INFLUENCE OF DEFOLIATION, ROOTSTOCK, TRAINING SYSTEM, AND LEAF POSITION ON GAS-EXCHANGE OF PINOT-NOIR GRAPEVINES

A factorial design was used to vary defoliation, rootstock, and traini ng system of Pinot noir grapevines during two seasons. Defoliation con sisted of 0, 6, or 1 0 leaves removed acropetally f rom the shoot base six weeks after full bloom (pea-size). 3309C and 101 -1 4 Mgt were us ed as rootstocks, and the training systems used were the traditional l ow-head, cane-pruned system (double Guyot), or a variant trained to di vided trunk which had a greater amount of two-year-old and older wood. Leaf positions sampled periodically were: (1) the leaf opposite to th e basal cluster; (2) the 11th main leaf f rom the base; and (3) the th ird leaf of one of the top lateral shoots. Gas exchange measurements w ere conducted in both the season of the defoliation and the following year when no stress was applied to the vines. Defoliated vines showed similar photosynthetic rate per unit leaf area compared to non-defolia ted controls in either season. Defoliation also had little effect on t ranspiration rates and water use efficiency during both seasons. Leave s from lateral shoots and leaves from the main shoot at the surface of the canopy had similar photosynthetic and transpiration rates during both seasons. Leaves opposite to the clusters had declining photosynth etic rates as fruit matured. They also showed lower transpiration and water use efficiency compared to leaves located at the top of the cano py. Generally, plants grafted to 101-14 Mgt had higher CO2 assimilatio n, transpiration rates, and higher water use efficiency than vines on 3309C. Plants with single trunk showed an improved gas exchange perfor mance over those with divided trunk. Leaf chlorophyll content during t he ripening period of the recovering season showed the same tendencies as observed for photosynthesis.