UV and Insect eyes
LIGHT
&
PHOTOSYNTHESIS
Spectrum
Fate of intercepted light?

Reflect

Transmit

Absorb
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. 5.4
Absorption

What determines how much light a plant
or a group of plants will intercept?

Quantity and position of leaves
Leaf area index
Leaf Area Index
LAI
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 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 Forest
LAI 6-10 (.25 – 2% light reaches floor)
Light 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 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 profile
Photosynthetic Terms
PAR – photosynthetically active
radiation
 Light compensation point (LCP)
 Light saturation point (LSP)
 photoinhibition

PS 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

LCP
Shade –tolerant
Low PS rates
 Low respiration rates
 Low metabolic rates
 Low growth rates

Shade -intolerant
Higher PS rates
 Higher respiratory rates
 Higher growth rates
 Lower survival in shade conditions

Shade and
Seedlings
Apply 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 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 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 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 leaf
PS and Temperature

See page 59 Fig. 6.3-6.4
PS and Temperature
PS and
temp
Plants and Temperature
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 Temperature
Frost hardiness – mostly genetic
 Addition of protective compounds
(antifreeze type) allows super cooling
 Ice forms in the cell wall????


Transpiration cooooooling………
Temperature and plants
Photosynthesis
Light Absorption
PS Activity Problem
100%
Relative
PS activity
0%
400
500
600
Wavelength
700
Light Problem
A
B
C
D
100%
Relative
Absorbency
0%
400
500
600
700
Wavelength (nm)
Photosynthesis
6CO2 + 12 H20 ---> C6H12O6 + 6H20 + 602
OR
6CO2 + 6 H20 ---> C6H12O6 + 602
PS Problem

If you put a plant in a closed container
with an atmosphere of 14C02, and H2180
where would you find the radioactive
carbon and the heavy oxygen (180) in
the container and/or plant?
Fates of reactants
H 20
C6H1206
02
H20
H 20
C02
Movement of water