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 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
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?