TY - JOUR T1 - An Improved MultiChamber Gas Exchange System for Determining Whole Canopy Water Use Efficiency in the Grapevine JF - American Journal of Enology and Viticulture JO - Am. J. Enol. Vitic. DO - 10.5344/ajev.2014.13117 SP - ajev.2014.13117 AU - Stefano Poni AU - Maria Clara Merli AU - Eugenio Magnanini AU - Marco Galbignani AU - Fabio Bernizzoni AU - Alberto Vercesi AU - Matteo Gatti Y1 - 2014/01/23 UR - http://www.ajevonline.org/content/early/2014/01/21/ajev.2014.13117.abstract N2 - A multi-chamber whole-canopy gas exchange system coupled with an automatic pot weighing device was tested for continuous 24-h recording over 50 days on a test trial comparing cv. Sangiovese vines subjected to progressive reduction of total transpiration water supply (WS) vs. well-watered vines (WW). 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) very consistently showed that supplying 50% and 30% of daily gravimetric vine water loss (Tg) always corresponded to a NCER being 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 re-watering. Similarly, during the most limiting water supply periods, the WUE difference between treatments was greatly reduced during cloudy days having lower vapor pressure deficit and higher diffuse-to-direct light intensity ratio. Data sets taken in this study over different time frames on whole canopy WUE provide a scenario quite different from that which might derive from traditional single leaf assessment reporting in almost all cases that intrinsic WUE (the ratio between leaf assimilation rate and stomatal conductance) increases under stress and suggests that methodology used can mask or alter conclusions made about adaptive response of grapevine cultivars to water stress. ER -