Root and stem water dynamics of rainfed grapevines in the Douro region

Soil water availability influences grapevine physiological processes, such as photosynthesis, transpiration, transport and accumulation of assimilates and mineral nutrients, and consequently grapevine yield and fruit quality. In this way, the understanding of grapevine survival strategies is critical, particularly in Mediterranean-type climates, which are characterised by hot and dry summer conditions. The water dynamics of field grown grapevines (Vitis vinifera L. 'Semillon') was studied in the Douro Demarcated Region (northeast of Portugal) during the 2012 growing season. The compensated heat-pulse (CAG) method was used to continuously monitor sap flow in stems and roots of non-irrigated mature plants. Following transpiration depression (particularly around midday) during the drier periods of the season, clear increases in stem sap flow and other related responses were observed after late summer rains, indicating plant water stress prior to rainfall, and a subsequent recovery shortly thereafter. Additionally, significant nocturnal sap flow was observed in both stems and roots, and was related to high vapour pressure deficits associated with warm, windy nights. These nocturnal flows may also be associated with rehydration dynamics and plant water management. The possible existence of negative flows (reverse flows) is examined.