The review paper initially revisits current knowledge about single leaf function, namely photosynthesis, as mostly related to environmental factors including multiple summer stresses. Emphasis is placed on the response that different genotypes show under light and thermal stress with or without a combination of water shortage in the soil. Then it tackles the challenging issue of extrapolating single-leaf readings to the whole canopy level with special reference to both methodological and physiological implications. This part deals with “data types” which are delivered from whole-canopy gas exchange systems and emphasises the usefulness of such approach, for example, for characterizing canopy gas exchange in response to summer pruning. Moreover, other examples show how useful a whole-canopy approach can be if the research goal is monitoring diurnal or seasonal variation of light interception, photosynthesis and water use, or when the goal is to assess the degree of precision of models for carbon balance. Yet, some of the case studies discussed here explain why conclusions driven from single-leaf based surveys in some instances diverge from those derived from a whole-canopy approach. Overall, this review paper does not indeed disqualify the single-leaf approach (especially if performed under a methodology suitable to the objectives) and, on the other hand, acknowledges some inherent limitations of the whole-canopy approach (i.e. limited number of replicates allowed, lack of marketed systems). Yet, the melting point seems to be that conducting both single-leaf and whole canopy measurements on the same experimental plot brings an added value to research and, for example, can be reliably used as a tool to judge efficiency of different training systems.
Keywords: photosynthesis, transpiration rate, assimilate partitioning, summer pruning, training systems, chlorophyll fluorescence, photo-inhibition