Influence of Defoliation, Rootstock, Training System, and Leaf Position on Gas Exchange of Pinot noir Grapevines

Abstract

A factorial design was used to vary defoliation, rootstock, and training system of Pinot noir grapevines during two seasons. Defoliation consisted of 0, 6, or 10 leaves removed acropetally from the shoot base six weeks after full bloom (pea-size). 3309C and 101-14 Mgt were used as rootstocks, and the training systems used were the traditional low-head, cane-pruned system (double Guyot), or a variant trained to divided trunk which had a greater amount of two-year-old and older wood. Leaf positions sampled periodically were: (1) the leaf opposite to the basal cluster; (2) the 11^th main leaf from the base; and (3) the third leaf of one of the top lateral shoots. Gas exchange measurements were 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-defoliated controls in either season. Defoliation also had little effect on transpiration rates and water use efficiency during both seasons. Leaves 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 photosynthetic rates as fruit matured. They also showed lower transpiration and water use efficiency compared to leaves located at the top of the canopy. Generally, plants grafted to 101-14 Mgt had higher CO₂ assimilation, transpiration rates, and higher water use efficiency than vines on 3309C. Plants with single trunk showed an improved gas exchange performance over those with divided trunk. Leaf chlorophyll content during the ripening period of the recovering season showed the same tendencies as observed for photosynthesis.