Halophytic Plants

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Halophytic Plants

• Biology 561 Barrier Island Ecology

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Niceties

• 80 of the earth is covered by saline water
• Very few plants are able to tolerate saline
  conditions without serious damage
• Plants that survive in saline environments are
  termed halophytes (c.f., glycophytes)
• Most halophytes prefer saline conditions but can
  survive in freshwater environments
• Most halophytes are restricted to
• saline environments

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What is a halophyte?

• The term halophyte has not been precisely
  defined in the literature
• Plants capable of normal growth in saline
  habitats and also able to thrive on ordinary
  soil (Schimper, 1903).
• Plant which can tolerate salt concentrations over
  0.5 at any stage of life (Stocker, 1928).
• Plants which grow exclusively on salt soil
  (Dansereau, 1957).

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What is a halophyte?

• Categories of halophilism
• Intolerant Plants grow best at low salinity and
  exhibit decrease in growth with increase in
  salinity
• Facultative Optimal growth at moderate salinity
  and diminished growth at both low and high
  salinities
• Obligate Optimal growth at high or moderate
  salinity and no growth at low salinity

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Hypothetical Glycophyte/Halophyte Growth in
Various Salinities
Facultative Halophyte
Intolerant Halophyte
Growth ?
Obligate Halophyte
Glycophyte
Salinity ?
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Halophytism in Higher Plants

• Early plants developed in oceanic (i.e., high
  salinity) environments
• Marine algae
• Phytoplankton
• Cyanobacteria
• Land plants seem to have lost the
• ability to thrive under high salt
• conditions most land plants are glycophytes

Cyanobacterium Nostoc sp.
Marine algae (Codium sp.) grow and reproduce in
waters with elevated salt content
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Angiosperm Halophyte Types

• Marine angiosperms
• Mangroves
• Coastal strand
• Salt marshes

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Saline Soils

• Possess large quantities of Na
• Na adsorption on clay particles reduces Ca and
  Mg content of soils
• Marsh soils are typically
• Low in oxygen
• High in carbon dioxide
• High in methane
• Marsh soils are constantly changing due to the
  ebb and flow of the tides

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Osmotic potentials of some halophytes of the eastern coast of United States Osmotic potentials of some halophytes of the eastern coast of United States
Species Osmotic pressure (atm)
Seawater (New Jersey) 23.2
Spartina glabra 31.1
Spartina patens 31.1
Spartina michauxiana 31.1
Salicornia europaea 31.1
Distichlis spicata 28.8
Limonium carolinianum 28.8
Juncus gerardii 28.8
Baccharis halimifolia 26.1
Atriplex hastata 26.1
Hibiscus moschuetos 12.2
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Contribution of NaCl to the osmotic potential (OP) of glycophytes and halophytes Contribution of NaCl to the osmotic potential (OP) of glycophytes and halophytes Contribution of NaCl to the osmotic potential (OP) of glycophytes and halophytes Contribution of NaCl to the osmotic potential (OP) of glycophytes and halophytes Contribution of NaCl to the osmotic potential (OP) of glycophytes and halophytes
Osmotic potential of plant sap (atm) Osmotic potential of plant sap (atm) Osmotic potential of plant sap (atm)
Species OP of soil solution (atm) OP calculated as NaCl OP due to other substances Total OP
Halophytes
Atriplex portulacoides 27.7 36.4 4.7 41.1
Salicornia fruticosa 20.6 31.7 9.6 41.3
Inula crithmoides 17.0 17.6 7.1 24.7
Statice limonium 10.5 18.5 5.0 23.5
Juncus acutus 9.3 11.9 7.5 19.4
Plantago coronopus 4.0 7.7 4.0 11.7
Glycophytes
Pistacia lentiscus A 4.5 20.1 24.6
Phillyrea latifolia A 3.4 19.7 23.1
Pinus pinaster A 6.9 15.0 21.9
Quercus ilex A 2.2 24.6 26.8
A Osmotic potential was not measured but is presumably very low. A Osmotic potential was not measured but is presumably very low. A Osmotic potential was not measured but is presumably very low. A Osmotic potential was not measured but is presumably very low. A Osmotic potential was not measured but is presumably very low.
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Water Potential

• Water potential is a measure of the free energy
  (or potential energy) of water in a system
  relative to the free energy of pure water
• The water potential symbol is psi, ?
• Unit of measure (pressure) megapascals (Mpa)
  (10 Mpa 1 bar approx. 1 atmosphere)
• Pure, free water ?w 0 (the highest water
  potential value)

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Components of Water Potential

• ?w total water potential
• ?m matric potential
• ?s osmotic (solute) potential
• ?p pressure (turgor) potential
• ?g gravitational potential
• Total water potential (?w ) ?m?s?p ?g

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Typical Glycophyte
?w ?m ?s ?p ?g
Plant
?w 0 (-0.2) 0.5 0
?w -0.3
Water
?w ?m ?s ?p ?g
Soil
?w 4.0 (-0.2) 0 (-4.0)
?w -0.2
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Typical Halophyte
?w ?m ?s ?p ?g
Plant
?w 0 (-4.5) 1.0 0
?w -3.5
Water
?w ?m ?s ?p ?g
Soil
?w 4.0 (-3.0) 0 (-4.0)
?w -3.0
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Regulation of Salt Content in Shoots
Leaf surface containing salt gland of Saltcedar
(Tamarix ramiosissima)

• Secretion of salts
• Salt exported via active
• transport mechanism
• Excretion includes Na and Cl- as well as
  inorganic ions

Two celled salt gland of Spartina
Photograph and schematic diagram of salt gland of
Aeluropus litoralis
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Salt Glands in Black Mangrove (Avicennia marina)
a
(a) sunken gland on upper epidermis (b) elevated
gland on lower epipermis
b
Concentrations of secreted salts is typically so
high that under dry atmospheric conditions, the
salts crystallize
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Regulation of Salt Content in Shoots

• Salt leaching
• Not well understood, but results from transport
  of salts to the near epidermis of leaves
  precipitation leaches salts
• Salt-saturated leaf fall
• Leaves shed after accumulation of salts
• Occurs in Hydrocotyle bonariensis and others

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Responses to Increased Salts

• Succulence Plant organs are thickened due to
  increased cellular water content
• Increased growth Reduces cellular solute
  concentrations

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Seed Dispersal in Halophytes

• Most seeds of halophytes are buoyant
• Examples are glasswort (Salicornia sp.), coconut
  (Cocos nucifera), sea rocket (Cakile sp.), and
  suaeda (Suaeda maritima)
• Marine angiosperm seeds are not buoyant
• Examples are Thalassia and Halophila

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Germination in Halophytes

• Germination inhibited by high salt concentrations
• Chlorides are very toxic to germinating plants
• Optimum germination is in freshwater
• Germination response in salt water not
  necessarily correlated to later growth of a plant
  species under saline conditions
• Higher temperatures slow germination in salt water

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Physiological Response in Halophytes

• Switch from Carbon-3 photosynthesis to CAM
  (crassulacean acid metabolism)
• Stomates closed during
• the day
• CO2 fixation during
• the night
• Sugars accumulate in cells
• Decrease osmotic pressure with organic ions
  (proteins)

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Summary