Transpiration flow rate in a full-grown tree ofPrunus avium L. estimated by the method of heat balance in connection with some meteorological factors

The course of the transpiration flow rate (Q_w), of transpiration flow acceleration (Q_w/dt) and of the integrated transpiration flow was determined during an average summer day by repeated measurements according to the method of heat balance and the free water capacity of the tree trunk was estimated. The relations between the transpiration flow rate and the temperature and relative humidity of the air and the vapour pressure deficit measured at the same time in their diurnal course, as well as at the single diurnal terms during the whole time at which measurements were carried out were determined by correlation analysis. The problems linked with the effect of various meteorological conditions during different times of the day, of rain showers, solar radiation and soil water content are discussed. The possibilities of explaining the midday depression of transpiration on the basis of repeated measurements of the transpiration flow rate are evaluated.