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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 l.jpg
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


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Plant Environment: Light

  • Growth rates and habits

  • Light influences...

  • Flowering and fruiting

  • Seed germination

  • Onset of dormancy


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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)


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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


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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)


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Plant Environment: Light

  • Etiolation of plants

  • Quality and quantity of light influences:


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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)


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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


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