Transcript Plant overwintering strategies

Plant
overwintering
strategies
JASON ZARNOWSKI
Over-wintering Success
 Plants, not just animals, have adapted for success in
cold climates.
 As with many evolutionary traits, there is not “best
answer”.
 Common stressors:
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Low temperatures (as low as -65°C in Siberia)
Desiccation
Mechanical Stress
Success of plants depends on overcoming
these two factors
- One strategy is
to simply die.
- Surviving
winter is an
energy
expensive
process.
- Annuals
produce hearty
seeds that
remain dormant
until conditions
become optimal
for germination.
Herbaceous Annuals
- Perennials
regenerate year
after year.
- Root stock
stays protected
below ground.
- New plant
produced from
existing roots or
bulbs.
Herbaceous Perennials
Woody-stemmed plants
 Acclimation to the cold.
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“…process by which plants each year become tolerant to
subfreezing temperatures without sustaining injury,” Marchand.
Not the process of producing “anti-freeze”.
Plants tissues can undergo “super cooling”.
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Process by which tissues are colder than freezing point without
forming ice.
Starts chain reaction of flash freezing that released latent heat.
This causes marked rise in temperature around plant stem.
Cytoplasmic water migrates from area of greater energy
(cytoplasm) to area of lesser energy (ice forming in
extracellular space).
Woody-stemmed plants
 Causes intercellular
solute concentration
to increase.
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Lowers freezing point.
 Formation of ice, not low
temperatures, causes
cell injury and death.
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Even non hardy plants
can survive -196°C in
liquid nitrogen.
Water is solidified without
being oriented into ice
crystals “vitrification”.
Shows ice
formation in
extracellular
space without
perforating
cell wall.
Woody-stemmed
Plants
Woody-stemmed plants
 Slow cooling key to even heartiest plant species.
 Rapid cooling which occurs occasionally in nature,
can cause water within cells to freeze resulting in cell
death.
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Water is trapped in the cell.
Water expands nearly 7% when it becomes ice.
Acquiring Freeze Tolerance
 Two step process that
begins in late summer,
early fall.
 First stage linked to end
of growing season.
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Translocation of
biochemical compounds.
Simple sugar
 Hormone
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 Second stage linked to
first “hard frost”.
Acquiring Freeze Tolerance
 Alteration of plant membrane also vital.
 Membrane structure and permeability altered.
 Lipid content increased for freeze tolerance.
 Decreased saturation of membrane lipids.
Crystallization point of membrane depressed.
 Lipids exhibit higher flexibility when unsaturated.
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Increased permeability of membrane offers little resistance to
water exiting the cell.
 Freeze tolerance exerts strong selective pressure for
many species.
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Tolerance often within a few degrees of average minimum
temperature in species northern limits.
Desiccation
 Dry winter winds often
cause severe desiccation to
plants exposed above
snowpack at timberline.
 Greatest water loss in most
plants is on calm, sunny
days.
 Water loss directly
proportional to water vapor
in outside air.
 Increased leaf temperature
leads to increased
evapotranspiration rate.
Desiccation
 Leaf temperatures can be
as high as 20°C above
ambient temperature due
to insolation.
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Stomates, cuticle, and
boundary layer of air offer
resistance to water vapor
loss.
Wind removes this layer of
air increasing water vapor
loss potential, but also
lowers leaf temperature
thus counteraction loss of
air layer.
Mechanical Stress
 Snow accumulated on
branches can be
substantial.
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As much as 3000 kg in
spruce uplands of Finland.
 High winds carrying ice
particles have affect of a
‘sand blaster’.
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Can abrade bark
accelerating water loss.
Thermogenic Plants
 Members of the Araceae
family.
 Bloom in late February,
early March.
 Inflorescence can be 15°35°C above ambient
temperature.
 Large starch reserves and
high metabolic rate
create heat as a byproduct.
Conclusion
 Strategy for surviving winter not a “one size fits all”
approach.
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For example, deciduous vs. evergreens.
 Different strategies work equally well for different
species.
 Adapting to cold climates is an active process.