Thermal Regime of Grapevines

Abstract

Leaf and berry temperatures, cluster water loss, and stomatal resistances of <i>Vitis vinifera</i> L. grape-vines 9Carignane9, 9Muscat of Alexandria9, and 9Torontel9 were determined. The temperature of exposed fruits were 1.4 to 7.3°C higher than air temperatures and shaded berries were 0.5 to 4.4°C lower than air temperatures between 8:00 a.m. and 6:00 p.m. The maximum temperature differential across the berry at a given time was 10.7°C. The increase in berry temperature above air temperature was the result of low transpirational cooling. The latent heat flux density and the change in heat storage terms were only a small fraction of the total energy balance of the grape berry, and most of the absorbed energy went into sensible heat. Leaf temperatures were very close to air temperatures. Transpirational cooling in leaves is very efficient as a result of low stomatal resistances at times of high energy load. The abaxial stomatal resistances decreased with increasing leaf temperature.