Acustom-built simple system for conditioning and measurement of in situ whole-cluster transpiration

A custom-built, low-cost gas exchange system designed for conditioning of the cluster microclimate and for fully automated measurements of in situ whole-cluster transpiration is presented. Measurements were carried out on potted Sangiovese grapevines at the onset of veraison. To increase the range of variability in cluster transpiration, air streams of different vapor pressure deficits (VPD) were created by conditioning the temperature of the incoming flow. Heating was created and maintained for 10 d (26 June - 5 July) by air flow through a metal segment equipped with three 75 W (warm) or 100 W (hot) light bulbs. The cluster transpiration rates recorded for the unheated (control) clusters throughout the conditioning period varied from 0.18 to 0.28 mmol m-2s-1. While the daily transpiration rates of clusters supplied with warm air were similar to those of the control, water loss began to decrease significantly in clusters treated with hot air from day 4 onward and stayed lower throughout the remaining conditioning period. The gas exchange system presented here proved sensitive enough to detect the typically low transpiration rates of berries during ripening; effects due to air heating could be separated from fluctuations caused by daily variation of weather.