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 w ith 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 can opy development rate, canopy morphology, and crop load on whole-vine p hotosynthesis. Significant differences in canopy development rate, can opy morphology and dry matter partitioning occurred among treatments b ut whole-vine net photosynthesis (Pn) and dry matter production were n ot affected. Photosynthetic compensation by leaves of severely pruned vines enabled them to produce quantities of dry matter similar to vine s with greater leaf area. Vines bearing crop supported the development of berries by partitioning carbohydrate to fruit at the expense of ve getative tissues so overall vine dry weight was not different among cr opped and non-cropped treatments. Whole-vine Pn determinations were li nearly related to vine dry mass. By contrast, single leaf measurements used to estimate whole-vine Pn were not related to dry mass. If a sim ilar relationship can be demonstrated in field vines, it may be possib le to quantify the influence of biotic and abiotic stresses on vine bi omass production and subsequent yields.