An improved multichamber gas exchange system for determining whole-canopy water-use efficiency in grapevine

A multichamber whole-canopy gas exchange system coupled with an automatic pot weighing device was tested for continuous 24 hr recording over 50 days in a trial comparing cv. Sangiovese vines subjected to progressive reduction of total transpiration water supply to well-watered vines. The system ran smoothly under regular maintenance for the entire period and gravimetric vine water loss was highly correlated with chamber-derived vine transpiration (r = 0.95) for data pooled over treatments. Seasonal and diurnal whole-canopy net CO2 exchange rate (NCER) and transpiration (Tc) showed that supplying 50% and 30% of daily gravimetric vine water loss (Tg) consistently corresponded to a NCER more than proportionally limited as compared to Tc, hence leading to lower canopy water-use efficiency (WUE) expressed as NCER/Tc ratio. Conversely, canopy WUE did not differ between treatments at 70% Tg restitution and rewatering. Similarly, during the most limiting water supply periods, the WUE difference between treatments was greatly reduced during cloudy days with lower vapor pressure deficit and higher diffuse-to-direct light intensity ratio. Data sets taken over different time frames on whole-canopy WUE provide a scenario different from that which might derive from traditional single-leaf assessment, reporting in almost all cases that intrinsic WUE increases under stress and suggests that the methodology used can mask or alter conclusions about adaptive response of grapevine cultivars to water stress. © 2014 by the American Society for Enology and Viticulture. All rights reserved.