Physiological Efficiency and Adaptability of Greek Indigenous Grapevine Cultivars Under Heat Stress and Elevated CO: Insights into Photosynthetic Dynamics.

This study investigates the impact of climate change on key physiological parameters of Greek indigenous grapevine cultivars (Savvatiano, Muscat, Assyrtiko, Mavrodafni, Moschofilero, and Agiorgitiko), using Sauvignon blanc and Merlot as benchmarks. The aim was to identify genotypes with higher photosynthetic dynamics and water use efficiency (WUE) under heat stress and to examine the role of CO enrichment in modulating these responses. Gas exchange measurements showed that short-term exposure to elevated CO (e[CO]) (i.e., 700 ppm) enhanced photosynthesis by 37-64%, 77-89%, and 18-68% under control, moderate, and severe heat-stress regimes (23, 35, and 40 °C), respectively. CO enrichment also improved WUE by 61-122%, 96-138%, and 11-63%, with the greatest benefits at 30-33 °C, depending on genotype. Cultivars with strong CO-saturated photosynthetic capacity and small stomata, such as Sauvignon blanc and Mavrodafni, showed greater photosynthetic stimulation and WUE improvement from CO elevation. Stomatal traits influenced photosynthesis under ambient CO (a[CO]) but not under e[CO]. Of the white varieties examined, Sauvignon blanc and Savvatiano showed the best performance under combined e[CO] and heat stress, while Assyrtiko and Muscat adapted better to high temperatures at a[CO]. Among red cultivars, Mavrodafni showed the highest photosynthetic efficiency at both CO conditions, even under heat stress. The present findings indicate that grapevine varieties exhibit differential responses to elevated temperature and CO levels. A comprehensive understanding of grapevine responses to stress conditions is therefore essential for the selection of cultivars with enhanced adaptation to climate change.