Download Light and Temp Interaction

Light and Temperature
Interaction
Modified by Georgia Agricultural
Education Curriculum Office
June, 2002
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
• tannins
• 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
auxiliary buds
Red
• phytochrome - light
absorbing pigment
• seed germination in
photoblastic seeds
Red
• flowering responses
• photoperiod
Far Red
• filters through leaf
• inhibits branching
phytochrome
reactions - inhibits
germination of
photoblastic 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 abscission
• 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