Canopy structure and photosynthesis modelling of grapevines (Vitis vinifera L. cv. Sultana) grown on an overhead (parronal) trellis system in Chile

摘要

Most table grapes in Chile are produced on an overhead (parronal) trellis system with typically high values for leaf area index (LAI). An apparent lack of sunlight inside such canopies often raises questions as to the photosynthetic effectiveness of shaded leaves, and the comparative importance of successive leaf layers (top to bottom) for the total canopy carbon balance. In particular, are some leaves parasitic with respect to daily carbon balance? Accordingly, we undertook a study of canopy architecture, light climate and photosynthetic physiology to address those issues. Canopy photosynthesis was inferred from a process-based model using measured values for: the vertical distribution of (1) leaf angle, (2) LAI, (3) the fraction of sunlit leaves and (4) single-leaf photosynthetic capacity. Photon flux densities (PFD) and measured values of CO_2 assimilation by leaves located on different parts of the canopy were obtained at flowering (mid-October) and during active berry growth (mid-December). Results of leaf angle revealed that Sultana canopies on this system behave in an erectophile manner with an average leaf inclination of 60° above horizontal. Modelling the contribution made by different leaf layers to overall canopy photosynthesis demonstrated that leaf layers contributing most were those under a shade plus sunfleck regime. They were located between 20 and 40 cm above the horizontal trellis structure itself. Indeed, some photoinhibition was observed in leaves under continuous direct radiation towards the top of the canopy, and located above 40 cm layer. However, such leaves represented only a small proportion of total LAI, and thus compromised canopy photosynthesis to only a limited extent. Outcomes from our simulation studies imply that LAI values commonly reached by canopies managed according to the parronal system of grape trellising do not result in parasitic leaves.