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10/28/2013 2
Tree Biology
• Gain an understanding of basic tree biology
• Focus on the 3 main components of a tree
• Learn how biology relates to function
• Understanding trees will make you better arborists in the future
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What is a Tree?
“A tree may be defined as a woody plant reaching 20 feet or more at maturity, with a single trunk and a definite crown”
Harlow, Harrar, Hardin and White;
Textbook of Dendrology
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The Leaves
The Stem
The Roots
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Six Organs of Plants
• Leaves
• Stems
• Roots
• Cones
• Flowers
• Fruit
Put these all together and you have a fully
functioning (organism) or a tree.
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All Trees Fall into Two Categories
Angiosperms (flowering plants)
Contain petals, sepals, pistil, and stamen. *Not always on the same flower or plant.
Gymnosperms
(flowerless plants)
Contain pollen-producing cones and seed-producing cones. *Not always on the same plant.
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Decurrent
Excurrent
Tree Forms
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5% Leaves 15% Limbs 60% Trunk 15% Woody Roots 5% Absorbing Roots
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Animal and Plant Cells
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Animals and Plants
Similarities Animal Cell Plant Cell
Cytoplasm: Present Present
Endoplasmic
Reticulum
Present Present
Ribosomes: Present Present
Mitochondria: Present Present
Golgi
Apparatus:
Present Present
Microtubules/
Microfilaments:
Present Present
Flagella: May be found in
some cells
May be found
in some cells
Nucleus: Present Present
Differences Animal Cell Plant Cell
Cell wall: Absent Present (formed of
cellulose)
Shape: Round (irregular
shape)
Rectangular (fixed
shape)
Vacuole: One or more small
vacuoles (much
smaller than plant
cells).
One, large central
vacuole taking up 90% of
cell volume.
Centrioles: Present in all animal
cells
Only present in lower
plant forms.
Chloroplast: Animal cells don't
have chloroplasts
Plant cells have
chloroplasts because
they make their own
food
Plastids: Absent Present
Plasma
Membrane:
only cell membrane cell wall and a cell
membrane
Lysosomes: Lysosomes occur in
cytoplasm.
Lysosomes usually not
evident.
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Autotrophs vs. Heterotrophs
• Trees are photoautotrophs that fix their own energy from sunlight using photosynthesis. Autotrophs are the producers in ecosystems.
• Heterotrophs (like humans) depend upon energy from other organisms. There are consumers (herbivores, carnivores, omnivores), detritivores (worms), and decomposers (fungi).
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Energy and Gas Exchange
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The Leaf Top Side
Bottom Side
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Leaf Structure
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Leaf Anatomy
Sun Leaf vs. Shade Leaf
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Leaf Anatomy
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Photosynthesis
• Overall, water, carbon dioxide, and sunlight produce glucose and oxygen.
• 6 CO2 + 6 H2O + energy = C6H1206 + 6 CO2
• Sunlight and water create short-term plant energy (ATP and NADH).
• This ATP and NADH energy creates “glucose” from CO2 and RuBP.
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Types of Photosynthesis
• C3, C4, CAM. All three use the Calvin cycle as the final stage of photosynthesis. Plants with the added steps of C4 and CAM grow slower, but conserve water better than C3 alone
• C3 plants include most trees and shrubs.
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Respiration
• Sugar and oxygen produce carbon dioxide, water, and plant energy.
• C6H1206 + 6 CO2= 6 CO2 + 6 H2O + energy
• Oxygen’s main job is to bind with extra Hydrogen and let the system cycle.
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Carbon cycling
• 6 CO2 + 6 H2O + light = C6H1206 + 6 O2
• C6H1206 + 6 O2 = 6 CO2 + 6 H2O + ATP
• During good growing days, photosynthesis out performs respiration by 40 to 70%. This allows extra sugars to be converted into the growth of wood (fixed carbon). Thus, more O2 than CO2 is released into the atmosphere.
• However, respiration occurs year round on all perennial plants. Any time a plant is not actively growing, it releases as much or more CO2 as O2.
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Gas Exchange
• Stomata
• Lenticels
• Collenchyma cells
• Root Absorption
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Photosynthesis Video
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Types of Leaves
Deciduous: leaves are shed usually annually (in the fall).
Evergreen: leaves are persistent, stay on longer than one year.
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Leaf Fall
Abscission zone– area at the base of the petiole that breaks down and causes leaf (or fruit) drop
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Leaf Fall Declining intensity of sunlight triggers the processes leading up to leaf fall in autumn.
Clogged phloem veins trap sugars in the leaf and promote production of anthocyanins
Chlorophyll reduces, unmasking carotenoids.
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Stems: The Arms of the Tree
Petiole – leaf stalk
Abscission zone, base of the leaf stalk
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Leaf scar: zone of abscission.
Bundle scars (dots) within the leaf scar.
Leaf Scar
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Stem terms
• Function: to provide support for leaves, buds and fruit.
• Bud : protuberance on the stem that may develop into a flower or shoot. – Apical: terminal or end bud (dominant)
– Lateral: aka auxiliary, occur along the stem.
– Adventitious: undifferentiated cells under the bark which develop into a bud. (Usually due to loss of normal bud) (root sucker)
– Dormant: suppressed buds laying in wait beneath the bark
• Epicormic shoot: Shoot produced by dormant or adventitious buds. (Usually in response to stress).
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Pruning or Topping?
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Stem terms
• Node: Enlarged portion of the stem where buds and leaves arise.
• Internode: Area between the nodes.
• Bud scale scars: point below a bud where bud scales were attached. (Good for identifying growth rate)
• Lenticels: small opening along the stem that permit gas exchange. ( little specs)
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Learn what is normal and what is not.
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Twigs (small stems)
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A strong branch union is formed by overlapping layers of branch tissue and stem tissue.
Branch ( larger stem):
Branch bark ridge
Function to support twigs and transport.
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From Leaves and Stems to Roots
Now that we have explored how leaves work, we are going to examine the foundation and root system.
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Root Structure
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Absorbing roots (many)
Sinker roots (few) Tap root (rare)
Lateral roots (many)
Mycorrhizae: beneficial fungi. Symbiotic relation with absorbing roots. Facilitate the absorption of water and nutrients.
Root Structure
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Root Structure
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Root System
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Concrete sidewalk
Compacted soil, few macro pores
Moist loose friable soil.
Roots are opportunistic,they grow where conditions are best.
O2 O2
O2
O2
Root crown
Root Growth
Dry soil, little oxygen
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Zone of rapid taper
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Root Development
• The most important part of the root does not have a woody covering yet.
• Single-cell root hairs provide most of the tree’s water and nutrient uptake from the soil.
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Root Development
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Root Function
1. Support and Anchor the Tree 2. Absorption and Conduction of
Water and Nutrients 3. Storage of Food and Nutrients
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It all starts with SOIL
• As we know, 99% of a tree’s root mass is in the top 3 feet of soil.
• This is where the tree absorbs water stored in soil from rainfall and the intake of vital nutrients (N-P-K).
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Soil Types and Horizons
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Soil Nutrients
• Nitrogen, phosphorous, potassium, calcium, Magnesium, Sulfur, Iron, Manganese, Zinc, Copper, Boron, Molybdenum, and Chlorine are all considered essential to plant growth.
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Water and Nutrient Uptake
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Roots Video
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Xylem and Phloem: Tree Transportation Highways
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The Main Stem (Bole or Trunk)
• The trunk and branches of a tree provide the tree’s framework.
• They conduct water and minerals from the roots to the leaves.
• They also store energy in the form of sugars and starches.
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What makes a plant a tree?
Like other plants: • Trees are autotrophs - meaning they produce
their own food. • Tree cells have rigid cell walls, a large central
vacuole, and chloroplasts.
The difference is Secondary Growth!
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Secondary Growth means Wood!
Trees and shrubs grow
radially as well as vertically.
(The difference between trees and shrubs is size.)
Expanded concept of a tree
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Grow Upward and Outward
Trees Grow in Layers.
1
2
3
4
5
6
On ring porous trees
they are easiest to
count. Either count all
the light colored rings
or all the dark colored
rings to determine the
age.
Seasonal production
of xylem by the
cambium.
Grow Rings.
Ring Porous (oak, ash, elm)
Diffuse Porous (maple, sycamore, poplar)
http://botit.botany.wisc.edu/images
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Growth & Development
• A tree can only get as large as it is genetically capable.
• Limiting factor(s): Environmental surrounding conditions.
• Respond to environmental stimulus. (light, temperature, water, gravity)
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Tropisms
Tropisms are Orientation or Direction of growth in response to…
• Geotropism – Gravity
– Stems grow up against gravity
– Roots grow down with gravity
• Phototropism – Light
– Growing in the direction of light
• Thigmotropism – Touch or Contact
– Roots growing around a rock in the soil
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Main Stem Anatomy • Vascular Cambium: Area of cell division that is responsible
for secondary growth. Creates and separates the xylem and phloem.
• Xylem: Grows to the inside of the vascular cambium to transport water and nutrients from roots to leaves. Prominent cells are vessels, tracheids, fibers (Angiosperm) or tracheids (Gymnosperm).
• Phloem: Thin layer growing on the outside of vascular cambium to transport nutrients down from leaves. Prominent cells include sieve tubes and companion cells.
• Cork Cambium: Area of cell division that forms bark and lenticels to the outside. Designed to protect inner cells and allow gas exchange.
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Xylem (wood)
• Water conducting ( trees are different)
– Conifers : 2 – 12 years of active sapwood
– Elm : 1 -2 years of active sapwood
• Important: When treating trees with systemic pesticides.
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Phloem
• Composed primarily of living cells(symplasm) – Sieve Cells: in Gymnosperms (conifers)
– Sieve tube elements & companion cells: in Angiosperms (hardwoods)
– Old phloem, gets crushed and absorbed back into system or into bark layers
• Carbohydrates move slowly
• Usually stay near area of production and used locally
• Requires energy to transport along pressure gradients, actively pumped to different parts.
• Source to Sink ( leaf to plant part)
• Sink uses more energy than it produces.
• Photosynthates can move either up or down.
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Xylem and Phloem
XylemPhloem
Cambium
Vascular cambium
Xylem Phloem
Movement of water, elements and food is in all directions. Xylem and Phloem move resources up and down along the tangential plane. Longitudinal or
Axial transport
Movement horizontal between cells of all ages is called.
Radial transport
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Cross Section of Woody Stem
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Water Transportation Video
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Compartmentalization
Vascular plants differ from us greatly when faced with wounding or infectious diseases. Unlike us, they lack IMMUNE systems. Instead, they have developed a process to cope known as: Compartmentalization
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CODIT Compartmentalization of Decay In Trees
The 4 Walls 1. Tyloses
2. Axial parenchyma and annual
growth components
3. Ray cells
4. Wound response of cambium
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CODIT: Trees don’t Heal, they SEAL
• A wounded tree will NOT be capable of healing a wound by regenerating destroyed tissue.
• Instead, the wound is “walled” off from the rest of the vascular system by the formation of “TYLOSES” thus, not allowing decay to spread into the rest of the system.
• There are four walls or boundaries
• It’s like a submarine or spaceship sealing off decks to save the rest of the ship (tree).
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CODIT
• Wall 1: Stops VERTICAL Spread by plugging vessel & tracheid cells in the xylem (weakest boundary).
• Wall 2: Stops INWARD spread toward the pith.
• Wall 3: Stops LATERAL movement by plugging cells that are primarily for food storage (strong boundary).
• Wall 4: Separates NEW wood from that which was present from the time of the damage (the strongest boundary).
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Natural Branch Abscission
• Compartmentalization also occurs at branch collar and leaf collars.
• This CODIT prevents injury to the tree when it is time for a branch to go.
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• Let’s examine the CODIT process in several stage over time
CODIT in Action
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What does it all mean?
• Trees can live longer than other plants.
• They can get bigger than other plants.
• They can respond to damage, disease, insects, and environmental conditions successfully.
• Trees are a long term investment.
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Tree System Review The Leaves process water and carbon dioxide (Photosynthesis) to form complex sugars (fuel), which are sent back down (Phloem) the tree for storage and use.
The Stem transports water and solutes (Diffusion & Osmosis), to the crown via the Xylem.
The Roots absorb water and nutrients with help from Root Hairs.
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The End
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For More Information
Texas Forest Service
Brad Hamel
(512) 339-4618
Texas Forest Service Website:
http://texasforestservice.tamu.edu
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Definition of Cellular Terms • Cytoplasm: the protoplasm of a cell contained within the cell membrane but excluding the nucleus: contains organelles,
vesicles, and other inclusions.
• Endoplasmic Reticulum: an extensive intracellular membrane system whose functions include synthesis and transport of lipids and, in regions where ribosomes are attached, of proteins.
• Ribosomes: any of numerous minute particles in the cytoplasm of cells, either free or attached to the endoplasmic reticulum, that contain RNA and protein and are the site of protein synthesis.
• Mitochondria: Also called chondriosome, a small spherical or rod like body, bounded by a double membrane, in the cytoplasm of most cells: contains enzymes responsible for energy production.
• Golgi Apparatus: a membranous complex of vesicles, vacuoles, and flattened sacs in the cytoplasm of most cells: involved in intracellular secretion and transport.
• Microtubules/ Microfilaments: a hollow cylindrical structure in the cytoplasm of most cells, involved in intracellular shape and transport.
• Flagella: a long, lashlike appendage serving as an organ of locomotion in protozoa, sperm cells, etc.
• Nucleus: a specialized, usually spherical mass of protoplasm encased in a double membrane, and found in most living eukaryotic cells, directing their growth, metabolism, and reproduction, and functioning in the transmission of genic characters.
• Cell wall: the outer layer of a cell, especially the structure in plant cells that consists of cellulose, lignin, etc., and gives mechanical support to the cell.
• Vacuole: a fluid-filled cavity in the cytoplasm of a cell.
• Centrioles: either of two rodlike bodies in most animal cells that form the poles of the spindle during mitosis.
• Chloroplast: a plastid containing chlorophyll and other pigments, occurring in plants and algae that carry out photosynthesis.
• Plastids: a small, double-membraned organelle of plant cells and certain protists, occurring in several varieties, as the chloroplast, and containing ribosomes, prokaryotic DNA, and, often, pigment.
• Plasma Membrane: a very thin membrane composed of lipids and protein that surrounds the cytoplasm of a cell and controls the passage of substances into and out of the cell.
• Lysosomes: a cell organelle containing enzymes that digest particles and that disintegrate the cell after its death.
