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Halophytic Plants






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Halophytic Plants. Biology 561 Barrier Island Ecology. 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)
Halophytic Plants

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Slide 1

Halophytic Plants

Biology 561 Barrier Island Ecology

Slide 2

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

Slide 3

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).

Slide 4

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

Slide 5

Hypothetical Glycophyte/Halophyte Growth in Various Salinities

Facultative Halophyte

IntolerantHalophyte

Growth 

Obligate Halophyte

Glycophyte

Salinity 

Slide 6

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

Marine algae (Codium sp.) grow and reproduce in waters with elevated salt content

Cyanobacterium

Nostoc sp.

Slide 7

Angiosperm Halophyte Types

  • Marine angiosperms

  • Mangroves

  • Coastal strand

  • Salt marshes

Slide 8

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

Slide 11

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)

Slide 12

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

Slide 13

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

Slide 14

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

Slide 15

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

Slide 16

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

Slide 17

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

Slide 18

Responses to Increased Salts

  • Succulence Plant organs are thickened due to increased cellular water content

  • Increased growth Reduces cellular solute concentrations

Slide 19

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

Slide 20

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

Slide 21

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)

Slide 22

Summary


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