Biological Adaptations to the Wetland Environment

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Biological Adaptations to the Wetland Environment
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Stress

• external pressures put on an organism by an
  environmental factor
• aquatic species not adapted to periodic drying
  stress
• terrestrial species not adapted to periodic
  flooding
• wetland species have to be adapted to both

Biotic feedback
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Strain

• degree to which the physiology of the organism is
  damaged by that stress

Biotic feedback
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Ways of dealing with an environmental
stress/constraint

• stress avoidance - prevent penetration of stress
  into tissues barrier used to prevent stress from
  causing strain
• stress tolerance - allow stress to enter tissues
  but avoid expected internal damage (prevent,
  decrease, or repair strain)

Biotic feedback
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Flooding Stress

• hypoxic or anoxic soil conditions
• supply of nutrients cut off
• buildup of toxic materials
• roots of actively growing plants need O2 to
  respire
• roots cannot extend and divide
• strong selective pressure to address problems of
  hypoxia

Biotic feedback
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Stress Avoidance (Regulators)

• evolution of air spaces (lacunae) from leaf
  parenchyma extends to petiole, stem, and buried
  rhizome or root
• hormonal changes (buildup of ethylene) initiate
  structural changes
• splits between cells or disintegration of cells
• system of lacunae is aerenchyma tissue
• passive diffusion of O2
• as roots elongate can oxidize their surroundings
  (oxidized rhizophere), which may benefit
  neighboring plants too

Biotic feedback
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Aerenchyma Tissue

• very well-developed in emergent marsh and aquatic
  plants

Biotic feedback
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Stress Avoidance (Regulators)

• pressurized bulk flow of O2 if an internal
  pressure gradient exists
• See handout of water lily
• into young leaves, petiole, rhizome, up older
  petiole and out older leaves
• 22 L of air can enter a leaf and flow to
  rhizome!

Biotic feedback
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Stress Avoidance (Regulators)

• woody species typically do not have these
  morphological adaptations
• exceptions that have aboveground extensions of
  roots (pneumatophores) give roots access to
  atmospheric gases
• Avicennia (mangrove)
• Taxodium (bald cypress)
• Nyssa (water tupelo)

Biotic feedback
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Stress Avoidance (Regulators)

• lenticels smalls pores where CO2 and O2
  exchange occurs

Biotic feedback
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Stress Avoidance (Regulators)

• adventitious roots develop above anaerobic layer

Biotic feedback
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Anaerobic Decomposition

• toxic compounds are formed from anaerobic
  decomposition of organic material
• ammonia, ethylene, hydrogen sulfide, acetone, and
  acetic acid build up
• flood-intolerant species response
• stomata close, transpiration and PSN decrease, N
  P tissue concentrations drop, growth declines
  and the apical meristem degenerates

Biotic feedback
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Stress Tolerance (Resisters)

• flood-tolerant species response
• modified metabolic pathway avoid production of
  ethanol
• some produce malate
• others increase catalysis of acetaldehyde to
  ethanol but doesnt accumulate leaks out or
  diffuses out from roots

Biotic feedback
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Stress Tolerance (Resisters)

• rhizomes can survive extended periods of time
  under anaerobic conditions

Biotic feedback
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Stress Tolerant Animals

• Amazonian fish in drying floodplain
• 9-10 families can remove O2 from atmosphere
• swim bladders can act like a lung
• catfish can use stomach to remove O2 from
  swallowed air
• expansion of lower lip to increase ability to
  extract O2 from water (like a gill)
• fish move water over gills
• diurnal migration of fish
• resting structures (clams, sponges, cladocerans)
• of the reptiles, turtles most tolerant of hypoxia
  (pump water in/out throat and submerge)

Biotic feedback
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Grimes CSR Theory
stress tolerator
ruderals
competitors
Biotic feedback
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Secondary Constraints - Flooding

• Peatlands organic material accumulates
• decomposition is slow because water table is at
  surface
• little/no contact with mineral soil
• plants dependent on dilute nutrient concentration
  from rainwater

Biotic feedback
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Secondary Constraints - Flooding

• low fertility more leathery evergreen species
  (sclerophylly) because deciduous foliate too
  expensive
• extremely infertile soils, dominance by
  carnivorous plants (e.g., pitcher plant bog)

Biotic feedback
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Pitcher plant bog
Sundews
Biotic feedback
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Secondary Constraints - Flooding

• Aquatic permanently or semi-permanently flooded
• constant submergence
• wave action
• lower diffusion of CO2 in water could affect PSN

Biotic feedback
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Plant Adaptations to Aquatic Habitat

• highly developed aerenchyma
• modified flowers
• dissected submersed leaves (increased surface
  area to volume)
• floating leaves
• reduced waxy epidermis
• reduced leaf thickness

Biotic feedback
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More Plant Adaptations to Aquatic Habitat

• uptake of bicarbonate ions rather than CO2
• uptake of CO2 through roots instead of leaves

Biotic feedback