|Perez Pena, Jorge - WASHINGTON STATE UNIV|
|Keller, Markus - WASHINGTON STATE UNIV|
Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 16, 2005
Publication Date: August 30, 2005
Citation: Tarara, J.M., Perez Pena, J.A., Keller, M. 2005. Using whole-vine photosynthesis to understand the effects of water deficit on premium wine grapes. Acta Horticulturae. 689:301-307. Interpretive Summary: Wine-grape vineyards that produce fruit for the premium quality market are often managed under a practice called Regulated Deficit Irrigation, or RDI. Regulated Deficit Irrigation is a technique of deliberately irrigating a field with less water than the plants need, so that the plants suffer "water stress." Applied judiciously, this water stress can induce desirable plant responses. In the case of wine grapes, these responses include fewer leaves, shorter shoots, and smaller grape berries. These responses are desirable because less vegetation means more exposure to sun and better ripening for grapes; smaller berries increase the skin-to-juice ratio of the fruit. The color and many of the compounds needed for high quality wine are found in grape skins, not the pulp. Grape growers need to know when they should apply deficit irrigation to the vineyard, for how long, and to what extent they can impose water stress on the plants to achieve the benefits of RDI without negative effects. By measuring photosynthesis and transpiration in commercial vineyards under RDI, we can provide information to growers so they can estimate appropriate timing, duration, and severity of water stress as they make decisions about irrigation management.
Technical Abstract: Whole-vine photosynthesis and transpiration were measured on 18 vines (field-grown, own-rooted, drip irrigated Vitis vinifera cv. Cabernet Sauvignon) under three regimens of regulated deficit irrigation (RDI): 1) standard RDI (weekly application equivalent to 70% of estimated well-watered vine evapotranspiration [ETw]); 2) early deficit (weekly application equivalent to 35% of vine ETw between fruit set and veraison, then return to standard practice); and 3) late deficit (standard practice until veraison, then weekly application equivalent to 35% of vine ETw until harvest). Whole-vine chambers were deployed for 7-day measurement runs during physiologically important stages: fruit set, pre- and post-veraison, and pre- and post-harvest. After harvest, all vines were well watered until leaf fall. Large differences were observed in net carbon exchange and in transpiration between vines under standard RDI and those under additional water deficit. Before veraison, early-deficit vines fixed over 40% less carbon each day and transpired up to 46% less than vines under standard RDI when integrated over 24 h. After veraison, vines under the late deficit transpired up to 38% less than their standard RDI counterparts. Early deficit vines, although watered at the standard RDI rate, did not appear to completely recover in terms of daily carbon fixed and water transpired. In late-deficit vines, after two to three irrigation cycles under the deficit, reductions in carbon assimilation and transpiration were proportionately similar to those observed in the early-deficit vines before veraison.