Circadian rhythms of dragon tree leaf temperature and the amount of dew falling on them

Comparison of circadian rhythms of plant leaf temperature and dew point makes it possible to identify time intervals of dew falls. Using the dragon tree (Dracaena draco L.) as an example, it was shown that under arid conditions a CAM plant is able to condense and absorb up to ½ liter of water from 1 m2 of leaf surface cooled below the dew point during the night. It is assumed that the decrease in leaf temperature is associated with the conjugated action of two factors, thermal radiation and transpiration cooling. During the experiments, data were obtained indicating the existence of a special period at the beginning of daylight hours, when the temperature of the leaf surface drops by 5-10°C below the dew point. The coincidence of the maximum air temperature and the minimum temperature of the leaves allows us to consider the evaporation of dew from the surface of the leaves as the most likely cause of the strong cooling of the leaves and the precipitation of a large amount of dew in the morning. Using the entire chilled leaf surface to condense atmospheric moisture and absorb the fallen dew with the help of stomata open at night and water-absorbing tissues in the axils of the leaves is a striking adaptation to the conditions of a lack of water resources, including morphological, anatomical and physiological adaptations.