LIGHT

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CHAPTER 11

• LIGHT TEMPERATURE

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PHOTOSYNTHESIS
CO2 H2O Light Energy C6H12O6 O2

• Complex Carbohydrates
• Proteins
• Fats

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Light Dark Reactions of PSN

• Light Rx
• 1. H20 2H O
• 2. NADPH NADPH2
• 3. ADP ATP

• Dark Rx
• CO2
• NADPH2
• ATP
• C6H12O6

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Light Quality

• Visible Wavelength
• Visible light is between 400 - 700 nm
• Wavelength vs. Energy
• Shorter Lower
• Longer Higher

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Light Quality

• Visible Wavelength
• Visible light is between 400 - 700 nm
• Wavelength vs. Energy
• Shorter Lower
• Longer Higher

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Light Quality
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Photosynthesis Uses Mostly

• Blue and Red light (reflects green)
• Blue light alone causes compact plants with dark
  green leaves
• Red light alone causes long internodes and light
  green leaves

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Light Intensity

• 3,000 fc will saturate most greenhouse plants
  (higher light needed to to get 3000 fc into plant
  canopy)
• 10,000 fc will saturate most C4 plants

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Maximizing Light Intensity

• Metal framework
• Wider frame spacing
• Paint wooden frames white
• Choice of covering material
• Clean glass
• Wider plant spacing

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Supplemental Lighting

• To increase light intensity
• To control photoperiod

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Types of Lights

• Incandescent
• High heat, low efficiency, high red, low blue
• Fluorescent
• Expensive, less heat, low power, high blue
• HID
• Similar spectrum to fluorescent, more intense

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Photoperiod

• Response of a plant to the day/night cycle
• Can measure a difference of 5 min in 24 hrs.
• Controls
• Bolting in lettuce
• Bulbing in onions
• Tuber formation in dahlia
• Poinsettia bract coloration
• Flowering in Mum
• Etc., etc., etc.

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Did you see a commonality among the examples on
the previous slide???

• Reproduction

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Plant Categories

• Short-day plants
• Long-day plants
• Day-neutral plants

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Short Day Plants(long night plants)

• Typically initiate reproductive behavior when
  daylength drops below 12 hours

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Long Day Plants(short night plants)

• Typically initiate reproductive behavior when
  daylength exceeds 12 hours

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Modifying Daylength

• To create a short day / long night
• Example Poinsettias
• Use black-out cloth (note a flashlight provides
  enough light intensity to create a short night)
• To create a long day / short night
• Example for vegetative growth on young mums
• Turn on light for a few hours in middle of night

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Temperature

• Enzymatic reactions double with each 10oC (18oF)
  rise in temperature
• What does this mean?
• All plant processes including anabolic and
  catabolic reactions move more rapidly at elevated
  temperatures

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Temperature Effects OnNet Plant Growth

• When rate of photosynthesis exceeds the rate of
  respiration, net growth occurs
• When rate of photosynthesis equals the rate of
  respiration, no growth occurs
• When rate of photosynthesis is less than the rate
  of respiration, plant vigor declines
• (Cooler nights are used to reduce the rate of
  respiration to ensure net plant growth)

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Day/NightTemperature Differences

• The magnitude of the difference in day and night
  temperatures can affect
• Growth rate
• Flowering
• Plant nutrition