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