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! Evergreen plants do not!

Types of Evergreens  Conifers Douglas fir, Limber pine, Lodgepole pine, etc.  Broad-leaf Arctostaphlos uva-ursi a.k.a. kinnikinnick

Rhododendron albiflorum Arctostaphylos uva-ursi or kinnikinnick

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, no downregulation if in the sun, but if in the shade it experiences complete downregulation 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) (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: example: top of the canopy v. forest floor top of the canopy v. forest floor

What about evergreens that are in the shade?  Experience increase in chlorophyll levels  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 photosynthesis  Both types use photoprotective mechanisms to survive mechanisms to survive

Shaded sites vs. Sun-exposed sites

Photoprotective patterns for both types of evergreens HABITAT Sun Exposed Sites Shaded Sites Above-groundgrowthNoneNone 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:  Oquist G (2003) Photosynthesis Of Ovewintering Evergreen Plants. Annual review of Plant Biology 54: 329 – 355