Photosynthetic and Photoinhibition Behavior of Two Field-Grown Grapevine Cultivars under Multiple Summer Stresses

Abstract

The identification of drought-resistant genotypes of Vitis vinifera that can optimize their water use is attracting increasing interest, especially in areas where it is difficult to extend irrigation and that are undergoing a progressive shift toward subtropicalization. This study was carried out in 2003 (a year characterized by severe drought conditions) and 2004 (characterized by absence of drought conditions) to evaluate the changes in morphostructural characteristics and physiological behavior of two red grapevine cultivars widely cultivated in Italy: Sangiovese and Montepulciano. Unlike 2004, data recorded during 2003 showed that, contrary to Montepulciano vines, the vertical shoot-positioned canopy of Sangiovese vines was divided into two different zones. The basal zone was close to the fruiting zone, featured low carbon gain, and was characterized by 57% of leaves affected by chlorosis and necrosis, while the remaining leaves were affected by chronic photoinhibition (Fv/Fm <0.50). The upper zone was characterized by high photosynthetic activity and water-use efficiency. The changes in leaf inclination and lower leaf absorption and the greater leaf transmittance in Sangiovese leaves appeared to help in the avoidance of excessive light and heat absorption. Irrespective of their positions, the leaves of Montepulciano promptly closed their stomata and saved water, while reducing their physiological activity. Results indicate that grapevine strategies in response to multiple and severe summer stress conditions are a function of genotype, leaf age, and leaf position along the shoot. Unlike Montepulciano, under drought conditions, Sangiovese can be considered to be well adapted, since it can optimize the whole-vine carbon gain.