Figure 2. VitiSim simulations of the carbon demand for crop growth of Concord vines with 100 shoots or 350 shoots per vine and long-term
Geneva, NY weather.
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b) evaluate
the effects of daily weather or longterm
climate patterns and different
stress and cultural factors on these
patterns; and c) try to determine if and
when critical periods of carbon supply
and demand occur, especially in relation
to fruit development and ripening.
Seasonal demand dynamics
In mature vines, the vast majority
of net seasonal dry matter assimilated
goes into current growth (leaves,
shoot stems, and crop). In this example,
we present model simulations of
healthy, unstressed, heavily-cropped
Concord grapevines (spaced 8 x 9 feet)
with industry standard 100 shoots per
vine (yield of about 9 tons per acre)
compared to minimally-pruned vines
with 350 shoots per vine (yield of
about 12 tons per acre).
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Seasonal patterns of supply and
demand are distinct. The carbon
demand of growing shoots show a single
peak around or after bloom. This
peak demand occurs earlier in vines
with higher node numbers and later in
vines with fewer shoots that grow
longer into the season (Figure 1). The
demand pattern for the crop is a double
peak, with a peak a few weeks
after bloom during berry cell division,
followed by a decline during the lag
period (Figure 2).
After veraison, the second peak of
demand occurs very rapidly, and then
declines with ripening. Shoot numbers
affect the timing of peak demand.
However, different crop levels affect
the amount, but not the timing, of crop
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demand in our simulation. Root growth
patterns have been reported to
be variable, but likely reflect a weak
sink throughout the growing season.6
Seasonal carbon supply and
supply/demand balances
The seasonal pattern of supply is
relatively simple, peaking between
bloom and veraison. Supply is
affected primarily by total light interception.
Since light interception
depends on leaf area, more shoots will
lead to more rapid canopy development
and an earlier peak in canopy
photosynthesis (Figure 3).
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