| Influences of water deficits in grapevines have been studied worldwide in recent years because of their influence on wine quality and water savings. To approach these issues, grape growers have adopted regulated deficit irrigation (RDI) that consists of applying less water than full vine evapotranspiration (FVET) to limit water use to that amount just needed to ripen the crop, achieve the fruit characteristics demanded by winemakers, and end the season with a plant prepared for winter and the following budbreak. For a better understanding of RDI on vine physiology, whole-canopy gas exchange rates (CO2 and H2Ov) were measured by a six-chamber, mobile field laboratory designed, built, and tested in 2001. Measurements were taken in 2002 and 2003 at five times during the season (fruit set, pre- and post-veraison, and pre- and post-harvest) in a drip irrigated vineyard of cv. Cabernet Sauvignon under three regimens of RDI: (1) standard deficit (S; replacement of 70% of FVET); (2) early deficit (E; replacement of 35% of FVET between fruit set and veraison); and (3) late deficit (V; replacement of 35% of FVET between veraison and harvest). At the same time, single-leaf photosynthesis and transpiration were measured. Effects of those regimens on carbohydrate dynamics were studied by sampling leaf tissue and dormant canes for determination of non-structural carbohydrates. Vine canopies under additional water fixed less CO2 and transpired less water than those under standard deficit. Reductions were associated with lower canopy conductance. Vines under additional water deficits (E, V) had lower leaf starch concentrations in the afternoon, but no differences in soluble sugar concentrations. Pruning weights in S and V vines were up to 41% higher than those of E vines. No differences were found in water use efficiency nor intrinsic water use efficiency among irrigation regimens. Reductions in irrigation and water use occurred at the expense of reductions in carbon fixation. No consistent effect of additional water deficits were recorded on fruit yield or quality. A novel deficit irrigation index based on monitoring transpiration and vapor pressure deficit is proposed. |
