Stem Morphology for Quaking Aspen Populus tremuloides and Limber Pine Pinus flexilis

1. Stem Morphology for Quaking Aspen (Populus tremuloides) and Limber Pine (Pinus flexilis) By Alan Rosacker

2. My Question I wanted to look at specific winter adaptations for trees in the high montane environment The two species we will be looking at are Quaking Aspen, also known as Trembling Aspen, and Limber Pine How do different species cope with the stresses of winter? Are there many different strategies? Are there many similar strategies? These two species were chosen because they both have unique and interesting traits and because of their close proximity to the mountain research stationHow do different species cope with the stresses of winter? Are there many different strategies? Are there many similar strategies? These two species were chosen because they both have unique and interesting traits and because of their close proximity to the mountain research station

3. Overview What are the adaptations that Quaking Aspen and Limber Pine have developed to survive the winter environment? Quaking Aspen How Does Photosynthetic Bark Help Quaking Aspen? Limber Pine How Do Highly Flexible Stems Help Limber Pine? What can plants do to survive the winter And now specifically Quaking Aspen and Limber Pine Quaking Aspen has photosynthetic bark, and we want to know why. Limber Pine is extremely flexible, and we want to know what advantage this creates.What can plants do to survive the winter And now specifically Quaking Aspen and Limber Pine Quaking Aspen has photosynthetic bark, and we want to know why. Limber Pine is extremely flexible, and we want to know what advantage this creates.

4. Quaking Aspen (Populus tremuloides)The Mechanism For Corticular Photosynthesis: Photosynthetic Bark---what does that mean? The bark is made up of Photosynthetic organelles Chloroenchymes Chlorophyll-containing tissues within the stems Refixation-These chloroenchymes use the limited amount of carbon dioxide given off by the tree during respiration Some numbers: The bark of young Aspen contains up to 42% of the total tree chlorophyll- (Kharouk, 1995) 10-15% of total photosynthesis is corticular in mid summer, but larger during times where leaf contributions are limited-winter (Aschen, 2001) Light penetrates the upper layers of dead bark Chloroenchymes Chlorophyll-containing tissues within the stems Use the internal CO2 and the light that penetrates the outer layers of bark Produce starches and sugars Process follows the same rules as leaf photosynthesis Needed items: enzymes, nutrients, water, light and CO2. It is important to note that the process of photosynthesis is the same as in leaves, so all the nutrients, enzymes and water are also needed The stems do not have stomata and guard cells, and this limits the amount of photosynthesis, by limiting the amount of available carbon dioxide Some carbon dioxide is exchanged between the bark and environment, but the bulk of carbon dioxide used by the chloroenchymes to photosynthesize comes from carbon dioxide that is given off by the tree during respiration. The tissues of the tree actually gets saturated with this gas, and the chloroenchymes are able to use it for photosynthesis. Light penetrates the upper layers of dead bark Chloroenchymes Chlorophyll-containing tissues within the stems Use the internal CO2 and the light that penetrates the outer layers of bark Produce starches and sugars Process follows the same rules as leaf photosynthesis Needed items: enzymes, nutrients, water, light and CO2. It is important to note that the process of photosynthesis is the same as in leaves, so all the nutrients, enzymes and water are also needed The stems do not have stomata and guard cells, and this limits the amount of photosynthesis, by limiting the amount of available carbon dioxide Some carbon dioxide is exchanged between the bark and environment, but the bulk of carbon dioxide used by the chloroenchymes to photosynthesize comes from carbon dioxide that is given off by the tree during respiration. The tissues of the tree actually gets saturated with this gas, and the chloroenchymes are able to use it for photosynthesis.

5. The Refixation of Carbon Dioxide for Aspen Bark and Leaves under Varying Light Conditions (Aschen, 2001) These graphs show the photosynthetic efficiency of aspen leaves and twigs Performed in the SummerThese graphs show the photosynthetic efficiency of aspen leaves and twigs Performed in the Summer

6. The Refixation of Carbon Dioxide for Aspen Bark at Different Ages (Aschen, 2001) Another Important detail to bear in mind with the Quaking Aspen is the age of the tree These graphs show the different level of CO2 refixation in aspen that are 1 year different in age As the tree develops, the bark layers become thicker and less light energy can penetrate into the chloroenchymes Done in summerAnother Important detail to bear in mind with the Quaking Aspen is the age of the tree These graphs show the different level of CO2 refixation in aspen that are 1 year different in age As the tree develops, the bark layers become thicker and less light energy can penetrate into the chloroenchymes Done in summer

7. Populus TremuloidesThe Importance of Corticular Photosynthesis: So we understand the Mechanism, but why is this important? Important during stressful (winter) times-sugars can be made for the tree During non-stressful times- adds to overall photosynthesis Get a jump start when spring comes-much like many evergreen trees Recycling of internal Carbon Dioxide Creating a CO2 O2 ratio that may help in defense against phyto-pathogenic fungi (Jensen, 1969) We are talking about an energy budget, and for organisms in a winter environment anything that can give a slight edge makes a huge difference The Aspen has the potential to photosynthesize during the winter which can create extra energy for the plant Corticular photosynthesis also takes place during the summer In the spring the aspen does not have to make leaves before it can start harnessing the energy of the sun In winter the carbon dioxide that would usually be lost in respiration is refixed in photosynthesis This carbon dioxide and oxygen ratio appears to be helpful in creating an aerobic environment which helps defend against this phyto-pathogenic fungi We are talking about an energy budget, and for organisms in a winter environment anything that can give a slight edge makes a huge difference The Aspen has the potential to photosynthesize during the winter which can create extra energy for the plant Corticular photosynthesis also takes place during the summer In the spring the aspen does not have to make leaves before it can start harnessing the energy of the sun In winter the carbon dioxide that would usually be lost in respiration is refixed in photosynthesis This carbon dioxide and oxygen ratio appears to be helpful in creating an aerobic environment which helps defend against this phyto-pathogenic fungi

8. Overview What are the adaptations that Trembling Aspen and Limber Pine have to survive the winter environment Quaking Aspen How Does Photosynthetic Bark Help Trembling Aspen? Limber Pine How Do Highly Flexible Stems Help Limber Pine?

9. Limber Pine (Pinus flexilis)The Mechanism of flexibility: A study of the Goldenrod Tree (Bosea yervamora) Wide bands of Conjunctive Tissue Composed of thin-walled collenchyma cells (Carlquist, 2003) The collenchyma cells of plants usually have thickened walls which stiffen the leaves and stems (Freeman, 2002) The collenchyma cells of plants usually have thickened walls which stiffen the leaves and stems (Freeman, 2002). In the golden-rod, there are large bands of thin-walled collenchyma which allows the stem to flex more than if the normal thick-walled collenchyma were present. It seems logical that the anatomical structure that makes one plant flexible would be similar in another plant. This assumption could very well be wrong, and actual research on the relative thickness of collenchyma cells in limber pine would be required to support this claim. The collenchyma cells of plants usually have thickened walls which stiffen the leaves and stems (Freeman, 2002). In the golden-rod, there are large bands of thin-walled collenchyma which allows the stem to flex more than if the normal thick-walled collenchyma were present. It seems logical that the anatomical structure that makes one plant flexible would be similar in another plant. This assumption could very well be wrong, and actual research on the relative thickness of collenchyma cells in limber pine would be required to support this claim.

10. Collenchyma Cell Structure Collenchyma consists of elongated cells with unevenly thickened primary cell walls. It forms part of the ground tissue of�plant parts which are actively growing and lends support to the other tissues which surround it. Collenchyma is common in plant structures such as leaves, petioles, and elongating stems. The cells are well adapted for their function as their cell walls don't contain lignin and are able to stretch. They can therefore elongate as the structure they form part of, elongates. They are often found in strands or as a cylinder below the epidermis. This arrangement provides better strength than a cylinder down the middle of the stem or petiole.� Collenchyma consists of elongated cells with unevenly thickened primary cell walls. It forms part of the ground tissue of�plant parts which are actively growing and lends support to the other tissues which surround it. Collenchyma is common in plant structures such as leaves, petioles, and elongating stems. The cells are well adapted for their function as their cell walls don't contain lignin and are able to stretch. They can therefore elongate as the structure they form part of, elongates. They are often found in strands or as a cylinder below the epidermis. This arrangement provides better strength than a cylinder down the middle of the stem or petiole.�

11. Limber Pine(Pinus flexilis)The Importance of Flexibility: Branches bend under the burden of snow Thin Limber Pine branches can be bent completely back on themselves without strain or cracking �(Wier, 1998) Branches flex under high winds The stems on Limber Pine can be bent completely back on themselves. This adaptation provides the tree with many advantages during winter. Where some tree stems break under the tremendous weight of snow, Limber Pine stems are able to bend back and flex under the weight. Sometimes this bending actually allows the snow to fall completely off the tree. The stems on Limber Pine can be bent completely back on themselves. This adaptation provides the tree with many advantages during winter. Where some tree stems break under the tremendous weight of snow, Limber Pine stems are able to bend back and flex under the weight. Sometimes this bending actually allows the snow to fall completely off the tree.

12. Summary Adaptations for Winter Quaking Aspen Mechanism Chloroenchymes Refixation of carbon dioxide Function Jump start on photosynthesis Limber Pine Mechanism Wide bands of thin-walled Collenchyma cells Function Flexibility under heavy snow

13. Reference: Aschan, G; Wittman, C and Pfanz, H. (2001): Age-Dependent Bark Photosynthesis of aspen twigs.-Trees 15:431-437 Aschan, G; Wittman, C and Pfanz, H. (2002): Ecology and ecophysiology of tree stems: corticular and wood photosythesis. Naturwissenschaft 89: 147-162 Aschan, G; Wittman, C and Pfanz, H. (2001): Leaf and twig photosynthesis of young beech and aspen tress grown under different light regime. Basic Applied Ecology 2; 145- 154. http://Home.earthlink.net/~swier/LimberPine.html. Stuart Wier. Accessed 2/26/2005. Carlquist, Sherwin. (2003): Wood and stem anatomy of woody Amaranthaceae: ecology, systematics and the problems of defining rays in dicotyledons. Botanical Journal of the Linnean Society 143: 1-19. http://www.botany.uwc.ac.za/ecotree/celltissues/tissues.htm#collenchyma. Accessed 03/05/2005 Freeman, Scott. (2002): Biological Science. Prentice Hall. 604-625 Jensen, KF. (1969). Measuring oxygen and carbon dioxide in read oak trees. US Forest Service research note NE-74.