Water Flashcards
How much water does a vine generally need in cool climates?
minimum 500mm of rainfall per year
How much water does a vine generally need in warm climates?
minimum 750mm of rainfall per year
For what 5 purposes does a vine need water?
- Turgidity (so that it doesn’t wilt)
- Photosynthesis
- Regulating its temperature
- Solvent for nutrients in the soil
- Medium in which all of the vine’s biochemical and physiological mechanisms take place
What is transpiration?
- water vapor diffuses out of the stomata on the underside of the leaves
- the loss of water from the cells in the leaf causes water to be pulled upwards from the soil, through the roots and the above-ground parts of the vine
If a vine has sufficient water, what do the stomata do?
- stomata stay open all day
- open stomata allow the free exchange of water vapor out of the vine, and also let carbon dioxide and oxygen diffuse in and out of the leaves
Describe how water stress occurs. If a vine doesn’t have sufficient water, what do the stomata do?
- stomata partially close
- can help conserve water
- reduces or even stops photosynthesis due to lack of carbon dioxide entering the leaves
What can water stress lead to for the vine?
- stunted growth
- ripening slowed
- leaf loss (extreme)
- vine death (extreme)
Name 4 winemaking regions where the lack of rainfall in the growing season is a large issue. How is it combatted?
- Argentina, California, South Africa and Australia
- irrigation
If water is too easily available into late spring and early summer, what can happen to the vine?
- vegetative growth (of shoots and leaves) is promoted and prolonged into the period of grape ripening, which acts as a competitive source for the vine’s sugars, delaying and compromising ripening
- excessive shading of the grape bunches
When is mild water stress beneficial? Why?
- just before veraison
- it inhibits further vegetative growth
Name 4 reasons why excessive shading of the grape bunches can be harmful.
- reduced formation of anthocyanins, tannins, and aroma compounds
- less tannin polymerization
- higher levels of methoxypyrazines
- poor ventilation (fungal disease risk)
Late in the ripening period, why can excessive water be harmful?
- dilution of sugars in the grapes
- grape splitting (encourages botrytis)
Why can a water deficit late in ripening be harmful?
- grape shrivel
- grapes may not reach desired level of ripeness
Why can damp soils be harmful?
- often cold, especially early in the growing season
- can delay budburst (shorter growing season)
Why can warm soils be beneficial?
- promote budburst
- encourage root growth