Proceedings - IX International Terroir Congress, 2012Aiming to compare the physiological responses of the Portuguese red variety Touriga Nacional (TN) with Syrah (SY),
we studied during the 2007 growing season five-year-old grapevines growing in a commercial non-irrigated vineyard
located at the Lisbon winegrowing region. Predawn (Ypd) and midday (YM) leaf water potential, leaf stomatal
conductance (gs) and photosynthetic rate (A) were periodically measured between fruit set and harvest. Ypd displayed a
decreasing pattern throughout the growing cycle from -0.10 MPa at flowering to -0.44 MPa at harvest. Both varieties
showed similar values except during the two measurements made in August when TN presented significantly higher
values than SY. Ymid also showed a decreasing pattern from the end of June towards harvest date, with significant
differences between varieties being observed during the ripening period, with SY showing lower values than TN. A
measured either at mid-morning and midday presented, for most part of the cases, lower values in SY than in TN,
although the differences were only significant during the ripening period. gs pattern was parallel to A and, in general,
the relative differences between varieties mirrored those reported for A. No significant effect of the variety was detected
on the relationships between A or gs measured at mid-morning and Ypd. However, when analyzing the set of data
collected at midday it was observed that the regression lines of the relationships between A or gs (dependent variables)
and Ypd (independent variable) presented a significantly higher slope in SY as compared to those showed by TN. These
results show that the rate of decrease of A and gs with the decrease of Ypd was lower in TN than in SY suggesting that
the two varieties have different stomatal regulation, with a more “optimistic” behavior in TN
