Set-up, calibration and testing of a custom-built system for measuring whole-canopy transpiration in grapevine

Upgrading of a whole-vine gas exchange system able to take automated measur ements of canopy water loss under close-to-ambient conditions is reported. Vine canopies are enclosed in clear, inflated polyethylene chambers fed wit h ambient air at a flow speed suitable to limit chamber overheating within 2-3 degrees C. Water loss is calculated from the air flow and the inlet-out let water vapor differential computed from dry and wet bulb temperatures. C alibration of canopy water loss estimated by the system at various flow rat es vs. actual gravimetric water loss recorded for a vine canopy of about 15 m(2) of leaf area resulted in a close linear relationship (R-2 = 0.93), al though the air flow had to be adjusted above 40 Ws to assure a temperature increase inside the chamber no higher than 3.1 degrees C. Data examples the system can deliver are also reported with emphasis on the variations in th e diurnal trend of whole-canopy transpiration (WCE) as affected by differen t canopy shapes and orientations. The system was sensitive enough to detect a temporary decrease of WCE in the mid-day hours when measurements were ta ken on NS-oriented vertical hedgerow canopies as compared to canopies eithe r EW-oriented or arranged to resemble the spherical shape of the goblet tre llis. Its simplicity, ease of set up, transportability and low cost make th e system a valuable tool to assess water loss at the grapevine canopy level . Automation also allows different treatments to be compared in the long ru n and the flexible plastic enclosure enables measurements to be run on cano pies widely differing in shape and size.