Upscaling leaf gas exchange measurements to the whole grapevine canopy: An update

This review first revisits current knowledge about single-leaf function, viz. photosynthesis, chiefly in relation to environmental factors, that underscores the importance of multiple summer stresses. Emphasis is placed on the response different genotypes show under light and heat stress with or without soil-water shortage. Secondly, it tackles the thorny issue of extrapolating single-leaf readings to the whole-canopy level, with special reference to both methodological and physiological implications. Whole-canopy gas-exchange systems deliver and emphasise the usefulness of such an approach in achieving key research goals. One case in point is quantifying the amount and dynamics of canopy gas exchange in response to summer pruning, which alters a canopy's leaf population. Other examples show how useful a whole-canopy approach can be in monitoring diurnal or seasonal variation in light interception, photosynthesis and water use, or when the need is for an objective validation tool to assess the precision of models devised to predict carbon budget. The discussion of some of these case studies attempts to explain why conclusions driven by single-leaf surveys can at times diverge from those derived from a whole-canopy approach. The overall intent of the review is to highlight the single-leaf approach, especially when performed under a methodology suitable to the objectives, as well as the effectiveness of the whole-canopy approach, even limited by the small number of replicates, in understanding the whole vine behaviour. Indeed, the bottom line seems to be that conducting both single-leaf and whole-canopy measurements in the same experimental plot is an added value to research and can be reliably employed to judge the efficiency of different training systems