Structural memory in grapevines: Early season water availability affects late season drought stress severity

In the future drought events are expected to occur more frequently, with unpredictable rain and heat events. In current research we investigated how different water availability patterns influenced late season plant water status in Vitis vinifera. ‘Cabernet Sauvignon’ grapevines were grown for three consecutive years. We compared the response to five water availability regimes: High, Intermediate, Low (along all season) and High-to-Low (High during the beginning of vegetative seasons switched to low during the rest of season) and Low-to-High (opposite treatment). Midday stem water potential (SWP) was measured weekly to determine the seasonal pattern of drought stress. Xylem anatomy was investigated by trunk vessel diameter measurements, and specific axial xylem conductivity was calculated according to Hagen-Poiseuille's law. Vines exposed to high water availability treatment showed improved seasonal water status along the season, compared to vines in the low treatment. Vines exposed to High-to-Low water regime showed a markedly improved water status at the beginning of the season, but became the most severely stressed toward the end of season. The SWP values were more negative in the High-to-Low regime even when compared to the Low water regime. Water availability at the beginning of the season (during main period of cambial activity) determined the vessel characteristics: high water availability during cambial activity increased vessel diameter and thus specific hydraulic conductivity. Our data strongly indicates that regulated drought stress can be induced by manipulating xylem structural parameters via controlling water availability during the period of stem cambial activity.