UV and Insect eyesUV and Insect eyes

LIGHT&

PHOTOSYNTHESISPHOTOSYNTHESIS

SpectrumSpectrum

Fate of intercepted Fate of intercepted light?light?

Reflect

Transmit

Absorb

Fate of leaf intercepted light?Fate of leaf intercepted light? Reflect - (6-12% PAR, 70% infrared, 3% UV) Degree of reflection varies with type of leaf

surface Transmit - average 10-20% (primarily green and

far red) What would influence this? thickness and structure of leaf Absorb – What does this depend upon?

Fig. 5.4Fig. 5.4

AbsorptionAbsorption

What determines how much light a plant or a group of plants will intercept?

Quantity and position of leaves

Leaf area indexLeaf area index

Leaf Area IndexLAI

Interpretation of LAI see fig 5.5 (d) pg 47 (m2 leaf area/m2 ground area)

LAI 3 means 3m2 leaf area over each m2 of ground

LAIs of different canopy typesLAIs of different canopy types

Summer Temperate Deciduous Forest: LAI 3-5 (1-5% light hitting canopy reaches floor)

Summer Pine Forest LAI 2-4 (10-15% light hitting canopy reaches floor)

Tropical Rain ForestLAI 6-10 (.25 – 2% light reaches floor)

Light levels and LAILight levels and LAI

Why is the amount of light reaching the forest floor of the pine forest greater than that of the deciduous forest?

Does the LAI of an area change throughout the year?

What are the consequences of this for plants of the forest floor?

Light LevelsLight Levels

Are there other factors other than LAI and leaf angle that would influence the amount of light a forest floor organism might receive?

See Fig. 5.7 page 49

Light levels: year profileLight levels: year profile

Photosynthetic Terms

PAR – photosynthetically active radiation

Light compensation point (LCP) Light saturation point (LSP) photoinhibition

PS terms expandedPS terms expanded Light compensation point: rate of

C02 uptake in PS = rate of C02 loss in Respiration

Short version rate of PS = rate of respiration

Light Saturation Point – Point at which increasing light does not increase PS

Photoinhibition - High light levels inhibit PS

LCPLCP

Shade –tolerantShade –tolerant Low PS rates Low respiration rates Low metabolic rates Low growth rates

Shade -intolerantShade -intolerant Higher PS rates Higher respiratory rates Higher growth rates Lower survival in shade conditions

Shade and Shade and SeedlingsSeedlings

Apply your SmartsApply your Smarts How does the concentration of

Rubisco relate to photosynthesis rate?

What does the production of Rubisco have to do with respiration?

What do respiration rates have to do with tolerance to shade?

Apply your SmartsApply your Smarts What do respiration rates have to do

with the light compensation point? What does the light compensation

point have to do with shade tolerance or intolerance?

In general what types of plants would you expect to have a lower light saturation point: shade inotlerant or shade tolerant Why?

Apply your SmartsApply your Smarts What would you change in a plant

that would increase or lower the light compensation point?

Plant a shade intolerant plant in the shade. What would the plant do to compensate for being in low light?

Leafs and LightLeafs and Light

How does the amount of light a leaf receives influence its shape and sizE?

See page 52 And what does surface area and

volume have to do with it?

Shade-Sun leafShade-Sun leaf

PS and TemperaturePS and Temperature See page 59 Fig. 6.3-6.4

PS and TemperaturePS and Temperature

PS and PS and temptemp

Plants and Plants and TemperatureTemperature

Heat gain and loss – What are the parameters?

Reflectivity of leaf and bark Orientation of leaves to sun and

wind? Size and shape of leaves Frost

hardiness – Transpiration cooooooling………

Plants and Plants and TemperatureTemperature

Frost hardiness – mostly genetic Addition of protective compounds

(antifreeze type) allows super cooling

Ice forms in the cell wall????

Transpiration cooooooling………

Temperature and plantsTemperature and plants

Photosynthesis

Light Absorption

PS Activity Problem PS Activity Problem

Relative PS activity

100%

0%

Wavelength400 500 600 700

Light ProblemLight Problem

Relative Absorbency

100%

0%

Wavelength (nm)400 500 600 700

A B C D

PhotosynthesisPhotosynthesis

6CO2 + 12 H20 ---> C6H12O6 + 6H20 + 602

OR6CO2 + 6 H20 ---> C6H12O6 + 602

PS ProblemPS Problem

If you put a plant in a closed container with an atmosphere of 14C02, and H2

180 where would you find the radioactive carbon and the heavy oxygen (180) in the container and/or plant?

Fates of reactantsFates of reactants

C02

H20

C6H1206

02

H20

H20

Movement of waterMovement of water