Wetland Plant Adaptations
Wetland environment stresses on plants
–Water regime
–Wetlands: periodic drying
–Terrestrial: periods of flooding.
–Temperature: extremes on the wetland surface due to the
shallow water.
–Anoxia leads to
–changes in nutrient supply
–toxic levels of some substances
–inefficient anaerobic respiration
–Salt
Adaptations can be broadly classified as those
that enable the organism to tolerate stress and
those that enable it to regulate stress.
•Tolerators (resisters) have functional
modifications that enable them to survive and
often to function efficiently in the presence of
stress.
•Regulators (avoiders) actively avoid stress or
modify it to minimize its effects.
•In a freshwater aquatic or soil environment, the
osmotic concentration of the cytoplasm in living cells
is higher than that of the surrounding medium. This
enables the cells to develop turgor, that is, to absorb
water until the turgor pressure of the cytoplasm is
balanced by the resistance of their cell membranes
and walls.
•In coastal wetlands, organisms must cope with high
and variable external salt concentrations.
•The dangers of salts are twofold:
•osmotic
•direct toxicity.
•The immediate effect of an increase in salt
concentration in a cell's environment is osmotic.
If the osmotic potential surrounding the cell is
higher than that of the cell cytoplasm, water
flows out of the cell and the cytoplasm
dehydrates. This is a rapid reaction that can
occur in a matter of minutes and is often lethal
to the cell.
Anoxia
Flood-tolerant species (hydrophytes) possess a
range of adaptations that enable them either
to tolerate stresses or to avoid them. There
are several adaptations by hydrophytes that
allow them to tolerate anoxia in wetland soils.
These adaptations can be grouped into two
main categories
1) Morphological
2) Physiological
1) Structural Adaptations (morphological)
a. Aerenchyma
b. Special organs or responses
Adventitious roots
Stem elongation
Hypertrophied lenticels
Pneumatophores
2) Physiological adaptations
a. Anaerobic respiration
b. Malate production
Hormones
Hormonal changes, especially the concentration of ethylene in
hypoxic tissues, initiate structural adaptations. Ethylene
stimulates cellulase activity in the cortical cells of number of
plant species, with the subsequent collapse and disintegration of
cell walls. In addition to aerenchyma development, ethylene has
been reported to stimulate the formation of adventitious roots,
which develop in both flood-tolerant trees and herbaceous
species and flood-intolerant plants just above the anaerobic
zone when these plants are flooded. These roots are able to
function normally in an aerobic environment.
Adventitious Roots
Stem Elongation
•stimulated by submergence
•in some aquatic and
semiaquatic plants
-Floating Heart (Nymphoides
peltata) right
-Wild Rice (Oryza sativa)
-Bald Cypress (Taxodium
distichum).
Aerenchyma
Allows the diffusion of oxygen from the aerial portions of the
plant into the roots.
Root aerenchyma
Root aerenchyma
Lenticels
Pneumatophores
Bald Cypress
Cypress Knees
Cypress Knees
Shallow Fibrous Root Systems
Mangroves
Dacey described an
adaptation that increases
the oxygen supply to the
floating-leaved water lily
(Nuphar luteum).
Increased air flow to the
rhizosphere is related to
increased leaf surface
temperature which
creates a humidityinduced pressurization.
Prop Roots
Red mangrove (Rhizophora
spp.) grows on arched prop
roots in topical and
subtropical tidal swamps
around the world. These
have numerous small
lenticels above the tide level
which terminate in long,
spongy, air-filled, submerged
roots.