ven2lec9_(pnrdh20rel)

ven2lec9_(pnrdh20rel) - VEN 2 Photosynthesis Respiration...

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VEN 2 Photosynthesis , Respiration and Water Relations
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Photosynthesis (Pn) Production of sugars within green tissues in the presence of light Process responsible for all fossil fuels used today Responsible for most if not all O 2 in the atmosphere Amount of sugar produced world-wide via Pn is equivalent to 7.1 tons per person on earth
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Photosynthesis Equation nCO 2 + 2nH 2 O (CH 2 O)n + nO 2 + nH 2 Chlorophyll Light
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Regulation of Photosynthesis Internal Environmental Cultural Practices Biotic factors
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Internal Regulation of Photosynthesis Stomatal conductance Leaf age Mineral nutrient status Vine water status (to be discussed with cultural practices control)
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Stomata are closed in the dark and open in the light
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Internal Regulation of Photosynthesis Stomatal conductance Stomatal conductance is a measure of the pore size. The loss of H 2 O vapor through the stomata is called - Transpiration
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Stomatal conductance (g s ) Relationship of g s to light level. Full sunlight is ~ 2,000 μmol m -2 s -1 (photons) Note – x axis max is only 1500 Internal Regulation of Photosynthesis
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Stomatal conductance (g s ) Relationship of Pn to g s . Pn is linearly related to g s from 0 to ~ 300 mmol H 2 O m -2 s -1 Internal Regulation of Photosynthesis
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Stomatal conductance (g s ) Relationship of Pn to g s . Note – Pn is max at g s values of ~ 450 mmol H 2 O m -2 s -1 . Internal Regulation of Photosynthesis
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Leaf age Relationship of Pn to leaf position on a grapevine shoot. Max Pn occurs at full leaf expansion. As the leaf gets older Pn will decrease slowly Values on right are in μmol CO 2 m -2 s - 1 Internal Regulation of Photosynthesis 13.0 16.1 16.9 16.2 15.7 14.0 9.1 7.4 3.9 0.2 -2.1
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Mineral nutrient status (K) Stomatal opening is controlled by the movement of K + Internal Regulation of Photosynthesis
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Mineral nutrient status (N) Relationship of Pn to N within the leaf. This relationship holds true whether N decreases due to leaf senescence or leaf feeding by insects. Internal Regulation of Photosynthesis
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Regulation of Photosynthesis Environmental factors Light Temperature Water Wind Carbon dioxide Air pollutants
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Regulation of Photosynthesis: Environmental factors Light ( Solar radiation ) Single most important environmental factor. Single leaf Pn not saturated until 2/3 of full sunlight. Whole vine Pn is probably not saturated at all during the day (due to mutual shading of the leaves).
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Light Light compensation point (no net uptake of CO 2 ) is ~ 15 μmol m -2 s -1 . Single leaf light saturation of Pn is ~ 2/3 of full sunlight. Regulation of Photosynthesis: Environmental factors
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Comparison of single leaf Pn and whole vine Pn on a diurnal basis.
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