Influence of shoot number and crop load on potted Chambourcin grapevines. 2. Whole-vine vs. single-leaf photosynthesis

Two-year-old potted Chambourcin grapevines were trained to one shoot with 0 or 1 cluster (1/0 and 1/1 respectively) or four shoots with 0 or 4 clusters (4/0 and 4/4 respectively) to determine the effects of canopy development rate, canopy morphology, and crop load on whole-vine photosynthesis. Significant differences in canopy development rate, canopy morphology and dry matter partitioning occurred among treatments but whole-vine net photosynthesis (Pn) and dry matter production were not affected. Photosynthetic compensation by leaves of severely pruned vines enabled them to produce quantities of dry matter similar to vines with greater leaf area. Vines bearing crop supported the development of berries by partitioning carbohydrate to fruit at the expense of vegetative tissues so overall vine dry weight was not different among cropped and non-cropped treatments. Whole-vine Pn determinations were linearly related to vine dry mass. By contrast, single leaf measurements used to estimate whole-vine Pn were not related to dry mass. If a similar relationship can be demonstrated in field vines, it may be possible to quantify the influence of biotic and abiotic stresses on vine biomass production and subsequent yields