Predawn leaf water potential, night respiration, stomatal
conductance, transpiration, and photosynthesis of
4 grapevine cultivars were assessed under irrigated and
non-irrigated conditions in July, August and September
1994. Predawn leaf water potential was not significantly
related to either stomatal conductance or photosynthesis.
Water stress induced distinct stomatal closure in all
cultivars at 11 a.m. For a given stomatal conductance rate,
photosynthesis of stressed vines was lower than that of nonstressed
vines. At similar stomatal conductance rate, photosynthesis
was lower in cv. Chardonnay than in any other
cultivar. Photosynthesis was the physiological parameter
mostly affected by water stress. Dry matter production was
linearly related to stomatal conductance, photosynthesis,
and the night respiration to photosynthesis ratio for all
vines pooled together. In contrast, under stress conditions
dry matter production was not related to any physiological
parameter.