Differential effects of canopy manipulation and shading of vitis vinifera L. cv. cabernet sauvignon: Plant nutritional status

The effects of canopy manipulation and shading on crop quantity and quality as well as plant physiology in Vitis vinifera have already been studied by many authors while the plant nutritional status changes induced by such treatments present many unexplained aspects. Partial cluster and leaf removals were performed on Vitis vinifera L. cv. Cabernet Sauvignon at veraison (40% berries coloured) for two years to give four treatments: Control (C), Cluster Thinning (CT), Leaf Removal (LR), and Cluster Thinned + Leaf Removal (CT+LR) plots. At veraison, one half of these plots were shaded using a 50% shading net. The correlations between elemental contents of different organs showed that only potassium (K) in the leaves and stems were positively related, while for the other macro‐ and micro‐elements, no relationship or negative links were obtained. Shading needs only 14 days to modify the nitrogen (N) and phosphorus (P) in leaves. At harvest, N was depressed in leaves of cluster‐thinned vines and enhanced in leaf‐removed ones. Such changes are discussed on the basis of photosynthetic data which support the hypothesis that canopy manipulation involves modifications in both leaf biochemical and photochemical activities.