PHYSIOLOGY IS:

1
TREE GROWTH AND PHYSIOLOGY (CHAPTER 4)

• PHYSIOLOGY IS
• Study of essential characteristic life
  processes, activities, and functions

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TREE GROWTH PHYSIOLOGY

• Trees can be large ( 100 m, e.g., redwood)
• Trees can be old (4000 years, e.g., bristlecone
  pine)
• These facts ? physiological problems
• 1. Transport of water, nutrients carbohydrates
• 2. Environmental insults over seasons years
• Tree growth, structure function solves the
  problems

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OUR GROWTH PHYSIOLOGY TOPICS

• Cells / tissues / organs
• Primary growth (shoots, roots, flowering)
• Secondary growth (wood production)
• Photosynthesis metabolism
• Growth regulators
• Secondary compounds
• Responses to light (shade tolerance
  intolerance, dormancy)

4
ORGANISMAL HIERARCHY

• Cells basic building blocks
• Tissues cells of like function (e.g., leaf
  parenchyma cells)
• Organs tissues working together for a purpose
  (e.g., a photosynthetic leaf)

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TISSUES

• Two Tissue Types You Should Learn
• Parenchyma
• Vascular

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PARENCHYMA TISSUES

• Continuous System of Living Cells
• Metabolism, i.e. photosynthesis, respiration
• Storage
• Conduction
• Responsible for all growth (can divide
  differentiate)

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VASCULAR TISSUE SYSTEM

• Most Abundant Tissue in Trees
• Functions
• Conduction
• Support
• Storage
• Two types
• Xylem (water mineral nutrients move up)
• In conifers through tracheids
• In hardwoods through vessels
• Phloem (carbohydrates other organic chemicals
  move down)

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ORIGIN OF CELLS, TISSUES ORGANS?

• Primary Growth (Height Length)
• Shoots roots
• Leaves
• Reproduction
• Secondary Growth (Diameter)
• Xylem (water nutrients move up through mature
  dead cells)
• Phloem (downward movement in living cells)
• Bark
• Photosynthesis (enables growth)

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PRIMARY GROWTH

• Occurs In Apical Meristem via
• 1. Cell division
• 2. Cell elongation
• 3. Differentiation into different cell (tissue)
  types
• So . . . shoot growth is at tips of branches,
  stem, and roots

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PRIMARY GROWTH (continued)

• Bud (Above Ground)
• Formed at end of growing season (usually)
• Contains complete preformed shoot including
• Apical meristem
• Leaf primordia
• Leaves
• Lateral buds
• Spring Growth From Terminal Bud
• Shoot elongates
• Leaves expand

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SHOOT GROWTH TYPES IN TEMPERATE CLIMATES

• 1. Fixed Growth
• Rapid expansion of preformed shoot and leaves
• Completed early in growing season
• 2. Free Growth
• Expansion of preformed shoot leaves (early
  leaves)
• Production of new leaves (late leaves)
• Continuous formation expansion of leaf
  primordia
• Lasts late into growing season
• 3. Recurrent Flushing (Lammas Growth)
• Like fixed growth, BUT multiple flushes per
  growing season
• Each flush ends in bud set

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LATERAL BUDS

• May produce new shoots (branches)
• May remain dormant
• Can become buried in trunk
• Stress or damage to terminal bud can release
  lateral buds to begin growth
• ? Epicormic branches (major wood quality problem
  in hardwoods)

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ROOT GROWTH

• Root growth is primary growth
• Roots have apical meristems (division,
  elongation, differentiation)
• Trees first root taproot (doesnt persist in
  all species)
• Root growth more plastic than shoot growth

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TYPES OF ROOTS

• 1. Large Perennial Roots
• 2. Fine Roots (Smaller, Ephemeral)
• Long roots length growth
• Short (feeder) roots water nutrient uptake
• 3. Mycorrhizae
• Most short roots are mycorrhizae
• Contain tissues of host tree a fungus
• Increases root surface area
• Increases resistance to pathogens
• Fungus receives carbohydrates
• Essential for tree survival

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PRIMARY GROWTH FLOWERING/REPRODUCTION

• Begins with transition
• apical meristem (indeterminate)
• floral meristem (determinate)

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FLOWERING/REPRODUCTION GYMNOSPERMS (MOST)

• Male female flowers on same tree (monoecious)
• Wind pollination
• Fertilization 1 year after pollination
• 18 months from pollination to seed maturation
• Some species retain viable seeds in cones for
  years or decades

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FLOWERING/REPRODUCTION IN ANGIOSPERMS

• Great variety in sex lives
• May be monoecious in one of two ways
• 1. Male female flowers on same tree
• 2. Perfect flowers
• May be dioecious (individual tree is female or
  male)
• Pollination via wind, insects, birds, bats, bees,
  etc.
• May disperse seeds in spring (immediate
  germination)
• May disperse seeds in fall or winter (dormant
  until spring)

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SECONDARY GROWTH

• Occurs In Lateral Meristems via
• 1. Cell division
• 2. Expansion
• 3. Maturation
• There Are Two Lateral Meristems
• 1. Vascular Cambium
• Produces xylem inside cambium
• Produces phloem outside cambium
• 2. Cork cambium produces outer bark (periderm)

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Cork Cambium
Vascular Cambium
Growth Ring
Phloem
Heartwood
Image thanks to Dr. Terry Conners
Xylem
Sapwood
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SECONDARY GROWTH (continued)

• Vascular Cambium Most Active In Spring
• Earlywood
• Xylem
• Large cells
• Thin cell walls
• Latewood
• Xylem
• Small cells
• Thick cell walls
• Annual rings due to earlywood/latewood pattern

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Cork Cambium
Vascular Cambium
Growth Ring
Phloem
Heartwood
Image thanks to Dr. Terry Conners
Xylem
Sapwood
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SECONDARY GROWTH (continued)

• Xylem Cells Lose Conductive Capacity With Age
• ? Heartwood
• All trees form heartwood
• May be colored by chemicals (may deter fungi)

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Cork Cambium
Vascular Cambium
Growth Ring
Phloem
Heartwood
Image thanks to Dr. Terry Conners
Xylem
Sapwood
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SECONDARY GROWTH (continued)

• Phloem Cells
• Capable of transport only when alive
• Short life for each cell (one or a few years)

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Cork Cambium
Vascular Cambium
Growth Ring
Phloem
Heartwood
Image thanks to Dr. Terry Conners
Xylem
Sapwood
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SECONDARY GROWTH (continued)

• Outer Bark (Periderm)
• Formed by cork cambium
• Cork cambium is outside of phloem
• Periderm forms outside of cork cambium
• Cells are dead at maturity
• Unique patterns can identify most tree species

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Cork Cambium
Vascular Cambium
Growth Ring
Phloem
Heartwood
Image thanks to Dr. Terry Conners
Xylem
Sapwood
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GROWTH REQUIRES ENERGY AND ORGANIC COMPOUNDS

• Photosynthesis
• Primarily occurs in leaves
• Ultimate source of energy for life
• The photosynthetic reaction is
• carbon dioxide water energy from light
• ?
• sugar oxygen

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AFTER PHOTOSYNTHESIS

• Metabolism Of Sugar
• 1. Releases energy
• 2. Produces organic compounds
• E.g., cellulose (structural material of cell
  wall)
• E.g., starch (storage)
• Used in spring for initial growth flush
• Usually stored in excess (allows defoliation
  recovery)

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PLANT REQUIREMENTS FOR GROWTH

• 1. Carbon dioxide
• 2. Oxygen
• 3. Water
• 4. Minerals
• 5. Light

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GROWTH REGULATORS (HORMONES)

• May promote or inhibit growth
• Can act over a distance
• Examples
• Auxin
• Cell elongation
• Apical dominance (tree form)
• In spring, bud auxin reactivates cambium
• Cytokinins (cell division, senescence)
• Ethylene (fruit ripening)
• Giberellins (stem elongation)
• Abscisic acid (dormancy in buds and seeds)

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OTHER PRODUCTS OF METABOLISM

• Lipids, Proteins, Nucleic Acids (DNA RNA)
• Secondary Compounds (Extractives)
• E.g., tannins, terpenoids, alkaloids
• Some are economically important (turpentine!)
• Natural functions often unknown
• May be defensive

33
ENVIRONMENTAL PHYSIOLOGY

• Possible Responses to Unfavorable Environment
• More efficient use of a limiting factor (e.g.,
  rapid shoot elongation if light is limiting)
• Stress reduction (e.g., stomatal closure during
  water stress)

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ENVIRONMENTAL PHYSIOLOGY (continued)

• Responses To Daily Light Duration (Photoperiod)
• Short days
• Bud set
• Leaf senescence
• Abscission
• Long days
• Free growth (recurrent flushing)
• Flowering
• These responses are relatively rapid

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ENVIRONMENTAL PHYSIOLOGY (continued)

• Responses To Light Quantity
• Shade-intolerant species require full sun
• Shade-tolerant species can grow in shade (low
  respiration rates)
• These responses are evolutionary

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ENVIRONMENTAL PHYSIOLOGY (continued)

• Nitrogen is often limiting to tree growth
• Abundant in air but not directly usable
• Abundant in soils but often in unusable forms
• Some trees can convert atmospheric nitrogen into
  usable forms (nitrogen fixation)
• Conversion is by symbiotic microorganisms
  (bacteria, fungi) on roots
• Tree provides carbohydrates to the symbiont
• Nitrogen-fixing trees often early-successional

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ENVIRONMENTAL PHYSIOLOGY (continued)

• Future Challenges To Trees
• Global climate change
• Changes in atmospheric chemistry