256
modifi cations which enable it to survive and
often to function effi ciently in the presence
of stress. Conversely, ‘regulators’ (also called
‘avoiders’) actively avoid stress or modify it to
minimise its effects.
16.1 Cell-Level Adaptations
It is a fact that the range of adaptations is limited
in unicellular organisms which have little mobility. Most adaptations of this group are metabolic.
In general, these adaptations are characteristic of
cell-level adaptations because the metabolism of
all living cells is almost similar.
16.1.1 Anoxia
When an organic wetland soil is fl ooded, the oxygen available in the soil and in the water is fast
depleted through metabolism by organisms
which normally use oxygen as the terminal electron acceptor for oxidation of organic molecules.
It may be noted here that most bacteria require
organic energy sources. In contrast, nonphotosynthetic autotrophic bacteria are adapted
to use reduced inorganic compounds in wetland
muds as a source of energy for growth.
16.2 Adaptations of Vascular
Wetland Plants
In wetlands, the vascular emergent and fl oatingleaved plants are sessile. Only their roots are in
an anoxic or salty environment. Typically, the
oxygen supply rapidly decreases, if the roots of a
fl ood-sensitive upland plant are inundated. This
shuts down the aerobic metabolism of the roots,
impairs the energy status of the cells and reduces
nearly all metabolically mediated activities, e.g.
cell extension and division and nutrient absorption. Also, production of ATP is reduced when
cell metabolism shifts to anaerobic glycolysis
(Roberts 1988 ). Further, anoxia is soon followed
by pathological changes in the mitochondrial
structure. This includes swelling, reduction in the
number of cristae and the development of a
transparent matrix.
Notwithstanding the above, in contrast to
fl ood-sensitive plants, the fl ood-tolerant macrophytes (hydrophytes) possess a range of adaptations which enable them to either tolerate stresses
or to avoid stress, like root anoxia. The primary
plant strategy in response to fl ooding is the development of air spaces (aerenchyma) in roots and
stems. These allow the diffusion of oxygen from
the aerial portions of the plant into the roots.
Grosse et al. ( 1992 ) had shown in swamp trees in
Europe that seedlings and dormant (leafl ess)
trees of fl ood-tolerant species show enhanced gas
transport from the aerial shoots to the roots when
the shoots are heated by sun or incandescent
light, compared to plants in the dark. Further, the
presence of ‘oxidised rhizospheres ’ (now called
‘oxidised pore linings’ by soil scientists) is an
important way in which wetlands could be identifi ed (Tiner 1998 ). Further, intraspecifi c variations
related to metabolic and morphological characteristics point to the genetic basis for plant performance in wetland environments. Smits et al.
( 1990a , b ) had reported a positive correlation
between the number of ADH isozymes and ethanol production in the roots of a number of aquatic
macrophytes.
Concomitant to above, one adaptation which
many wetland plant species share with plants in
other stressed environments (especially, in
drought-stressed environments) is the C 4 biochemical pathway of photosynthesis. It is formally called the Hatch–Slack–Kortschak pathway
after its discoverers. It gets its identity from the
fact that the fi rst product of CO 2 incorporation is
a four-carbon compound, oxaloacetic acid.
16.3 Adaptations of Animals
Animals are exposed to almost the same range of
environmental conditions in wetlands as unicellular organisms and plants. But their adaptations
are more varied because of their complexity. The
adaptations may be as varied as a biochemical
16 Biological Adaptations to Wetland Environment
modifi cations which enable it to survive and
often to function effi ciently in the presence
of stress. Conversely, ‘regulators’ (also called
‘avoiders’) actively avoid stress or modify it to
minimise its effects.
16.1 Cell-Level Adaptations
It is a fact that the range of adaptations is limited
in unicellular organisms which have little mobility. Most adaptations of this group are metabolic.
In general, these adaptations are characteristic of
cell-level adaptations because the metabolism of
all living cells is almost similar.
16.1.1 Anoxia
When an organic wetland soil is fl ooded, the oxygen available in the soil and in the water is fast
depleted through metabolism by organisms
which normally use oxygen as the terminal electron acceptor for oxidation of organic molecules.
It may be noted here that most bacteria require
organic energy sources. In contrast, nonphotosynthetic autotrophic bacteria are adapted
to use reduced inorganic compounds in wetland
muds as a source of energy for growth.
16.2 Adaptations of Vascular
Wetland Plants
In wetlands, the vascular emergent and fl oatingleaved plants are sessile. Only their roots are in
an anoxic or salty environment. Typically, the
oxygen supply rapidly decreases, if the roots of a
fl ood-sensitive upland plant are inundated. This
shuts down the aerobic metabolism of the roots,
impairs the energy status of the cells and reduces
nearly all metabolically mediated activities, e.g.
cell extension and division and nutrient absorption. Also, production of ATP is reduced when
cell metabolism shifts to anaerobic glycolysis
(Roberts 1988 ). Further, anoxia is soon followed
by pathological changes in the mitochondrial
structure. This includes swelling, reduction in the
number of cristae and the development of a
transparent matrix.
Notwithstanding the above, in contrast to
fl ood-sensitive plants, the fl ood-tolerant macrophytes (hydrophytes) possess a range of adaptations which enable them to either tolerate stresses
or to avoid stress, like root anoxia. The primary
plant strategy in response to fl ooding is the development of air spaces (aerenchyma) in roots and
stems. These allow the diffusion of oxygen from
the aerial portions of the plant into the roots.
Grosse et al. ( 1992 ) had shown in swamp trees in
Europe that seedlings and dormant (leafl ess)
trees of fl ood-tolerant species show enhanced gas
transport from the aerial shoots to the roots when
the shoots are heated by sun or incandescent
light, compared to plants in the dark. Further, the
presence of ‘oxidised rhizospheres ’ (now called
‘oxidised pore linings’ by soil scientists) is an
important way in which wetlands could be identifi ed (Tiner 1998 ). Further, intraspecifi c variations
related to metabolic and morphological characteristics point to the genetic basis for plant performance in wetland environments. Smits et al.
( 1990a , b ) had reported a positive correlation
between the number of ADH isozymes and ethanol production in the roots of a number of aquatic
macrophytes.
Concomitant to above, one adaptation which
many wetland plant species share with plants in
other stressed environments (especially, in
drought-stressed environments) is the C 4 biochemical pathway of photosynthesis. It is formally called the Hatch–Slack–Kortschak pathway
after its discoverers. It gets its identity from the
fact that the fi rst product of CO 2 incorporation is
a four-carbon compound, oxaloacetic acid.
16.3 Adaptations of Animals
Animals are exposed to almost the same range of
environmental conditions in wetlands as unicellular organisms and plants. But their adaptations
are more varied because of their complexity. The
adaptations may be as varied as a biochemical
16 Biological Adaptations to Wetland Environment