223
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_15, © Springer India 2013
15.1 Wetland Flora
(Aquatic Macrophytes) (AM)
The aquatic macrophytes (AM) are interesting
forms of plant life. As compared to the terrestrial
plants, the aquatic plants remain comparatively
less affected by the climatic and seasonal
changes. Consequently, it is more feasible to
study the plants for a greater part of the year.
Further, they also exhibit striking adaptations to
fi t in the aquatic regime.
15.1.1 Ecophysiology of Wetland
Vegetation
The chemical characteristics of warterlogged
soils are harmful to dry-land species, but the
niche is opened to a wide range of wetland plants
by adaptive modifi cations. Soil oxygen defi -
ciency demands either a transport system which
can supply it to underground organs from aerial
structures or anaerobic metabolism prevail while
toxic concentrations of Mn
2+
, Fe
2+ and S
2− persist.
H 2 S and organic compounds require either a
modifi ed metabolic chemistry which continues to
function in this hostile environment or the plant
be armed with detoxifying mechanisms. Wetland
plants must also differ from their dry-land cousins in absorbing nitrogen as NH 4
+ cation because
denitrifying microbes scavenge nitrate.
Plants inhabit soils which range from well
drained to permanently fl ooded types. Waterlogging
may not cause any problem, even though, here, the
soil pores may be totally water fi lled for many
hours after rain, causing slight anaerobiosis in the
centres of soil crumbs.
Plants with some roots in a waterlogged soil may
have to adjust with toxicity. But water and nutrient
uptake will be normal in those roots above the water
table. If the water level coincides with the soil surface, the problem of toxicity is compounded by lack
of an external oxygen supply when the water level
rises above the soil and particularly when the shoot
is fully submerged. Plants of such soils may be
stress avoiders, either by having their lateral roots
very near better oxygenated soil surfaces or by
developing superfi cial adventitious roots in response
to fl ooding. Alternatively, they may tolerate the
stress by having morphological and anatomical features which allow internal oxygen transport to fulfi l
the needs of root respiration and also for the oxidation of chemically reduced toxin. Such characteristics must also be linked to biochemical adaption
which gives tolerance during the inevitable periods
of total anoxia at the time of fl ooding. Production of
adventitious ‘water roots’ close to a fl oodwater surface is common in many waterlogging- tolerant
species. In woody plants, e.g. the willows and the
N. American blackgum ( Nyssa sylvatica ), fl ooding
fi rst causes hypertrophy of lenticel tissue to form a
callus. From this, adventitious roots then emerge
close to the better- oxygenated air–water interface.
Production of lateral roots near the surface
may be associated with other morphological
features, e.g. the ‘knees’ or pneumatophores of
some mangroves (e.g. Avicennia germinans )
15
Wetland Flora, Plankton,
Productivity, Fauna and Fishes
D. Kar, Wetlands and Lakes of the World,
DOI 10.1007/978-81-322-1023-8_15, © Springer India 2013
15.1 Wetland Flora
(Aquatic Macrophytes) (AM)
The aquatic macrophytes (AM) are interesting
forms of plant life. As compared to the terrestrial
plants, the aquatic plants remain comparatively
less affected by the climatic and seasonal
changes. Consequently, it is more feasible to
study the plants for a greater part of the year.
Further, they also exhibit striking adaptations to
fi t in the aquatic regime.
15.1.1 Ecophysiology of Wetland
Vegetation
The chemical characteristics of warterlogged
soils are harmful to dry-land species, but the
niche is opened to a wide range of wetland plants
by adaptive modifi cations. Soil oxygen defi -
ciency demands either a transport system which
can supply it to underground organs from aerial
structures or anaerobic metabolism prevail while
toxic concentrations of Mn
2+
, Fe
2+ and S
2− persist.
H 2 S and organic compounds require either a
modifi ed metabolic chemistry which continues to
function in this hostile environment or the plant
be armed with detoxifying mechanisms. Wetland
plants must also differ from their dry-land cousins in absorbing nitrogen as NH 4
+ cation because
denitrifying microbes scavenge nitrate.
Plants inhabit soils which range from well
drained to permanently fl ooded types. Waterlogging
may not cause any problem, even though, here, the
soil pores may be totally water fi lled for many
hours after rain, causing slight anaerobiosis in the
centres of soil crumbs.
Plants with some roots in a waterlogged soil may
have to adjust with toxicity. But water and nutrient
uptake will be normal in those roots above the water
table. If the water level coincides with the soil surface, the problem of toxicity is compounded by lack
of an external oxygen supply when the water level
rises above the soil and particularly when the shoot
is fully submerged. Plants of such soils may be
stress avoiders, either by having their lateral roots
very near better oxygenated soil surfaces or by
developing superfi cial adventitious roots in response
to fl ooding. Alternatively, they may tolerate the
stress by having morphological and anatomical features which allow internal oxygen transport to fulfi l
the needs of root respiration and also for the oxidation of chemically reduced toxin. Such characteristics must also be linked to biochemical adaption
which gives tolerance during the inevitable periods
of total anoxia at the time of fl ooding. Production of
adventitious ‘water roots’ close to a fl oodwater surface is common in many waterlogging- tolerant
species. In woody plants, e.g. the willows and the
N. American blackgum ( Nyssa sylvatica ), fl ooding
fi rst causes hypertrophy of lenticel tissue to form a
callus. From this, adventitious roots then emerge
close to the better- oxygenated air–water interface.
Production of lateral roots near the surface
may be associated with other morphological
features, e.g. the ‘knees’ or pneumatophores of
some mangroves (e.g. Avicennia germinans )
15
Wetland Flora, Plankton,
Productivity, Fauna and Fishes