Scaling up photosynthetic water use efficiency from leaf to whole plant in table grapevine trained to tendone system

Scaling up photosynthetic gas exchange from leaf to whole canopy is an important objective of ecophysiological studies, but it is difficult to realize due to both the complexity of the leaf arrangement and light distribution inside the canopy. In this study, Southern Italian field-grown table grapevines trained to overhead horizontal trellises (tendone) were evaluated for net CO2 uptake and leaf transpiration on undisturbed single leaves (SL) of different canopy layers in dense and sparse canopy portions or on the whole canopy (WC) enclosed in a plastic balloon. Photosynthetic leaf water use efficiency, considered a good indicator of water use efficiency of biomass productivity, was calculated as the A:E ratio. The diurnal pattern of whole canopy net CO2 assimilation showed higher values than those found in single leaf. This difference could be partially related to the increased diffused and reflected light inside the plastic enclosure, which is known to increase the photosynthetic level of shaded leaves; on the other hand, this difference might indicate the necessity to improve single leaf measurements by selecting leaves which better represent the natural complexity of foliage. Differences between single leaf and whole canopy transpiration were attenuated, most likely due to a lesser influence of light on transpiration than on CO2 assimilation. Single leaf and whole canopy water use efficiency were similar during the central part of the day, while during early morning, whole-canopy water use efficiency was particularly overestimated possibly due to the different measurement systems. A multiple regression analysis demonstrated that a significant difference between SL and WC leaf photosynthetic water use efficiency was established, permitting the scaling up from single leaf to whole canopy, which was the principle aim of this research. Both dense and sparse canopy data, not only their weighted averages, were needed to reach a significant scaling up.