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Plant Environment: Light. Plants convert light energy into chemical energy. Light. photosynthesis. 6H 2 O+6CO 2 +light --> C 6 H 12 O 6 + 6O 2. Photosynthesis provides plant with energy for growth. Effects of light on plants important in horticulture. Pigment formation.

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Plant Environment: Light

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plant environment light
Plant Environment: Light
  • Plants convert light energy into chemical energy
  • Light
  • photosynthesis
  • 6H2O+6CO2+light --> C6H12O6 + 6O2
  • Photosynthesis provides plant with energy for growth
  • Effects of light on plants important in horticulture
plant environment light2

Pigment formation

Plant Environment: Light
  • Growth rates and habits
  • Light influences...
  • Flowering and fruiting
  • Seed germination
  • Onset of dormancy
plant environment light3
Plant Environment: Light
  • Quality (color of light)
  • Light made up of different colors: R,O,Y,G,B,I,V
  • 3 characteristics of light important to plants:
  • Chlorophyll (main pigment that captures light in plants) absorbs red and blue light
  • Accessory pigments capture different colors
  • Quantity (amount of light)
  • Photoperiod (duration of light)
plant environment light4
Plant Environment: Light
  • Spacing of plants
  • Must prevent shading of neighboring plants
  • Quality and quantity of light influences:
  • Orientation of plants
  • Taller plants to north and shorter plants to south to prevent shading
  • e.g. squash and bean at south end of garden, corn to north
  • Pruning strategies
  • Fruit trees often pruned to remove middle branches; admit more light to center of tree
  • Hedges pruned so that base wider than top to prevent shading
plant environment light5
Plant Environment: Light
  • Etiolation of plants
  • Light necessary for chlorophyll formation in most angiosperms
  • Quality and quantity of light influences:
  • Plants moved to location without light become blanched
  • Blanching applied to several vegetables: cauliflower, celery, scallions
  • Potatoes should be covered completely to prevent production of chlorophyll; produces green spots
  • Etiolation = development of plant in absence of light
  • Whitish stems and leaves, elongated internodes
  • Etiolation useful for cuttings; etiolated stems produce adventitious roots better (light inhibits rooting hormones)
plant environment light6
Plant Environment: Light
  • Etiolation of plants
  • Quality and quantity of light influences:
plant environment light7
Plant Environment: Light
  • Pigment production
  • Chlorophyll breaks down when exposed to light
  • Quality and quantity of light influences:
  • Carotenoids (yellow-red accessory pigments) protect chlorophyll from photodestruction
  • Normally chlorophyll masks carotenoids; destruction of chlorophyll results in yellowing of leaves (=chlorosis)
  • Chlorosis also results from diseases and nutrient deficiencies (N, Mg, Fe, and other nutrients used to produce chlorophyll)
  • Leaves turn color in fall because chlorophyll destruction unmasks carotenoids (tannins present produce browns)
  • red leaves in some plants indicates high levels of carotenoids
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Plant Environment: Light
  • Seed dormancy
  • Photoblastic = seeds influenced by light
  • Quality and quantity of light influences:
  • Positive or negative photoblastic
  • Many weeds are positive photoblastic; tilling soil brings weeds seeds to surface and breaks dormancy
  • Potato tubers are positive photoblastic (store in cool dark place)
  • Some seeds require darkness to germinate (e.g. tomato)
plant environment light9
Plant Environment: Light
  • Branching and stem elongation
  • Red light results in plants with short internodes and vigorous axillary growth
  • Quality and quantity of light influences:
  • Fluorescent lights high in red light
  • Incandescent lights have little red light; plants grown beneath them show etiolation
  • Plants growing below tall plants get little red light (absorbed by leaves of tall plants) and have internode elongation
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Plant Environment: Light
  • Anthocyanin production
  • High levels of light promotes anthocyanins (red pigment)
  • Quality and quantity of light influences:
  • Brightest fall leaves often on trees in full sun
  • Rain causes leaching of anthocyanins; dry falls produce most vivid colors
  • Many fruits produce anthocyanins while ripening; apples redder on outside of tree where exposed to more light
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Plant Environment: Light
  • Photoperiod = response to changes in day length
  • Day length often triggers flowering
  • Effects of photoperiod on plants:
  • Day-neutral plants: plants that flower regardless of day length (e.g. dandelions, many houseplants)
  • Long-day plants: plants that flower when exposed to long day length (short nights)
  • Spinach not planted in midsummer because it will bolt (flower)
  • Short-day plants: plants that flower as day length shortens (e.g. tomato)
  • Flowering can be prevented by extending day length with artificial light or by night interruption
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Plant Environment: Light
  • Shorter day length promotes formation of storage organs
  • Effects of photoperiod on plants:
  • Short days stimulates formation of tubers and bulbs (modified stems) and tuberous roots (modified roots)
  • Strawberry and spider plant stolons produced in presence of long day length
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Plant Environment: Light
  • Sudden change in lighting can cause damage to plants
  • Annual flowers grown indoors need slow acclimatization to more intense sunlight outside
  • Acclimation to light
  • Tropical plants grown outdoors must be acclimatized to low light in offices and homes
  • Weeping figs particularly sensitive to changes in light; will drop all leaves