Halophytes Flashcards
what are the structural adaptations of Halophytes ?
- Aerial root systems called pneumatophores
- Filtration structures in roots
- Salt glands
what are the physiological adaptations of halophytes?
- Concentrates and stores salts in vacuoles
- Accumulates salts in leaves or bark.
how does an aerial root system called pneumatophores work and give an example
aid in respiration. the muddy oxygen-poor soils that characterise these areas do not hold enough oxygen for these trees to effectively respire. oxygen diffuses into the spongy tissue of the pneumatophores. they grow upwards out of the water or mud or reach the air. e.g. mangroves
how does filtration structures in roots work and give an example.
Prevent salt from entering their roots. Mangroves have an ultrafiltration system that can filter approximately 90% of sodium ions from the surrounding salt water. the three layers of the filtration system surrounding the roots trap sodium ions but allow water to pass through as it is pulled into the xylem. e.g. mangroves
how do salt glands work and give an example
salt is directed to plant surfaces, where salt glands secrete salt to reduce salt content in the plant. e.g. mangroves
how does concentrates and stores salts in vacuoles work and give an example
stores salt in the vacuoles of the fleshy stem segments or ‘beads’, which can have salt concentrations of 30-45%. the salt in the beats becomes highly concentrated, and they shrivel, die then drop off. this allows the rest of the plant to remain healthy. e.g. samphire, an Australian succulent.
how does accumulates salts in leaves or bark work and give an example
salt is directed to older leaves or bark, where is accumulates. The leaves or bark eventually die and drop off, removing the salt from the plant. e.g. Samphire, and Australian succulent.
how does a thick, waxy cuticle aid in water retention
structural
Provides a waterproof covering preventing evaporation of water
Transpiration through stomata only – regulated
E.g. Mulga, Eucalypts
how do Upward Sloping Leaves & Branches aid in water retention
structural
= Tusic Shape
Water/rain runs down leaves, branches and stems, concentrated around roots at base of plant.
Also, to a lesser degree, reduces direct sunlight = less heat = less transpiration
Eg. Mulga
how does a Stomatal Closure aid in water retention?
structural
Guard cells shrink, closing stoma, during times of low water (you already know about this one)
Reduces transpiration
how do curling leaves aid in water retention?
structral
Leaves curl over trapping moist air = less transpiration
Fewer stomata directly exposed to external environment.
E.g. Porcupine grass
Spinifex
how do Ephemerals aid in water retention
structural
Plants with a very short life-span.
Seeds only germinate after sufficient rain.
Then grow, flower and seed while conditions are favourable.
Eg. Gunniopsis intermedia
how do Deciduous plants reserve water
structural
Lose their leaves when water is not available.
Eg. Autumn fagus
how has a Shiny cuticle / Hairy Leaves aid in water retention?
structural
Increase reflected light = less heat = less transpiration.
Eg. Magnolia
how do Vertically Hanging Leaves aid in water retention?
Structural (some say Behavioural)
Less SA to sunlight = less heat = less transpiration
Water/rain runs down leaves, dripping around roots at base of plant.
Eg. Eucalypts
how do needle shaped leaves aid in water retention
structural
Less SA to sun
Eg. Pines
how do extensive roots aid in water retention
structural
Spread thoroughly just under the surface to absorb maximum water (even dew)
Eg. Spinifex
+Grass tree
how does a sunken stomata aid in water retention?
structural
Stomata recessed (or enclosed in cavity) allows small pocket of trapped water vapour
Eg. Some cacti
how does stomata on the underside of the leaf aid in water retention ?
Structural
Less exposure to direct sunlight
Eg. Most plants
how does a reduced leaf size aid in water retention
Structural
Decrease SA = reduced transpiration
Eg = Geraldton Wax
important things to know about halophytes
Plants that survive in saline environments are termed halophytes
Most halophytes prefer saline conditions but can survive in freshwater environments
Most halophytes are restricted to saline environments
morphological adaptations on the leaves of halophytes
Leaves are thick and their surfaces are reduced.
morphological adaptations on the stem of halophytes
Well developed aerial stem and much branched.
The stem ranges from soft to hard woody type.
morphological adaptations on the roots of halophytes
Tap root system is not much elaborate and deeply penetrating. In many cases, roots are negatively geotropic.
rate of transpiration in halophytes adaptation
Like xerophytes, the rate of transpiration is checked by various kinds of morphological and anatomical modification of leaves
gas exchange of halophytes
Gases exchange of the aerial plant parts takes place normally but the respiration of underground parts i.e. roots take place by the formation of negatively geotropic roots known as pneumatophores.
absorption of water for halophytes
Absorption of water and mineral salts takes place slowly and selectively by the elaborate root system.
what are the physiological features to discuss with xerophytes and halophytes?
- rate of transpiration
- gas exchange
- absorption of water
Explain two distinctly different adaptations of halophytes to high-salt environments.
A definition of halophyte and their typical environment:
Halophytes are plants that are able to survive in environments of high salt concentration, e.g. mangrove trees.
A explanation of TWO of the following adaptations:
Store salt in vacuoles in root cells: salt concentration in the cell exceeds that in soil, thus water moves into the root.
Accumulate salt in leaves/bladders/salt glands/bark: discard salt/leaves/bladders which reduces the amount of salt in plant.
Store salt in cell vacuoles: removes salt from cell cytoplasm which stops salt from interfering with cell function.
Accumulate/store water in leaves/some parts of plant: dilutes salt content of cells in these parts of plant and provides a water store for drier periods.
Prevent salt entering/regulate amount of salt: filtration mechanism at roots which avoids the plant having to deal with excess salt.
