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Objectives Learn about light as a form of radiation Review the plant growth processes that relate to light Study the characterisitics of light that are.

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Presentation on theme: "Objectives Learn about light as a form of radiation Review the plant growth processes that relate to light Study the characterisitics of light that are."— Presentation transcript:

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2 Objectives Learn about light as a form of radiation Review the plant growth processes that relate to light Study the characterisitics of light that are relevant to horticulturists Consider ways horticulturists manipulate light to meet horticultural goals

3 What is light? But, it is only a small (visible) part of a huge electromagnetic spectrum Infrared RadioUltra-violetX-rays Gamma rays Electromagnetic Spectrum short waveslong waves high energylow energy Microwaves

4 What is light? Visible Spectrum Nanometers of wavelength Nanometer = meters

5 Radiation that Strikes an Object Incoming Radiation (from sun or lamp) Transmission through Reflection off & back Absorption

6 Radiation that Strikes an Object Incoming Radiation (from sun or lamp) Transmission through Reflection off & back Absorption Glass pane (greenhouse)

7 Explains Greenhouse Effect 1. Transmission of radiation through glass Shorter wavelengths only 2. Absorption by objects in greenhouse 3. Objects in greenhouse heat up 4. Objects re-radiate as heat long wavelengths only 5. Long waves cannot get back out through glass - heat trapped in greenhouse

8 Greenhouse Effect Transmission Absorption Re-radiation (heat) Heat (long waves) cant pass through glass - heat is trapped and builds up

9 Greenhouse Effect - Global Absorption by Earth Transmission through atmosphere Re-radiation (heat) Heat (long waves) cant pass through atmosphere (CO 2 & water vapor) - heat is trapped and builds up

10 Lights Characteristics Spectral quality (color or wavelength) Intensity (no. of photons, amt. of energy) Duration (length of lighted period, i.e. day) Direction (angle of incidence)

11 SPECTRAL QUALITY (Kind) Visible Spectrum Nanometers of wavelength

12 Photosynthesis In photosynthesis, all lights colors, or parts of the visible spectrum are not equal! Only some light is absorbed by chlorophyll and other pigments in photosynthesis The absorbed part of the spectrum is called PAR P hotosynthetically A ctive R adiation

13 Incoming Radiation (from sun or lamp) Transmission through Reflection off & back Absorption

14 P A R Nanometers of wavelength Absorption of chorophyll a & b These wavelengths are either reflected off or transmitted through the leaf

15 LIGHT INTENSITY (Quantity) Intensity is measured as micro moles / square meter / second ( mols/m 2 /sec) Sunlight ranges between mols/m 2 /sec Interiors as low as 50 mols/m 2 /sec

16 Plants & Light Intensity CO 2 Uptake (photosynthesis) respiration dark bright light CO 2 Release (respiration) photosynthesis Increasing Light Intensity

17 Plants & Light Intensity CO 2 Uptake (photosynthesis) respiration dark bright light CO 2 Release (respiration) photosynthesis Increasing Light Intensity Compensation Point

18 Compensation Point At this light intensity, a plant captures as much energy through photosynthesis as it needs to survive At the compensation point, a plant will not grow, but it will not die (maintenance level) Below the C.P., a plant will die Above the C.P., a plant may grow

19 Plants & Light Intensity CO 2 Uptake (photosynthesis) respiration dark bright light CO 2 Release (respiration) photosynthesis Increasing Light Intensity Compensation Point Plant Dies Plant May Grow Maintenance

20 Plants & Light Intensity CO 2 Uptake (photosynthesis) respiration dark bright light CO 2 Release (respiration) photosynthesis Increasing Light Intensity Saturation Point

21 At this light intensity, a plant captures the maximum amount of energy through photosynthesis that it is able to do At lower light intensities, a plant will respond (grow faster) to brighter light Above the S. P., brighter light has no effect on growth

22 Plants & Light Intensity CO 2 Uptake (photosynthesis) respiration dark bright light CO 2 Release (respiration) photosynthesis Increasing Light Intensity Saturation Point Grows Faster No Increase

23 C. P. & S. P. Compensation Point & Saturation Point vary with species Sun-loving species tend to have a higher saturation point (make more efficient use of brightly lighted conditions) Shade-loving species tend to have a lower compensation point (survive at lower light intensities)

24 Sun or Shade Plant? CO 2 Uptake (photosynthesis) dark bright light CO 2 Release (respiration) Increasing Light Intensity Sun-loving species Shade-loving species

25 DURATION (How Long?) Plant growth rate and productivity is dependent upon: how much time the plant receives PAR above the compensation point, and how far above the C. P. it is

26 Horticultural Practices Plant spacing - light exposure Pruning - allow light penetration into tree or shrub canopy Eliminate weeds that compete for light Reduce weeds by dense crop canopy (shade out the weeds) Supplemental lighting (interiors/greenhouse)

27 Summary Light is a critical aspect of the environment for plant growth The characteristics of light impact many plant developmental processes

28 Photobiology "Photobiology is broadly defined to include all biological phenomena involving non-ionizing radiation. It is recognized that photobiological responses are the result of chemical and/or physical changes induced in biological systems by non-ionizing radiation. (Constitution of the American Society for Photobiology)

29 Photobiology - Areas Photosensitization - Chlorophylls UV Radiation effects – DNA mutations Environmental photobiology – Plant Productivity Non-visual photoperception – Circadian, photoperiodism Photomorphogenesis – Development of organism Phototropism – Plant movement towards light Photosynthesis – conversion of light energy into chemical energy Environmental photobiology – Plant Productivity Photomorphogenesis – Development of organism Phototropism – Plant movement towards light Photosynthesis – conversion of light energy into chemical energy

30 Properties of light Particle - photons Wave

31 Properties of light Particle - photons Photosynthesis – conversion of light energy into chemical energy Carbon capture – Starch production Field physiological disorders Sunburn, Scald Wave Photomorphogenesis – Development of organism Phototropism – Plant movement towards light Photoreceptors – Phytochrome, Cryptochrome, Phototropins etc. CalciumHormones Several – bitter pit, corking etc.

32 Light absorption and emission by chlorophyll

33 Photosynthesis conversion of light energy into chemical energy CO 2 + H 2 O = (CH 2 O) + O 2 An absorption spectrum provides information about the amount of light energy taken up or absorbed by a molecule or substance as a function of the wavelength of the light. An action spectrum is the rate of a physiological activity plotted against wavelength of light. What is the significance of the overlapping absorption and action spectra?

34 Action spectrum compared with an absorption spectrum

35 Photosynthesis T. W. Engelmann Experiment

36 Photosynthesis - initiation

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39 Background: LEF LEF= Linear Electron Flow FD PC PSIIPSI b6fb6f PQ PQH 2 LHC PQ FNR Chloroplast Stroma Thylakoid lumen Aaron Livingston, Ph.D

40 Background: LEF FD PSII PSI b6fb6f PQ LHC FNR Chloroplast Stroma Thylakoid lumen Aaron Livingston, Ph.D

41 Beyond light reaction

42 Importance of LEF to crop production DCMUDCMU ParaquatParaquat


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