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

plants re-radiate green light in longer waves long waves do not have as much energy as the short waves

longer waves do not have enough energy to escape from the house result is heat

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 NM cell elongation photosynthesis - chlorophyll absorbs red and blue light

phototropism - plant tends to grow or bend toward a light source

Red photosynthesis stimulates branching encourage growth of axillary buds

phytochrome - light absorbing pigment seed germination in photoblastic seeds

flowering responses photoperiod

Far Red

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

sun loving low light, pale color new leaves are small lack vigor

dont 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

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

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

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 its 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

cyclic lighting from 10 p.m. to 2 a.m. lights on for 6 minutes and off for 24 minutes