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Grape Physiology Section 3 Stomata Photosynthesis.

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Presentation on theme: "Grape Physiology Section 3 Stomata Photosynthesis."— Presentation transcript:

1 Grape Physiology Section 3 Stomata Photosynthesis

2 The Aerial Structure Of The Vine A leaf requires between days to become fully expanded The leaves begin to senesce about 4-5 months after unfolding in full sunlight

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5 The Aerial Structure Of The Vine The cuticle Protect the leaf and conserve water

6 The Aerial Structure Of The Vine The pallisade cells consist of one layer of cells containing many chloroplasts The spongy mesophyll cells also contain many chloroplasts and numerous air spaces, to allow gases and water to pass between the cells and the air spaces

7 The Aerial Structure Of The Vine Stomata are small openings in the leaves and are generally found on the underside of the leaf Stomata allow gas and water exchange with the atmosphere

8 The Aerial Structure Of The Vine Figure 3.5: Dicotyledon leaf showing tissue arrangement in cross-section (Source Weaver, (1976)

9 The Aerial Structure Of The Vine

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11 The Aerial Structure Of The Vine Stomata Open and close in response to sunlight and internal CO2 concentration

12 The Aerial Structure Of The Vine Figure 3.7: The Mechanism of Stomatal Opening and Closing (Source: Berg L R. (1997) Introductory Botany. Plants, People and the Environment)

13 The Aerial Structure Of The Vine How Stomata Function Consists of two guard cells and associated cells Open and close in response to photosynthesis Light strikes the leaf, photosynthesis begins and reduces the CO2 concentration within the leaf cells

14 The Aerial Structure Of The Vine Potassium and other solids are transported into the guard cells As potassium increases in the guard cells, water moves into the cells by osmosis The guard cells then open as the cell becomes turgid, the cells become curved, creating an opening

15 The Aerial Structure Of The Vine Stomata close in response to decreasing light (ie reduced photosynthesis) and When water supply is limited (ie reduced turgidity)

16 The Aerial Structure Of The Vine Stomatal closure results in: an increase in leaf temperature an increase in leaf O2 a decrease in leaf CO2 Photosynthesis will decrease and respiration will increase, resulting in a decrease in sugar and carbohydrate production

17 The Aerial Structure Of The Vine 3.4 Photosynthesis

18 The Aerial Structure Of The Vine Photosynthesis Photosynthesis is the process whereby sugars are produced primarily in the leaves of the grapevine

19 Photosynthesis carbon dioxidewater sugar oxygen sunlight

20 The Aerial Structure Of The Vine Environmental Factors affecting Photosynthesis Photosynthesis is fundamental to the vines function, therefore the rate of photosynthesis affects the rate of growth and the crop production The rate of photosynthesis is dependent on many factors

21 The Aerial Structure Of The Vine Sunlight 1. Sunlight Quantity Photosynthesis will not occur between 1-5% full sunlight The stomata are closed preventing CO2 movement into the leaf.

22 The Aerial Structure Of The Vine The amount of sunlight received by the vine depends on many factors including: latitude Season time of day cloud cover the depth of the canopy row orientation

23 The Aerial Structure Of The Vine As the light intensity increases the rate of photosynthesis increases If environmental conditions are optimal and the leaf is in full sunlight then the leaf will photosynthesise at the optimum capacity at one third to one half of full sunlight An increase in light levels will not increase the rate of photosynthesis in that leaf

24 The Aerial Structure Of The Vine The grower can use techniques which increase the sunlight availability to the vines leaves, and therefore increase the vines photosynthetic capacity, increasing the potential yield What are some?

25 The Aerial Structure Of The Vine 2. Sunlight Quality Grapevine leaves strongly absorb light In full sunlight leaves absorb approximately 80% of full light, transmit 10% to the interior and reflect 10% to the atmosphere Therefore a leaf behind the first leaf will only absorb approximately 8% of the original light

26 The Aerial Structure Of The Vine Leaves absorb only part of the colour spectrum of sunlight which is in the visible range from nm wavelength

27 The Aerial Structure Of The Vine As sunlight passes through the canopy, the ratio of light changes, with an increase in other wavelengths compared to the visible wavelengths

28 The Aerial Structure Of The Vine Red light at 660 nm is absorbed by leaves whereas far red light at 730 nm is not As light passes through the canopy the amount of far red increases compared to red light

29 The Aerial Structure Of The Vine This reduces the rate of photosynthesis in leaves deeper in the canopy Shaded leaves have a lower light compensation point than leaves in full sun

30 The Aerial Structure Of The Vine The change in red/far red ratio also affect fruit colour and shoot growth Therefore, leaves need to be well exposed to achieve their potential rate of photosynthesis

31 The Aerial Structure Of The Vine 3. Diffuse light Diffuse light is light reflected from the clouds, soil surface, impurities in the air and other objects Most light reaching the canopy surface is diffuse light

32 The Aerial Structure Of The Vine 4. Sunflecks As the sun moves across the sky and wind moves the leaves, they become illuminated Grapevine leaves are efficient at utilizing sunflecks Experiments have shown that only 1% of the leaf needs to be illuminated for the photosynthetic rate to be greater than the compensation point

33 Figure 3.9: Light Absorption

34 The Aerial Structure Of The Vine Figure 3.10: Angle of light in relation to leaf photosynthesis

35 The Aerial Structure Of The Vine Temperature Photosynthesis involves reactions involving enzymes which are temperature responsive The rate of photosynthesis at temperatures below 20 O C is less than at O C, the optimum

36 The Aerial Structure Of The Vine Figure 3.11: Affect of Temperature on the Rate of Photosynthesis

37 The Aerial Structure Of The Vine Temperature However, O C is not necessarily the optimum temperature for vine development and growth For example, anthocyanin development is greatest at O C rather than at O C

38 The Aerial Structure Of The Vine Above 30 O C, the photosynthetic rate declines and may almost cease at 45 O C Increased temperatures affect enzymes, desiccate tissue and close the stomatal pores, all reducing photosynthesis The rate of respiration is also increased at higher temperatures, therefore net gain of sugars may be reduced. Generally leaves are O C warmer than air temperature

39 The Aerial Structure Of The Vine If there is insufficient water for transpiration then a moisture deficit will result in reduced transpiration increasing the leaf temperature further

40 The Aerial Structure Of The Vine Figure 3.12: Affect of Temperature on Photosynthesis

41 The Aerial Structure Of The Vine Water Availability Water influences photosynthesis in 2 ways It is required as a reactant in the production of sugars It influences stomatal opening

42 The Aerial Structure Of The Vine Therefore water availability does not impact on the photosynthesis reaction itself. The effect of water is greater if evaporative demand exceeds the water supply

43 The Aerial Structure Of The Vine The leaves then become moisture stressed This will cause the stomata to close, due to loss of turgor as water moves out of the guard cells CO 2 levels are then reduced, inside the leaf

44 The Aerial Structure Of The Vine If leaf water status remains low then the leaves will wilt Stomatal reopening is slowed and consequently photosynthesis will be reduced The leaves may take several days to regain their full photosynthesis potential once sufficient water is available

45 The Aerial Structure Of The Vine Carbon Dioxide As the level of carbon dioxide (CO 2 ) increases the rate of photosynthesis also increases This has been shown experimentally using potted vines in controlled environments CO2 concentration in the atmosphere is now around 387 ppm, up from about 280 ppm at the start of the industrial revolution. ▫Intergovernmental Panel on Climate Change predict 400ppm by the end of the century

46 The Aerial Structure Of The Vine At high levels of light the availability of CO 2 may limit the rate of photosynthesis CO 2 will not diffuse into the cells fast enough to replace that used in photosynthesis. If stomata close, for example due to water stress then CO 2 is also limited

47 The Aerial Structure Of The Vine A light wind helps to keep CO 2 levels balanced as a constant supply is near the stomata

48 The Aerial Structure Of The Vine Figure 3.13: Effect of Temperature and CO 2 on Rate of Photosynthesis (Adapted from Winkler, et al (1974))

49 The Aerial Structure Of The Vine Vine Factors affecting Photosynthesis Leaf Age Young rapidly unfolding leaves require carbohydrates Young leaves begin to export carbohydrates when they reach approximately 30% of full size but, they continue to import carbohydrates until they reach 50-75% of their full size

50 The Aerial Structure Of The Vine Figure: 4.12: Effect of Leaf Age on Photosynthesis of Thompson Seedless Vines Net Photosynthesis Leaf Age – days since unfolding

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52 The Aerial Structure Of The Vine Crop Load Sugars produced by photosynthesis are essential for ripening fruit Crop load and canopy size can affect the photosynthesis rate

53 The Aerial Structure Of The Vine If leaves are removed to increase light exposure to fruit, the remaining leaves can increase their photosynthetic rate to compensate, at least partially, for the removed leaves

54 The Aerial Structure Of The Vine However, excessive defoliation will reduce the ability of the vine to produce sufficient sugars to ripen the fruit The practice of fruit thinning is used to balance the crop load to ensure sufficient ripening


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