Topic 14.5 Environmental Adaptations of Plants

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Transcript Topic 14.5 Environmental Adaptations of Plants

Topic 14.5
Environmental Adaptations of Plants
Biology 1001
November 30, 2005
Introduction
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Seed & pollen dispersal means that plants occupy
numerous environments
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Plants have developed evolutionary adaptations to many
environments
These include morphological, physiological, anatomical &
reproductive modifications
Environmental stressors can be biotic or abiotic, periodic or
continuous
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Drought, flooding, cold, low light, and poor nutrient availability are
abiotic stressors
Herbivores and pathogens are biotic stressors
NewfouNdlaNd’s eNviroNmeNt
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Dwarf black spruce (Picea mariana) or “tuckamore” is an
adaptation to a cold, windy coastal environment

Influences the pattern of growth and form or morphology of the plant
Lise Sorensen
NewfouNdlaNd’s eNviroNmeNt
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Pitcher plant (Sarracenia purpurea)
 Adapted
to low nutrient availability in peatland bogs
“Sarracenia purpurea (Botanical Latin, purple, referring to the colour of the mottled pitchers) is the floral emblem of
Newfoundland and Labrador. Our pitcher plant is the stout little carnivore of Canada’s peat-quilted swamps and jellyearthed bogs, where it traps insects in leaves modified to hold water, hence pitcher plant. The slippery sides of each
pitcher are lined with downward-pointing hairs that help insects slide into the pitcher but prevent them from escaping.
Trapped without mercy, they struggle, fall exhausted back into the water, and drown in the liquid to which the plant has
added a flesh-dissolving enzyme. The decomposed bodies of the insects provide essential nutrients for the pitcher
plant.”- Bill Casselman, Common Garden Words, Macarthur and Company, 1997
PLANT Adaptations to Drought
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When water is scarce or only seasonally available, plants need to transpire
but at the same time minimize water loss
Adaptations of Plants That Endure Dry Periods
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Mechanisms to reduce transpiration rate during dry spells
- Control of stomatal opening and closing*
- Inhibition of growth of young leaves
- Leaves that roll or fold
(- Loss of leaves by deciduous trees in the autumn
- Needle-shaped leaves of conifers)
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Such mechanisms are a compromise because they also reduce photosynthesis
Roots also respond to dry periods
- Shallow root growth is inhibited
- Deep roots continue to grow to where the soil is still moist
* See Topic 14.34 Notes and Text Reading
() Loss of water due to freezing
Leaves that roll –
Ammophila arenaria
Leaves that fold - Oxalis
Xerophytes are Plants Adapted to Arid
Environments
* See Topic 14.34 Text Reading
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Mechanisms to reduce water loss while transpiring
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Waxy cuticles, sunken stomata on the lower epidermis, trichomes (hairs)
Photosynthetic stems that store water; leaves that are spines
Leaves of xerophytes may also have an abundance of fibers to provide
support when turgour pressure is low
Nerium oleander Fig. 36.16
Xerophyte Adaptations That Reduce
Transpiration
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Crassulacean acid metabolism of succulents in the family
Crassulaceae and ice plants
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Stomata stay closed during the day, open at night to take in CO2
Store CO2 as malic acid (organic acid) in vacuoles
Malic acid is broken down during the day to provide CO2
Crassula portulaceae
'Hobbit' - Baby Jade
Ice Plant
Carpobrotus edulis
ADAptations to life in water
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Excess water leads to oxygen deprivation
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The aerial roots of mangroves, called pneumatophores, provide access
to oxygen
Oxygen deprivation in other plants stimulates the production of the
hormone ethylene, which causes some of the cells in the root cortex to
undergo apoptosis, or programmed cell death
Hydrophytes are Plants Adapted to An
Aquatic Environment
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Such plants are secondarily aquatic – their ancestors evolved
on land
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Adaptations include leaf heterophyly (floating and submerged leaves
have different forms) and stomata on the upper surface of the leaf
Reproductive Adaptations to Cold
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Sun-tracking flowers
Hairy flowers that absorb IR radiation
Higher rates of asexual reproduction – stolons,
rhizomes, bulbs on flowering stalks
Salix
Allium canadense
PREDATION BY HERBIVORES
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Predation is important in chemical recycling because it returns
nutrients to the soil
Plant defenses to predation include developmental, mechanical
and chemical modifications
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Grasses are supremely adapted to grazing, continuing to grow
throughout the season due to a meristem at the base of the leaf
Spines (modified leaves), thorns (modified stems), and prickles
(epidemal outgrowths) are mechanical deterrents to predators
Chemical Defense Against Predation
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Many plants produce secondary compounds that are poisonous
or bitter tasting to animals – often the source of our drugs
Nicotine from tobacco (Nicotiana sp.)
Caffeine from coffee (Coffea arabica)
Morphine, codeine, and heroin from poppies (Papavar sp.)
Strychnine from the tropical vine Strychnos toxifera
Jackbeans produce canavanine, which replaces arginine in the proteins of
the herbivore
Coffea & Nicotiana?