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60 p r a c t i c a l w i n e r y & v i n e ya r d J U n e 2 0 1 4 g r a p e g r o w i n g Phone (805) 239- 4989 Fax (805) 239- 4988 www.MichaelDusiTrucking.com FOR ALL YOUR TRANSPORTATION NEEDS TANKERS • REEFERS • VANS FLATBEDS • LOWBEDS MichaelDusi_Dir10 11/18/09 12:40 PM Page 1 SUPPLIERS OF QUALITY VIRUS CERTIFIED GRAFTED GRAPEVINES Deadline for Custom Grafted Order For Spring Planting is January of Previous Year For Further Information & Pricing Please Call or Write 1912 Concession 4 R.R. #2 Niagara-on-the-Lake Ontario, Canada LOS 1J0 Phone: 905-468-0822 Fax: 905-468-0344 Mori_Nov05.qxt 9/19/05 3:29 PM Page 1 sible to know the partitioning of S n between rehydration (water that remains in wood and organs), cuticular transpira- tion (smallest component) and transpira- tion through stomata within leaves. An indirect method to characterize this par- titioning has been proposed by S. Fuentes et al. comparing S n data with the atmo- spheric demand for water as nighttime vapor-pressure deficit (VPD). 11 When comparing S n data from the first zone (Figure 2) with nighttime VPD and the corresponding values for the second zone of the curve with night- time VPD, it was found that there were high correlations between S n and VPD in Zone 1, but no correlations at all for Zone 2. 11,18 The observations have been supported by collecting gas-exchange measurements of E night and G night with accurate and sensitive instrumentation at night. 9 Furthermore, Zone 2 of the curve is characterized by high ABA levels in the sap (Fuentes et al., unpublished). There- fore, it could be speculated that G night and E night in Zone 1 is more influenced by hydraulic signals (VPD and Ös) and Zone 2 by hormonal signals (ABA). Implications of nighttime transpiration and rehydration in the whole-plant water budget Rehydration at night helps the plant recover from water stress endured the previous day to maintain cell turgor for Figure 2. nighttime water uptake (s n ) response to plant water status measured the previous day for fully irrigated grapevines cv. shiraz (Benalla, Victoria. Australia). two zones are characterized for non-water stress to mild water stress (Zone 1) and from mild water stress to severe water stress (Zone 2), (Fuentes et al. under review). 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 S n (L vine -1 night -1 ) s (MPa) Zone 1 Zone 2