Transformation of Energy by Plants. Efficiency - How well do plants utilize the solar input?...
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Transcript of Transformation of Energy by Plants. Efficiency - How well do plants utilize the solar input?...
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
LAI
Leaf Area
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
0
5
10
15
20
25
30
35
% light/branch
LAI
EarlysuccessionMidSuccessionLateSuccession
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
Choke Cherry
Northern Red Oak
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
220-260 100-150
Effect of O2 Inhibitory(photorespiration)
None in range 2-21kPa
Temp. response 20º-40º C Usually slight Strong
Water use efficiency Low High
C3
C4
CAM
Mesophyll cell
Mesophyll cell
Mesophyll cell
Bundle sheath cell
Larch (Larix)
N. Amer. Larch distribution
LarchLarch
Red Maple
Black Spruce Light
absorption & height/radius ratio