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Figure 7: Seasonal evolution of transpiration in plot 1 (vineyard at V. Santarém, Portugal), during Spring-Summer 1996 and 1997.

Differences between the years were related with meteorological conditions verified: higher variations of T rates in 1997 due to the atypical meteorological conditions with important rain events during summer contributing to reduce water stress (Silvestre at al., 1999). This is shown by the seasonal trend of T/ETo (Figure 8), consistent with the evolution of water stress indicators (e.g. Figure 9), as predawn leaf water potential measured with a Scholander pressure chamber (see Section 5) and stomatal conductance (not shown). For the period of veraison (beginning of sugar accumulation) and maturity, the T/ETo decrease was less important in 1997, as a consequence of the precipitation occurred. T/ETo decreased earlier in 1996 and, at the end, was roughly half of the 1997 T/ETo values.

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