A portable infra-red gas analyzer system was used to measure net photosynthetic rates on individual leaves of field-grown Vitis vinifera L. plants.
Generally, the leaf opposite to the upper cluster or all leaves of an average shoot were measured between 10:00 and 12:00. In Pinot noir (clone M 1/17) planted in 1985, there was a significant effect of training system early in the season: photosynthesis of high-trained cordon pruned vines was 27% lower than of low-trained either cane or cordon pruned vines.
However, this effect disappeared later in the season.
Leaf position within the canopy and, therewith, light availability on individual leaves became the predominant factor affecting photosynthetic rates, although the highest assimilation rates were measured in the middle part of the shoot and decreasing rates towards both the basal (source) and apical (sink) leaves.
When 3 leaves were removed in the cluster zone of Pinot noir vines 3 weeks after bloom, photosynthesis of the remaining leaves increased as compared to the removal of 6 or 12 leaves.
Six weeks after leaf removal net assimilation rates started to decrease.
This decrease was, however, the stronger the less leaves had been removed, indicating a delay in senescence of the remaining leaves after defoliation.
If the lateral shoots were consistently removed during the season, the main-shoot leaves responded by increasing their photosynthetic rates during the rest of the season and by a delay in senescence.
In Müller-Thurgau grapevines on 5C planted in 1988, with either 2 (control), 1 or 0 grape clusters after either early or late cluster thinning, no significant effect of crop load could be detected on leaf gas exchange.
Nevertheless, there was a clear trend towards higher photosynthetic rates in the control vines during the entire season.
Leaves in the upper part of the shoot (number 10 from the base) always assimilated at a higher rate than leaves in the cluster zone (number 4 from the base). The difference increased from 5% at bloom time to 65% at harvest.
Rootstocks markedly affected net assimilation rates of scion leaves in Müller-Thurgau planted in 1986, and there was a significant interaction with nitrogen fertilization.
Generally, 100 kg N/ha increased leaf gas exchange compared to non-fertilization.
However, this increase was minor in vines on 3309 and Ru 140, intermediate in vines on 5BB, 5C and 8B, and large in vines on SO4. In unfertilized vines the highest photosynthetic rates were found on 5BB, which were similar to the