WineEast
Thus the chloroplasts are protected from
overproduction of their light-capturing
function when water becomes a limiting
constituent in a leaf's survival.
This limitation starts happening as the
temperature in the vineyard climbs above
85oF, with photosynthesis completely shut
off above about 95oF. The dryer the air, the
higher the evapotranspiration rate in the
leaves and the lower the water potential of
the leaf; thus, the shutdown can be at lower
temperatures in dry climates than in more
humid climates.
If, on any given day during the growing
season, a particular leaf has a localized
water stress, either from being in direct
sun or some other more global effect on
the plant (such as a lack of water from the
soil environment), then that is going to
affect the overall efficiency of the plant's
energy production.
Through this knowledge of the
leaf functioning during the day, it is
reasonable to expect that in plain daylight
growing conditions, a grape leaf can have
reduced energy production efficiencies
in what we have thought is a perfectly
78 W in es & V i ne s J U NE 2 013
Grapes grown in a tunnel that has the correct plastic barrier are exposed to reflected light that
bounces around the inside of the tunnel.
good environment: long, warm, sunny
days. The effect on grapevines growing
in a classic Mediterranean climate is
to have carbohydrates produced during
early and later times of the day, with
significant parts of the middle not
H&W_Dec10.qxp
performing at a maximal rate. In a
climate like the eastern United States,
energy production may not operate at
the maximal rate for longer times of the
day than Mediterranean climates, but
with higher humidity, the slightly lesser
intensity 10:59 AM Page 1
10/12/10 of the sun should let the net
carbohydrate production be at least close,
