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Light and Temperature Interaction
Fall Leaf Color• cool temps - very bright days
Orange• yellow, reds, purples and
browns
• chlorophyll cells die as temperatures get cooler
Yellow• carotenoids
• after chlorophyll dies you see the other pigments that are always present
Red-Purple• anthocyanins
• not always present
• synthesized in cooler temps
• made from sugar molecules
Brown• tanins
• mask or show up more once chlorophyll dies
• produced in the leaves
Leaf Fall• need an abscission layer
• leaf can no longer translocate carbohydrates out of the leaf
Bright Days• lots of carbohydrates in the
leaf
• anthocyanins get brighter color
The Key……• cool, short days
Greenhouse Effect• short, high energy wave
lengths of light from sun enters house
• absorbed by structures and plants
Greenhouse Effect• plants re-radiate green light
in longer waves
• long waves do not have as much energy as the short waves
Greenhouse Effect• longer waves do not have
enough energy to escape from the house
• result is heat
Greenhouse Effect• this is how the earth is heated
• long waves cannot escape through the clouds
• cloudy nights are warmer
Light• energy - electromagnetic
radiation
• wavelengths - distance from peak to peak
• measured in nanometers “NM”
Far Red• color plants use
Infra Red• heat energy
Visible light• light quality - color
• quantity - intensity, how bright
• duration - photoperiod
Quality• blue - 400-510 NM
• cell elongation
• photosynthesis - chlorophyll absorbs red and blue light
Quality• phototropism - plant tends to
grow or bend toward a light source
Red• photosynthesis
• stimulates branching
• encourage growth of axillary buds
Red• phytochrome - light
absorbing pigment
• seed germination in photoblastic seeds
Red• flowering responses
• photoperiod
Far Red• filters through leaf• inhibits branchingphytochromereactions - inhibitsgermination ofphotoblastic seeds
Far red• promotes stem elongation
Yellow - Green• does not effect plants
Intensity• measured in foot candles
• amount per unit area on plant
Plants• shade loving
• too much sun - leaf burn
• dehydrate
• kill chlorophyll
Plants• sun loving
• low light, pale color
• new leaves are small
• lack vigor
Plants• don’t flower properly if at all
Light• Light Compensation Point
-”LCP”
• light intensity where rate of photosynthesis = the rate of respiration
LCP• Lowest intensity you can
grow a plat at
• If a plant is grown below this level, respiration will be greater than photosynthesis
LCP• plant will die
• for a plant to grow photosynthesis must be greater than respiration
Acclimitization• preparing plant for lower
light intensity conditions
• expose to lower light intensity
Artificial Lights• Incandescent
• far red, red - elongation
• low blue
• 80% of emitted radiation is heat
Incandescent• 20% visible light
• 12% utilized by plant
Flourescent• red, blue
• 36% heat energy
• 22% light used by plant
• spectral flexibility
Flourescent• can change the quality of the
light by changing the coating on inside of bulbs
• Cool White - Ca Halophosphate
“Gro-Lux”• coated with Mg
Fluorogerminate
• not as long life as cool white, 30X more expensive
Metal Halide• increase light intensity
Low Pressure Sodium• yellow glow
• energy efficient
• yellow - orange light
High Pressure Sodium• red, blue light
• energy efficient
Photoperiod• length or duration of the light
period
• biological measurement of relative length of light and dark periods
Photoperiod• effects
• flowering
• leaf abscision
• dormancy - acclimate for winter
Effects…..• Sex expression
• runner formation
• tuber formation
• bulb formation
Short Day Plants• flower when day length is
shorter
• the dark period is critical
• it’s dark longer than it is light
Short Day Plants• examples
• Chrysanthemum
• Christmas Cactus
• Poinsettia
Long Day Plants• flower when days are long
and nights are short
• example: lettuce, radish, petunias
Facilitative Long Day• flower any period
• if long day - flowering is enhanced
• examples - tomato, begonia
Day Neutral• flower under long or short
day lengths
• example: African Violet
Poinsettias• use night interrupted lighting
• turn on artificial lights from 10 p.m. to 2 a.m.
• splits up the dark period
Poinsettias• cyclic lighting from 10 p.m.
to 2 a.m.
• lights on for 6 minutes and off for 24 minutes