|Authors: ||J.M. Tarara, J.E. Perez Peñ, M. Keller|
|Keywords: ||Vitis vinifera, transpiration, net carbon exchange, regulated deficit irrigation|
Whole-vine photosynthesis and transpiration were measured on field-grown Vitis vinifera L. ‘Cabernet Sauvignon’ under three treatments of regulated deficit irrigation (RDI): 1) standard RDI (weekly applied water at 70% of estimated well-watered vine evapotranspiration [ETw]); 2) early deficit (weekly water applications at 35% of ETw between fruit set and veraison, then a return to the standard treatment); and 3) late deficit (standard treatment until veraison, then weekly water applications at 35% of ETw until harvest). All vines were well-watered from harvest to leaf fall.
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.
Large differences in net carbon exchange and transpiration were observed between vines under standard RDI and those receiving less applied water.
Prior to veraison, early-deficit vines fixed 40% less carbon and transpired up to 46% less each day than did vines in the standard treatment, when integrated over 24 h.
After veraison, transpiration was 38% less for the late deficit treatment compared to the standard treatment.
Even though the early deficit vines had been irrigated at the standard RDI rate, at this time they did not appear to have completely recovered 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 that had been observed in the early-deficit vines before veraison.
Only small differences in photosynthesis and transpiration were detected among treatments before and after harvest, when daytime temperatures were lower and day-length was shorter than at veraison.
A longer deficit applied between fruit set and veraison reduced seasonal irrigation by 38% with no apparent negative impact on fruit quality, suggesting that reduction in irrigation below current levels of RDI can be accomplished in this region without negative impact on fruit.
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