Drought-induced changes in xylem vessel size and distribution of field grown Syrah grapevines

Abstract

Drought-induced changes in vessel size and distribution and shoot hydraulic conductivity were investigated in field-grown Syrah grapevines (Vitis vinifera L.) in Northern Greece. Three irrigation regimes, replicated four times, were applied from berry set through harvest: full irrigation (FI: 100% of crop evapotranspiration), deficit irrigation (DI: 30% of crop evapotranspiration) and non-irrigated (NI). Water potential (Ψ) and gas exchange parameters were measured on fully expanded leaves during the growth period. After leaf fall, ten canes per plot were sampled and transverse shoot hand-cut sections of about 0.5 mm thickness were directly examined on a microscope equipped with digital camera. Shoot and xylem cross-sectional areas and number and size of single vessels were measured at internodes 3, 8 and 19 from the base of the shoot, on the digital images taken. Predawn Ψ decreased with increasing drought, with significant differences among treatments. Average shoot diameter and xylem area were higher in FI, in all internodes. Overall, FI vines had higher vessel diameter and total vessel frequency in all shoot sections. However, the xylem tissue of NI and DI plants had significantly more vessels in the 40–60, 60–80, 80–100 and 100–120 μm classes than FI, mainly in the basal and middle part of the shoot. In contrast, FI plants had significantly more vessels per xylem area in the largest diameter classes (120–140, 140–160, 160–180, 180–00 and >200 μm). For the diameter classes superior to 140 μm, NI vines had no vessels. The relative conductivity of the xylem tissue decreased with water deficit. This was explained by both a reduction in vessel diameter and vessel frequency, especially of the large diameter classes. The decrease in size and number of xylem vessels under low water availability may contribute to the control of water flow along the soil-plant-atmosphere pathway.