Photosynthesis:
Grapevines, like other green plants, produce energy in the form of sugars and other compounds through photosynthesis. Water and carbon dioxide are combined in the chloroplasts to produce sugars and starch using energy from sunlight. The rate of photosynthesis is influenced by various factors:
- Light – A leaf exposed directly to the sun can ideally absorb 90% of the sun’s radiation. As light intensity increases so does photosynthesis.
- Temperature – The ideal temperature for photosynthesis is between 70 and 85 F (20 and 30 C). Photosynthesis slows when temperatures are below 50F or above 95F.
- Water – Water influences the opening and closing of the stomata which affects the entry of carbon dioxide into the leaves. If water is limited there is a rapid decline in photosynthesis.
- Leaf Age – The rate of photosynthesis increases as a young grapevine develops and declines as it gets older.
Translocation:
Translocation is the process by which sugar and other compounds are moved throughout the vine.
Transpiration:
Water from the roots of the vine is expired through stomata on the undersides of the leaves through a process known as transpiration (analogous to perspiration). Stomata open during the day and close at night, thus controlling the amount of transpiration that occurs. Hot or windy conditions can cause the stomata to close during the day. Transpiration is influenced by the following factors:
- Humidity – Transpiration decreases as humidity increases.
- Temperature – A rise in temperature increases transpiration.
- Wind – Winds can cause the closure of stomata (reducing photosynthesis and transpiration).
- Water content of soil – During daylight, water is often transpired at a greater rate than it is absorbed from the soil. At night this is reversed.
Respiration:
Respiration is the process by which sugars and oxygen along with other compounds interact and produce energy along with water and CO2. During respiration, energy stored by the vine is released. In some respects respiration can be considered the reverse of photosynthesis. Respiration can be considered to perform two functions: supplying energy for growth and supplying energy for organ maintenance.