Influence of misting on the diurnal hysteresis of canopy transpiration rate and conductance in a rose greenhouse

Abstract

The aim of this study was to evaluate the effects of greenhouse air humidity control on the transpiration rate (TR) and canopy stomatal conductance (gc) of a soilless rose crop (Rosa hybrida, cv. First Red) grown on perlite bags. Measurements of TR, canopy net radiation (Rn), air (Ta) and canopy (Tc) temperature, and air vapour pressure deficit (VPDa) were made in a glasshouse located in the coastal area of eastern Greece during several summer days. The greenhouse was operated (i) without air humidity control and (ii) with control by means of a fog-system operating when the relative humidity of the glasshouse air was lower than 75%. The diurnal course of gc was determined from the relation linking TR to canopy-to-air vapour pressure deficit (VPDC) or from inversion of the Penman-Monteith equation. The two ways of estimating gc were in agreement. Diurnal hysteresis of TR and gc in relation to VPD C were observed and showed different patterns according to changes in the daily amplitudes of VPDC induced by the humidity control system. The hysteresis phenomena were less strong when the fog-system was operating. The changes in the daily course of TR and gc were probably due to the stomatal response to vapour pressure deficit. Thus the prediction of short-term variations of TR and gc in greenhouse environments must account for the magnitude and time-course of VPDC.