Few studies examined the stomatal conductance (gs) characteristics of grapevines with an emphasis on daily climatic responses. In the present study, diurnal measurements on leaf temperature and gs of three grapevine cultivars (Alphonse Lavallée, Crimson Seedless and Italia) were carried out. The leaf temperature values for the cultivars at 08:30 were 25.0 ±1°C and it increased to a maximum value between 12:00 and 14:50 p.m. After an almost steady course, it decreased along with the decrease in ambient temperature. The gs values increased from morning (08:30 a.m.) to mid-morning (10:30 a.m.) for all the cultivars. After reaching a peak level at mid-morning, the gs decreased gradually from the mid-morning throughout the afternoon. In the morning, the highest and the least gs values were obtained from Italia (232 mmol H₂O m^-2 s^-1) and Crimson Seedless (149.6 mmol H₂O m^-2 s^-1) cultivars. At around 10:30, the gs for Italia, Crimson Seedless and Alphonse Lavallée were at the highest levels with their valus 287.7, 262.1 and 242.0 mmol H₂O m^-2 s^-1, respectively. The last measurements on gs at around 16:10 varied from to 96.7 (Italia) to 112.0 mmol H₂O m^-2 s^-1 (Alphonse Lavallée). During the daily time course, the gs depended mainly on irradiance. T_leaf showed a strong relationship with T_air for all the cultivars. There was a strong, but negative correlation between leaf temperature and air humidity for all the cultivars.

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