Transcript Evergreens How they respond to excessive quantities of light in the

Evergreens and Sunlight
by
Charlie Morriss
Winter Ecology
Spring 2005
Purpose:
 Do
different types of evergreens
respond differently to the excessive
quantities of light in winter?
Review
 Different
species of plants have
developed specific adaptations for
surviving in the winter environment
Primary winter stress factors
 Increased amount of albedo
 Lower overall temperatures
Evergreen vs. Deciduous
 Deciduous
plants lose leaves…
Evergreen plants do not!
Types of Evergreens


Conifers
Douglas fir, Limber pine, Lodgepole
pine, etc.
Broad-leaf
Arctostaphlos uva-ursi
a.k.a. kinnikinnick
Arctostaphylos uva-ursi or
kinnikinnick
Rhododendron albiflorum
Responses to excessive sunlight



Douglas fir experiences complete
downregulation of photosynthesis
Kinnikinnick also experiences complete
downregulation of photosynthesis
The sub-alpine fir experiences
no downregulation if in the sun,
but if in the shade it experiences complete
downregulation
Adaptations for dealing with Sun
Minor processes

Decrease in chlorophyll within leaves and
needles

Alter the angle of the leaf

Align chloroplasts along wall

Reflect light
Adaptations for dealing with Sun
Major processes
Collectively known as
Photoprotection


Release of caratenoid
(xanthophylls)
Degrading of certain proteins
Benefits of the photoprotection
strategy


Minimal cost is far less than that of
forming new leaves
Greater acclimation of light environments
example:
top of the canopy v. forest floor
What about evergreens that are
in the shade?
 Experience
levels
increase in chlorophyll
 Photosynthesis
capacity are
increased or remain the same (as
summer levels)
Results
Are there any photoprotective
differences between broad-leafed
and coniferous evergreens?
Generally the answer is no, but certain
species have made specific adaptations.
Both
types display downregulation of
photosynthesis
Both types use photoprotective
mechanisms to survive
Shaded sites
vs.
Sun-exposed sites
Photoprotective patterns for
both types of evergreens
HABITAT
Sun Exposed
Sites
Shaded Sites
Above-ground
growth
None
None
Photosynthesis
Decreased capacity
Same or increased
capacity
Light collecting
system
Decrease in
chlorophyll levels.
Decrease in D1
protein.
Increase in
chlorophyll levels.
Conclusion
 There
are no major differences in
strategies between the broad-leaf
and coniferous evergreens deal with
excessive sunlight.

Evergreens in the shade exhibit
higher levels of chlorophyll and have
a greater or equal capacity for
photosynthesis than during summer.
References



Adams WW III, Zarter R, Ebbert V, Demmig-Adams B
(2004) Photoprotective Strategies of Overwintering
Evergreens. BioScience 54: 41 – 49
Adams WW III, Rosenstiel T, Ebbert V, Demmig-Adams B
(2001) Dependence of photosynthesis and energy
dissipation activity upon growth form and light environment
during the winter. Photosynthesis Research 67: 51 -62
Oquist G (2003) Photosynthesis Of Ovewintering Evergreen
Plants. Annual review of Plant Biology 54: 329 – 355