A comparative physiological study of three red varieties in the Demarcated Douro Region

In certain regions, especially those with a Mediterranean climate, that are highly susceptible to climate change, viticulture is expected to become less suitable for the production of high-quality wines. From an evolutionary perspective, grapevine varieties have evolved genetic adaptations in the form of protective mechanisms to withstand summer stress, reflecting the climatic conditions in which grapevines were initially domesticated. The in-depth knowledge of the structural and functional characteristics of grapevines can aid in the identification and selection of varieties that are better suited to adverse environmental conditions and to the increasingly challenging conditions imposed by climate change. Following, this study aims to evaluate the extent to which the water status adjustment and the leaf biophysical and biochemical processes influence the respective photosynthetic performance of a currently neglected grapevine variety, Tinto Ca similar to o (TC) and two commonly used varieties in the Douro region, Touriga-Nacional (TN) and Tinta-Roriz (TR). The experiment was undertaken in the BaixoCorgo sub-region of the Demarcated Douro Region in the north of Portugal. Grapevine water status, chlorophyll contents, leaf reflectance indices, chlorophyll a fluorescence (modulated and transient) and leaf gas exchange (including A/PPFD and A/Ci curves) were evaluated in three different phenological stages. The results indicate that, compared to TN and TR varieties, the TC minimizes the light-harvesting system while promoting thermal energy dissipation, which can be interpreted as photoprotective mechanisms at the photosynthetic apparatus level. These mechanisms imply the downregulation of the photochemical reactions but without significant losses of net productivity compared to TN, while TR remained increased. Despite the minor expression of Tinto-Ca similar to o nowadays, this variety can also have great adaptability for very hot and sunny wine-growing regions.