Chapter 9 Photosynthesis: Physiological and ecological considerations

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Chapter 9 PhotosynthesisPhysiological and
ecological considerations

• ? Address the intact leaf under natural
  conditions
• ? The major environmental factors
• directly light, temperature, and ambient
  CO2,
• indirectly humidity, soil moisture
• ? Physiologists, agronomists, and ecologists
• ? Limiting factors for photosynthesis
• the slowest step determine the rate of
  photosynthesis
• Rubisco activity, ribulose bisphosphate
  regeneration, triose phosphate metabolism ? for
  C3 plants
• ? A supply and demand function

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Three light parameters spectral quality,
amount, and direction
Full sunlight, incandescent light, fluorescent
light
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quanta
Systeme International unit, p.200 Under direct
sunlight 2000 ?mole m-2s-1
? 900 Wm-2
watt (W) J/s
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Lux or foot-candles lumen (lm) the
luminous flux on a unit surface, all points of
which are at unit distance from a uniform
point source of one candle. Intensity
was expressed either as foot candles (lm ft-2)
or lux (lm m-2) based on the
perception of light by the human eye, which is
maximally sensitive to light within the green
region of the spectrum, at 555 nm.
Instruments calibration
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Leaf anatomy maximizes light absorption
fluorescence
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About 85 to 90 of PAR is absorbed by leaf
Transparent to visible light and convex
(focus light) at epidermal cells
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Palisade cells light to pass through sieve
effect chlorophyll is confined to the
chloroplasts light channeling through the
central of vacuole and air space between the
cellsSpongy cells light absorption light
scattering increase the travel length
C3
Hairs, salt glands, and epicuticular wax
(reflect light)
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Plant compete for sunlight

• ? A canopy configuration
• ? A rosette growth leaves grow radially
• ? A branching structure increase interception
• ? Sunflceks one of the characteristics of shade
  plants
• capture a short burst of
  sunlight

dandelion
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Solar tracking

• ? The leaf blade is perpendicular to the incident
  light
• ? alfalfa, cotton, soybean, bean, lupine, and
  mallow family
• ? Circadian rhythms sun rise, sun set
  intermittent cloud, night/dawn
• ? a blue-light response of leaf movement
• ? Photosensitive region major leaf veins
• ? Pulvinus is the organ to control the leaf
  orientation, at the junction between the blade
  and petiole
• ? Heliotropism paraheliotropic vs.
  diaheliotropic (short-lived plants)

Lupinus succulentus
????
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Pulvinus at the junction between the blade and
petiole
The mechanism of leaf movement a rapid
response to phytochrome involving ion fluxes
across membranes causes turgor changes ?
pH change also involve
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Plant acclimate and adapt to sun and shade p.
672 If tolerance increases as a result of
exposure to prior stress, the plant is said to
be acclimated (or hardened) ? environmental
A genetically determined level of resistance
acquired by a process of selection over many
generations is adaptation ? genetic p.
203 Glossary
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Photosynthetic responses to light by the intact
leaf

• Light compensation point (LCP) the photon flux
  when photosynthetic CO2 assimilation equal to CO2
  release by mitochondria respiration
• LCP varied with species and developmental
  conditions

The carboxylation capacity of rubisco or the
metabolism of triose phosphates

• A C3 plant

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Light compensation point

• Sun plants
• 1020 µmole m-2 s-1
• Shade plants
• 15 µmole m-2 s-1
• Maximal photosynthetic rate
• sun ? shade plants
• Maximum quantum yield
• the slope (p. 131)

saturation
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Quantum yield No. of photochemical products /
Total No. of quanta absorbed

• Gas solubility/ temp
• C4 plants CO2 concentration
• C3 plants photorespiration
• lower temp, higher
• quantum yield

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Growth conditions affect the photosynthetic
properties of a leaf