Transcript Energy and Plants

Transformation of Energy by
Plants
Efficiency - How well do
plants utilize the solar input?
•
Ecological (or Lindeman) efficiency
– (GPP/solar radiation)
– wild and cultivated plants ~1.6%.
•
Assimilation efficiency - GPP/light
absorbed
– 8% at full light to 18% in dim light.
Light saturation point
•
Assimilation efficiency - GPP/light
absorbed
– 8% at full light to 18% in dim light.
– Light saturation point
– Bonner hypothesis
– Many temperate leaves:
» Adapted to low light conditions
Chlorophyll concentration
From AJB 92(2) - Jan 05
•
Biochemical efficiency
– molecules of glucose produced/amt. of light
absorbed by the photosystems.
•
Photosynthesis is most often limited by
CO2 concentrations
Solar radiation within the forest
•
PAR is light
at 380-710
nm - about
40% of the
total
irradiation
reaching the
plants
Changes with seasons
Leaf Area Index (LAI)
(Surface area of
leaves over given
area of
ground)/(area of
ground itself)
LAI
Leaf Area
LAI
LAI=4.01
Light attenuation
Typical LAI for deciduous forest = 3 to 5;
for coniferous forest = 2 to 4; tropical rain forest = 6 to 10
Color spectrum
Attenuation of PAR is
dependent on:
•
LAI at a given level above the ground
•
Arrangement of leaves (multi- or
monolayers)
•
Angle at which leaves are held to the
horizontal.
Very little light between 500 and 700 nm gets
through the canopy.
Successional age
•
•
•
Eastern
deciduous trees
# of layers also
declines with
successional age
Data from
Henry Horn
35
30
25
Early
succession
Mid
Succession
Late
Succession
20
15
10
5
0
% light
/branch
LAI
Sunflects
Sunflects
•
Decrease as tree height & LAI increase
•
Short duration (1-30”) normally
•
Varies from 10-85% of daily photon flux
density in a given area
Production
Sunflects
•
Decrease as tree height & LAI increase
•
Short duration (1-30”) normally
•
Varies from 10-85% of daily photon flux
density in a given area
•
Leaf “induction” important for efficiency
•
As duration  efficiency of utilization 
Victoria Lily
Leaf Unit Placement
•
Placed under gaps in upper layer
•
Under upper leaves - can receive light
from three sources:
– Passed through other leaves
– Reflected off other surfaces
– Direct light passing through
Umbra (RDZ)
•
•
•
Shadow cast
by circle
Distance for
influence to
be gone
~70*diameter
– Clear day
– Sun @ zenith
Leaf angle
•
Umbra decreases as a leaf orientation
moves toward vertical
Henry Horn’s hypothesis
•
Trees growing in the open
– leaves arranged in depth in a random
array
– Small leaves; irregular shape
– LAI>1
Open sun plants
Northern Red Oak
Choke Cherry
Henry Horn’s hypothesis
•
Understory trees in dense shade
– Leaves nonrandom; short vertical distance
– Regular shape; larger than leaves in open
– LAI~=<1
•
Single branch of a tree adapted to
growth in the open should cast less
shade than a single branch adapted for
dim light.
Shade plants
Growth Rate
•
•
R=E*F
F is comprised of:
– Ratio of leaf wt. To plant wt. (LWR)
– Ratio of leaf area to leaf weight or specific
leaf area (SLA)
•
•
LWR is fairly steady
SLA can change markedly if plant is
moved from sun to shade
C3 vs. C4 Photosynthesis
Characteristic
C3
C4
Initial CO2 fixing enzyme
RuBP carboxylase
PEP carboxylase
Location of carboxylase
Mesophyll
Bundle sheath
Operating internal CO2
concentration cm3 m-3
Effect of O2
220-260
100-150
Temp. response 20º-40º C
Inhibitory
(photorespiration)
Usually slight
None in range 2-21
kPa
Strong
Water use efficiency
Low
High
C3
Mesophyll cell
Mesophyll cell
C4
Bundle sheath cell
CAM
Mesophyll cell
Larch (Larix)
N. Amer. Larch distribution
Larch
Larch
Red Maple Black Spruce
Light absorption &
height/radius ratio