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

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

What is “light”?But, it is only a small (“visible”) part of a huge electromagnetic spectrum

Infrared RadioUltra-violetX-raysGamma rays

Electromagnetic Spectrum

short waves long waves

high energy low energy

Microwaves

What is “light”?

Visible Spectrum

380 500 560 760650600470430

Nanometers of wavelengthNanometer = 0.000000001 meters

Radiation that Strikes an ObjectIncomingRadiation(from sun orlamp)

Transmissionthrough

Reflectionoff & back

Absorption

Radiation that Strikes an ObjectIncomingRadiation(from sun orlamp)

Transmissionthrough


Absorption

Glass pane(greenhouse)

Explains “Greenhouse Effect”

1. Transmission of radiation through glassShorter wavelengths only

2. Absorption by objects in greenhouse3. Objects in greenhouse heat up4. Objects re-radiate as heat

long wavelengths only

5. Long waves cannot get back out through glass - heat trapped in greenhouse

Transmission

Absorption

Re-radiation (heat)

Heat (long waves)can’t pass throughglass - heat is trappedand builds up

Absorptionby Earth

Transmissionthroughatmosphere Re-radiation

(heat)

Heat (long waves)can’t pass throughatmosphere (CO2 & water vapor) - heat is trapped and builds up

Light’s 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)

Visible Spectrum

500 560 760650600470430

Nanometers of wavelength

Photosynthesis In photosynthesis, all light’s 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

Photosynthetically Active Radiation

IncomingRadiation(from sun orlamp)

Transmissionthrough


Absorption

P A R

380 500 560 760650600470430

Nanometers of wavelength

Ab

sorp

tion

of c

hor

op

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l a &

b

These wavelengths are eitherreflected off or transmittedthrough the leaf

• Intensity is measured as micro moles / square meter / second (mols/m2/sec)

• Sunlight ranges between 1000-2000 mols/m2/sec

• Interiors as low as 50 mols/m2/sec

Plants & Light IntensityC

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respiration

dark bright light

CO

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photosynthesis

Increasing Light Intensity


O2 U

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respiration

dark bright light

CO

2 R

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(re

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photosynthesis


Compensation Point

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


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dark bright light

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photosynthesis


Compensation Point

Plant DiesPlant Dies Plant May GrowPlant May Grow

MaintenanceMaintenance


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dark bright light

CO

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photosynthesis


Saturation Point

Saturation Point• 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


O2 U

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photosynthesis


Saturation Point

Grows FasterGrows Faster No IncreaseNo Increase

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)

“Sun” or “Shade” Plant?C

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dark bright light

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“Sun-loving” species

“Shade-loving” species

• 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

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)

Summary

• Light is a critical aspect of the environment for plant growth

• The characteristics of light impact many plant developmental processes

PhotobiologyPhotobiology

"Photobiology is broadly defined to include all "Photobiology is broadly defined to include all biological phenomena involving non-ionizing biological phenomena involving non-ionizing

radiation. It is recognized that photobiological radiation. It is recognized that photobiological responses are the result of chemical and/or responses are the result of chemical and/or

physical changes induced in biological systems by physical changes induced in biological systems by non-ionizing radiation.”non-ionizing radiation.”

(Constitution of the American Society for (Constitution of the American Society for Photobiology)Photobiology)

Photobiology - AreasPhotosensitization - ChlorophyllsPhotosensitization - Chlorophylls

UV Radiation effects – DNA mutationsUV Radiation effects – DNA mutations

Environmental photobiology – Plant ProductivityEnvironmental photobiology – Plant Productivity

Non-visual photoperception – Circadian, Non-visual photoperception – Circadian, photoperiodismphotoperiodism

Photomorphogenesis – Development of organism Photomorphogenesis – Development of organism

Phototropism – Plant movement towards lightPhototropism – Plant movement towards light

Photosynthesis – conversion of light energy into Photosynthesis – conversion of light energy into chemical energychemical energyEnvironmental photobiology – Plant ProductivityEnvironmental photobiology – Plant Productivity

Photomorphogenesis – Development of organism Photomorphogenesis – Development of organism

Phototropism – Plant movement towards lightPhototropism – Plant movement towards light

Photosynthesis – conversion of light energy into Photosynthesis – conversion of light energy into chemical energychemical energy

Properties of lightProperties of light

Particle - photonsParticle - photons WaveWave

Properties of lightProperties of lightParticle - photonsParticle - photons

Photosynthesis – conversion of Photosynthesis – conversion of light energy into chemical light energy into chemical energyenergy

Carbon capture – Starch productionCarbon capture – Starch production

Field physiological disordersField physiological disorders

Sunburn, ScaldSunburn, Scald

WaveWave

Photomorphogenesis – Photomorphogenesis – Development of organism Development of organism

Phototropism – Plant Phototropism – Plant movement towards lightmovement towards light

Photoreceptors – Phytochrome, Photoreceptors – Phytochrome, Cryptochrome, Phototropins etc. Cryptochrome, Phototropins etc.

CalciumCalcium

HormonesHormones

Several – bitter pit, corking etc. Several – bitter pit, corking etc.

Light absorption and emission by chlorophyll

PhotosynthesisPhotosynthesisconversion of light energy into chemical energyconversion of light energy into chemical energy

COCO22 + H + H22O = (CHO = (CH22O) + OO) + O22An 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?

Action spectrum compared with an absorption spectrum

PhotosynthesisPhotosynthesis

T. W. Engelmann Experiment

Photosynthesis - Photosynthesis - initiationinitiation

Background: LEF

LEF= Linear Electron Flow

FD

PC

PSII PSIb6f

PQ PQ

PQH2 PQH2

LH

C

LH

C

PQ

FNRChloroplast Stroma

Thylakoid lumen

Aaron Livingston, Ph.D

Background: LEF

FD

PSII PSIb6f

PQ

LH

C

LH

C

FNRChloroplast Stroma

Thylakoid lumen Aaron Livingston, Ph.D

Importance of LEF to crop production

DCMU

Paraquat

Documents

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