Impact of training system on gas exchanges and water use efficiency: A 3D-modelling study with TopVine

Abstract

The impact of canopy structure on spatial leaf area distribution, canopy microclimate and fruit quality has been widely studied. However, the potential damage on grapevine physiology produced by the increasing environmental constraints observed on many regions worldwide; claims for a new approach in order to develop new adaptive management strategies. During the last years, the development of three-dimensional representations of plants combined with microclimatic and physiological models has opened new opportunities to explore the adaptation of vine canopy structure to environmental constraints.

In this study, we combined a 3D modeling approach simulating canopy structure with a gas-exchange model built at the leaf level to analyze the interactions between canopy structure and gas-exchanges at the whole plant level. Our objectives were (i) to quantify canopy net carbon exchange (NCE) and transpiration (Tr) rates for a large range of trellis system and (ii) to evaluate the relative contribution of sunlit and shaded fractions of leaf area to NCE, Tr and water use efficiency (WUE). The model was parameterized for four training systems differing in canopy height, shoot positioning, planting density or canopy structure (single or divided canopies).

Our results showed a linear relationship between NCE, Tr and light intercepted that was common for all systems studied. Water use efficiency seems to be driven by light distribution within the canopy. In this regard, the shaded part of leaf area plays a major role. These leaves contributed little to NCE, but their contribution to Tr reached up to 35% indicating that training systems with a higher proportion of sunlit leaves will have a higher WUE. These results highlight the major role played by trellis system on the trade-off between carbon acquisition and transpiration at the canopy level.