Evaluation of low-energy demand adaptive mechanisms in Sangiovese grapevine during drought.

Aims: The aim of this paper is to evaluate the photoinhibition capability, CO2 fixation activity and some adaptive mechanisms external to the photosystem II reaction centres in Sangiovese grapevine subjected to drought conditions. Methods and results: The diurnal time courses of gas-exchange and chlorophyll fluorescence parameters were monitored on free (natural position) and artificially retained (horizontal) leaves in Sangiovese potted vines maintained at 90 % and 40 % of maximum water availability from fruit-set to veraison. Changes in leaf and shoots characteristics were also monitored. Under drought, the inhibition of photosystem II in Sangiovese leaves may be severe and persistent according to leaf position (basal leaves with chlorosis and necrosis) and ability to avoid direct light (medial leaves with a more vertical position followed by lower temperatures and higher CO2 fixation capability and water use efficiency during the hottest hours of the day). Conclusion: In the Sangiovese leaves developed under drought, the protective effect of increasing leaf angle with a more vertical position and the energy costs saved by reducing photosynthetic pigments formation, changing leaf optical properties, diminishing xylem and shoot growth and leaf area development and limiting down-regulation of photoassimilation help maintain high physiological efficiency in all the distal leaves. Significance and impact of study: The results indicate that cultivar Sangiovese exhibit high adaptation to dry conditions.