The influence of soil moisture deficits on “Riesling” shoots in a cool, humid climate

Abstract

Water is not generally considered a limiting resource for viticulture in cool-climate regions, so often vineyards are not irrigated. However, recent climatic trends of higher average temperatures and erratic precipitation patterns are resulting in decreased soil moisture availability and, consequently, periods of vine water stress. Using mature, field-grown ‘Riesling’/101-14 grapevines (Vitis vinifera L.), we studied the effects of seasonal water stress on shoot growth, leaf gas exchange, xylem morphology, and hydraulic performance over two growing seasons in the cool-climate Finger Lakes region of New York. A plastic rain-exclusion tarp was installed on the vineyard floor to create a soil moisture deficit. This rain-exclusion gradually reduced soil moisture levels and imposed vine water stress as indicated by weekly measurements of predawn leaf and midday stem water potentials (Ψmd), respectively. Two contrasting shoot length classes, long (length > 2.0 m) and short (length < 1.0 m), were monitored. Differences in Ψmd and shoot growth between shoot classes were minimal, but growth of both long and short shoots was positively-correlated with Ψmd. Compared to rain-fed vines, water-stressed vines had lower photosynthesis and stomatal conductance later in the season when Ψmd dropped below -1.2 MPa. While no clear relationship was observed between xylem-specific hydraulic conductivity (Ks) and Ψmd, long shoots had three-fold higher Ks values compared to short shoots. An interesting and original finding was that long shoots tended to have lower hydraulic resistances in their cane-shoot junctions. Using ultrasonic acoustic emissions sensors and xylem histological techniques, we found that long shoots experiencing water stress were less vulnerable to xylem cavitation than shorter shoots even though they had more large-diameter vessels. The lower vulnerability to cavitation of long shoots may be attributed to less xylem inter-vessel pitting found in long shoots, consistent with the air-seeding hypothesis, and suggests a hydraulic advantage, enabling them to maintain superior growth and productivity under water stress.