Transpiration and energy balance of a greenhouse rose crop in mediterranean summer conditions

Abstract

The transpiration rate of a soilless rose crop and its interactions with the greenhouse microclimate and energy balance were investigated during summer conditions in Greece. At this aim, measurements of transpiration (γE c), canopy net radiation (Rn), air and canopy temperature (Ti and Tc, respectively), and air vapour pressure deficit (VPDi) were carried out during June and July 1998 in a white-washed glasshouse equipped with fan assistant ventilation. The sensible heat flux of the canopy (Hc) was deduced from the data of γEc and Rn. The results indicated that, although high air VPD were prevailing in the greenhouse (until 5 kPa), the transpiration rate was maintained rather high throughout the day at a level equivalent to double the net radiation. Canopy temperature was found significantly lower than air temperature during most of the day. The canopy conductance to water vapour transfer (gc) was estimated from the direct relationship linking transpiration to canopy-to-air VPD. The maximum values of gc were observed in the early morning, near 10 a.m. Afterwards, gc decreased and, during the afternoon, was found rather constant. Calculation of the crop water stress index (CWSI) indicated that, despite the high VPD, radiation and air temperature, the crop was only slightly stressed, the CWSI being not higher than 0.30 during this period. It was concluded that the crop was able to maintain a high physiological activity throughout the day. The ability of the crop to respond to the high evaporative demand created by the environmental conditions may be ascribed to the high crop LAI (about 4), roof whitening and adequate water supply, probably associated to a well-developed root system.