1. Leaves

2. Leaves
Directly involved in transfers of energy, carbon, and water between atmosphere and terrestrial ecosystems
Leaves intercept most sunlight before it reaches the ground
Environment around a given leaf varies dramatically from sunlit top to deeply shaded bottom of a dense canopy

3. Why are leaves green?
Chlorophyll, located within each leaf, absorbs light in both the red and blue spectrum of solar radiation, and reflects light in the green spectrum.

4. Spectral Distribution of a Leaf of an Eastern Cottonwood
Visible
Infrared
Absorbance
Reflectance
(upper surface)
Transmittance
Percent
Wave number (cm-1)
Red
Green
Blue
(After
Gates, 1968)

5. Change in Leaf Shape within the northern temperate forests of the U.S.
Pine
Oak
Maple
Low
High
Water Availability
Fig. 6.17
p. 110

6. Leaf Components - Angiosperm
Broad, flat lamina (blade)
Supported by petiole
Cuticle – waxy substance proctecting the surface (waterproof)
Upper epidermis
give the leaf protection against physical and chemical impacts as well as dessication
Palisade parenchyma cells (part of Mesophyll)
most chloroplasts here if different from spongy
Xylem/Phloem
provides carb, water, mineral transport
Major – transport from leaves
Minor – transport to leaves
Stomata & Guard Cells
most important part of leaf – control!
Spongy parenchyma cells (part of Mesophyll)
Chloroplasts located here
Lower epidermis

7. Leaf Components – Gymnosperm (eastern white pine)
Linear or lanceolate (tapering to a point), bifacially flattened
Size & weight of needles vary with position along shoot
Cuticle
heavy – can have considerable wax
Epidermis
Hypodermal sclerenchyma
for support and strength
Stomata & guard cells
Parenchyma
Xylem/phloem
Endodermis
Transfusion tissue
concentrates solutes from transpiration stream and retrieves selected solutes
that are eventually released to the phloem
Resin duct
defense against insects
allelopathic interactions? (prevention of growth
of another species)

8. Transition from Juvenile to Adult
Juvenile (1st year seedling growth)
cotyledons – first leaves develop
Juvenile leaves - often quite different from adult leaves
some have a rapid transition
Mature leaves/needles
Eucalyptus macarthurii
English Ivy

9. Leaf Veins Veins transport of carbohydrates & mineral nutrients
xylem on upper side of leaf
phloem on lower side of leaf
small, minor veins play a major role in collecting
photosynthate from mesophyll cells

10. Stomatal Dynamics Leaves are the principal photosynthetic organs
changes in photosynthetic activity
(climate change? human disturbance?)
WILL alter plant growth

11. Hairs and guard cells with stomata on the lower surface of Coleus sp.
Leaf hair
Guard cells
Epidermis
                           4
Why are most stoma on the lower side of leaves?
Leaf hair
microclimate around leaf
make leaf less attractive to parasites
Turgor pressure is used to control opening and closing of single stoma
guard cells are responsible
depends on light, temperature, RH, CO2 concentration 3

12. Quantity = 100-600 mm-2 of leaf surface
Stomata
Size = m
Quantity = mm-2 of leaf surface
The loss of water can be 50% of evaporation from a free water surface
Generally open during the day & closed at night
Fewer stomata = larger stomata (white ash, white birch)
Exception: oak (large & numerous)
Very dynamic!

13. Stomata Ceanothus gloriosus, CA Banksia marginata, Australia
Nerium oleander,
Mediterranean region
a & b after NOBS (1963)
c originally A. Hoffmann
Incremental changes – like a door (not just open/closed)
Generally, they are open during the day (light is the
primary trigger), and change can be rapid
20s in corn
several minutes in some conifers (Douglas fir)
What happens if a cloud passes overhead?
What happens if the CO2 conc changes?
What if I touch a leaf?
What if the soil dries out?
From: Castri and Mooney, 1973

14. Water Loss in Trees & Adaptations
Most water loss from woody plants is from leaves
Stomata must open for CO2 to diffuse into plant.
As a result of the difference in VP between vegetation
& atmosphere, H2O will diffuse out of the leaves
Wind moves the saturated air away, and the process
continues
Adaptation:
more and larger stomata on bottom of leaves – why?
(at most 1% of leave surface)
pine needles show deeply sunken stomata – why?

15. Regulate stomatal size through turgor pressure
Guard Cell Dynamics
Regulate stomatal size through turgor pressure
Can’t increase in width, but can increase in length
Driven by changes in Osmotic Potential (K+)
Increase in turgor = increase in stomata size!!!!!

16. Role of Potassium (K+) in Stomatal Dynamics
Osmotic potential (define)
As K+ ions move into the guard cell, this increases water movement
into cells as well. This increases the turgor pressure.
As guard cells cannot get wider, only longer, this forces them open.
mechanism not fully understood here
Can be triggered by both roots or leaf water status

17. Water – CO2 Exchange Broad, flat lamina (blade) Supported by petiole
Cuticle – waxy substance protecting the surface (waterproof)
Upper epidermis
give the leaf protection against physical and chemical impacts as well as dessication
Palisade parenchyma cells (part of Mesophyll)
most chloroplasts here if different from spongy
Xylem/Phloem
provides carb, water, mineral transport
Major – transport from leaves
Minor – transport to leaves
Stomata & Guard Cells
most important part of leaf – control!
Spongy parenchyma cells (part of Mesophyll)
Chloroplasts located here
Lower epidermis

18. Stomatal Response to Environment
midnight
noon
time during day
relative average stomatal aperture
time
dark
light
normal
internal
CO2, H2O
low CO2
high H2O stress
increased
CO2
wind or
water
stress
high temperature
higher
irradiance
lower
typical day, typical plant
some plants
cloudy day
very dry soil
succulents

19. Energy, water and CO2 balances over a leaf
Fig. 6.1
p. 95
Convection
Radiation
Solar (short-wave)
radiation
Reflected
Long-wave
Transmitted
Evapotranspiration
Conduction
Internal
CO2
H2O
Water
Use
Efficiency

20. Sun and Shade Leaves - Hemlock
If there is a large change in leaf shape between sun and shade leaves, the
plant is able to adapt to either sun or shade conditions.
But, if there isn’t, then the plant is designed for a specific light availability
(top of canopy, understory) and cannot adjust for big changes
in light availability.

21. Sun and Shade Leaves – Boldina (found in Chile, similar to laurel)
In shade intolerant species, there are fewer stomata per leaf unit as shade increases

22. Sun and Shade Leaves – American beech
leaf
In angiosperms, shaded leaves are thinner, larger, less-deeply lobed
less palisade tissue, less conducting tissue
increases in specific leaf area (amount of leaf area per gram of
dry weight), increasing amount of chlorophyll per
unit dry weight, less per leaf area.
Gymnosperms – shaded leaves
similar response to angiosperms
thinner, higher chlorophyll content,
reduced stomatal frequency
shade
leaf
Fig. 6-12
p. 105

23. Sun and Shade Leaves - Peumo
Anatomical Structure of sun and shade leaves of
Cryptocarya alba
Mean of 50 leaves (After Hurtado, 1969)
Sun leaf
Shade Leaf
Leaf surface area
9.7 cm 2
18.7 cm 2
Leaf thickness
321.7 m
216.8 m
Thickness of upper epidermis
21.0 m
15.2 m
Thickness of lower epidermis
13.5 m
8.0 m
Cuticle thickness, upper
4.8 m
2.7 m
Cuticle thickness, lower
1.5 m
1.1 m
Stomata frequency
690/mm 2
610/mm 2
Contribution of palisade
47%
39%
tissue to mesophyll
From: Castri and Mooney, 1973