Gas exchange of field-grown <em>Vitis vinifera</em> L. cv. zweigelt leaves in relation to leaf age and position along the stem

Aims: The study aimed to investigate the effects of leaf age and position along the stem on the seasonal evolution of photosynthesis and water use efficiency (WUE) of primary leaves of field-grown grapevines (Vitis vinifera L. cv. Zweigelt) under natural growing conditions in the Pannonian climate. Methods and results: Single-leaf gas exchange measurements were carried out in three vineyards with different planting densities, training systems and canopy management in the Neusiedlersee region (Burgenland, Austria). From the beginning of leaf development until flowering, basal leaves in the fruiting zone showed the highest photosynthetic activity. After flowering until ripening, the zone with the highest photosynthetic activity continuously moved in the apical direction. Leaves reached their maximum photosynthetic activity 30 to 40 days after emergence, depending on investigation site and vineyard management. Due to sufficient water supply, photosynthesis of old leaves decreased slowly; thus 100 days after unfolding leaves still retained 65% to 75% of their maximum photosynthetic activity. Conclusion: The development of single-leaf photosynthesis in the Zweigelt grapevine corresponded to the results of prior investigations on other grape varieties. However, vineyard management strongly influenced the evolution of gas exchange during the growing period. Leaves from vines stressed by high crop load or poor canopy management showed early leaf senescence and a strong decline in photosynthetic activity after reaching maximum level. Well-watered leaves from shoot-thinned vines with moderate crop load and equal light exposure throughout the canopy exhibited high photosynthesis with a much slower decrease in older leaves. Significance and impact of the study: The results indicate that under favourable growing conditions ensured by adequate water supply and canopy management, basal leaves maintain good photosynthesis and WUE over a long period of time. Thus old leaves, as well, can contribute to the photosynthesis of the entire vine.