Photosynthesis and water relations of grapevines growing in Portugal - response to environmental factors

Grapevine (Vitis vinifera) is a perennial crop plant grown mostly in mediterranean type climate zones. The water requirements of the crop are provided in most situations by winter rains. Deep root systems are a feature of grapevines which allow ground water absorption during the dry period. Nevertheless, plants in many vineyards in Portugal are exposed to conditions of water and temperature stress during the summer period. We can assume that grapevine cultivars, adapted to hot dry summer conditions, have been selected for naturally and by man since early periods of cultivation, in the Douro Valley possibly as early as A.D. 55 (Olmo 1976).