynthetic rate by monitoring leaf temperature under the controlled environment was examined.
The results of the experiments are as follows. When the light was switched on, leaf temperature and photosynthetic rate increased and after leaf temperature reached its maximum point it decreased though the photosynthetic rate continued to increase. Up to the maximum point of leaf temperature, the photosynthetic rate was closely related with the increase of leaf temperature. On the other hand, after the maximum point of leaf temperature was reached, the photosynthetic rate rose relevant to the decrease of leaf temperature. This relationship was not observed before 12 min after light-on. When either a weak or strong water stress was forced onto the root of the plant by turning the water culture supply on and off, leaf temperature and the photosynthetic rate began to oscillate in an inversely corresponding relation.
The relationship between photosynthetic rate and leaf temperature was investigated and partly elucidated. Computer control can be performed easily if the characteristics mentioned above are memorized by the computer and optimal manipulation of environment is selected by processing of the monitored leaf temperature.