# Light & Photosynthesis or “You light up my life” A/H 100G J.G. Mexal.

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Light & Photosynthesis or “You light up my life” A/H 100G J.G. Mexal

Light and Photobiology Plant Growth is a Function of Environment

Light and Photobiology Where does all the sunlight go?

Light & Photosynthesis Light: What’s important? Quality (what color) Quantity (how much) Duration (how long)

Light Quality The radiant energy given off by the sun is measured on the basis of wavelengths. The range of wavelengths is placed on the electromagnetic spectrum. Visible light, which drives photosynthesis, is a small segment of all the radiant energy

Light and Photobiology Important Wavelengths Visible spectrum= 380 - 760 nm Photophysiology=280 - 800 nm PAR=400 - 700 nm UV-A (sunscreen)= 320 - 420 nm UV-B (ozone layer)=290 - 320 nm

Light & Photosynthesis Electromagnetic Spectrum nanometers Energy (kcal/cm Wavelength (nm)

Light and Photobiology Conversions 1 nm= 10 -9 m = 10 -7 cm = 10 -6 mm = 10 -3  (microns or micrometers)

Light and Photobiology Solar Radiant Energy BlueGreenOrangeRedFR wavelengths

Light and Photobiology Atmospheric Filters (O 3, CO 2, H 2 O) (nanometers) UV InfraRed

Light and Photobiology Energy Spectra Absorbed by Plants

Light Quantity The intensity of the sunlight varies with the season. Sunlight is typically most intense in the summer and least intense in the winter. The greater the intensity, up to a saturation point, the greater the production of food through photosynthesis.

Light Measurement Units Photometric –1 lux = 1 lumen/m 2 –1 fc= 1 lumen/ft 2 –1 fc = 10.76 lux Radiometric –watts/m 2 Photon (Quantum) Flux –µmol/m 2 /s Full Sun = –10,000 fc –1,000 watts/m 2 –2,000 µmol/m 2 /s

Photosynthesis Intensity vs Crop Plants CropShade- only Shade- mostly Slight Shade Sun-mostly <1,000 fc1-2,000 fc2-8,000 fc3-8,000fc Trees --Coffee tea Apple, pear, plum Banana, pecan Veges Ginseng, tobacco VanillaCabbage, potato Chile, cereals, cotton Flowers PhilodendronVincaForsythiaMums, roses

Light and Photobiology “Red Shift” in Leaves

Light and Photobiology Light Attenuation in a Forest and Meadow Light reaching ground Reflected Light

Light and Photobiology Light Attenuation within a Tree Canopy

Photosynthesis Lighting for House Plants West Summer pm (4000 fc) Winter pm (2000 fc) East Summer am (3000 fc) Winter am (1500 fc) South: Summer noon (6000 fc) Winter noon (4000 fc) North: Summer noon (600 fc) Winter noon (250 fc) Light Requirement: Low Medium High

Light Duration III. Light duration is the length of time plants are exposed to sunlight or darkness. The period of exposure is termed, photoperiod..

Light and Photobiology Daylength Curves Around the World 50 O N Vancouver 42 O Chicago 24-26 O N Miami 10 O Luanda 30 O S Durban 40 O S Cook Strait Day length

Light and Photobiology Important Dates-- for Druids and Plants Equinox –VernalMarch 23 –AutumnalSeptember 23 Solstice –SummerJune 23 –WinterDecember 23

Photoperiodic Response long-day plants: winter barley, red clover, oats, spinach, and winter wheat. short-day plants: soybean chrysanthemums, and poinsettia. day-neutral plants: corn, grapes, peas, and tomatoes

Light and Photobiology Phytochrome--Flowering of Soybean

How does a plant ‘see’ light?

Light and Photobiology Plant Photoreceptors (Pigments)

Light and Photobiology Light-Controlled Plant Processes Germination: light requiring seeds inhibited by FR light Hypocotyl unfolding: requires R or FR light Stem extension: R inhibits; FR promotes Stem movement: B promotes Leaf expansion: prolonged exposure Leaf movement: B & R promotes Flower induction: short-day plants--R inhibits Bud dormancy: induced by FR, delayed by R

Light and Photobiology Light-Controlled Plant Processes

Light and Photobiology Phytochrome -- Photoperiodism Flowering –Short-day plants-- mums, poinsettia –Long-day plants-- spinach Formation of storage organs-- begonia Stem elongation-- strawberry, spider plant Dormancy of woody plants

Light and Photobiology Phytochrome Reaction P R P FR Processes: –Shade detectionIntensity –DormancyClock –FloweringClock 660 nm 730 nm Biological action Destruction (w/o light) Dark reversion

Light and Photobiology Cryptochrome Reaction –involves blue light Process –variable and vague?

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