Biological Adaptations to the Wetland Environment
Two problems that biota face in wetlands
1. Anoxia - depletion of oxygen in soil and water
in a flooded wetland
2. Salt - changes osmotic potential and when
concentrations in the cell are high, it can be toxic
(inactivate metabolic enzymes)
Bacteria
Cyanobacteria
Single-celled protists
Adaptations to anoxia
-anaerobic respiration
ex. Thiobacillus and Desulfovibrio are
bacteria that are part of sulfur cycle. Thiobacillus
oxidixes elemental sulfur (or hydrogen sulfide) to
form sulfates. Desulfovibrio uses sulfates as the
terminal electron acceptor and hydrogen sulfide is
produced
Adaptations to salt
-active transport using sodium potassium pumps
to accumulate potassium and dilute sodium
Plants-Mosses
Sphagnum or peat moss
Liverwort
Ferns
Horsetails
Gymnosperm
Angiosperm
Adaptations to anoxia
-anaerobic respiration
Plants that are adapted to wetlands contain
enzymes other than ADH and are not poisoned
by alcohol accumulation. MDH that produces
malate is a common example of an enzyme
utilized for anaerobic respiration in wetland
plants.
Aerenchyma and adventitious root development
above anaerobic zone are stimulated by hormone
auxin that triggers growth of adventitious roots. New
growth releases ethylene that accumulates in roots
under anaerobic conditions such as waterlogged soils.
Ethylene stimulates the formation ofcellulase that
opens up cortex as aerenchyma.
Examples of common plants with adventitous roots
and aerenchyma are water lilies, mangroves, and bald
cypress. Water lilies have floating leaves.
Mangroves and bald cypresses have pneumatophores
that contain aerenchyma and function as respiratory
organs. Buttress roots often contain aerenchyma and
provide support for woody plants.
hypertrophied lenticels - enlarged lenticels
that are more numerous on stem increase
oxygen uptake during inundation
rhizosphere oxidation - oxygen diffusing from the
roots reacts with potentially toxic reduced ions
forming oxidized forms that precipitate out of the
rhizosphere (ie iron(II) to iron (III) and manganese
(II) to manganese (III)).
Adaptations to salt
1) periderm, a thickened epidermis, is a barrier
protecting inner tissues.
2) salt secreting glands - secretory organs on
leaves.
3) C-4 photosynthesis reduces water loss via
transpiration when stomates are closed during
dry or saline conditions.
C-3 photosynthesis works well
as long as stomates remain open.
C-4 photosynthesis keeps carbon dioxide
concentration high so photorespiration
does not occur.
Photorespiration when stomates
Close produces a 2-C compound
that cannot be used to make sugar.
Adaptations involving nutrient absorption
1) water - plants intolerant to anaerobic
environments have poor root metabolism and
respond as if in drought situation- stomates
close, decreased transpiration, and wilting.
Countered by adventitous roots,
aerenchyma, and enlarged lenticels
2) nitrogen - In wetlands, nitrates are reduced to
ammonium that is toxic. Wetland plants maintain
normal rates of nitrogen uptake by converting
ammonium to nitrate in rhizosphere or have the
ability to absorb ammonium directly and convert it to
amides. Others have increased levels of nitrate
reductase so that when nitrates are absorbed they can
more efficiently convert them to amide groups to be
used in synthesizing amino acids.
Some wetland plants are carnivorous and
obtain nitrogen from exoskeletons.
3) phosphorous - availability increases in waterlogged soils.
4) iron and manganese - increase can be toxic by
inactivating enzymes. Rhizosphere reduces that
toxicity by oxidation and subsequent precipitation.
5) sulfur - sulfides produced by anaerobic bacteria
are toxic. They affect enzymes such as those needed
for respiration. May be overcome by oxidation in
rhizosphere and accumulation of sulfates in vacuoles.
Adaptations involving reproduction
1) timing of seed production innonflood season
by delayed flowering
2) hydrochory. Fruits or seeds adapted to
floating and fungal resistant.
3) vivipary. Seeds germinate on the plants and
seedlings drop into the water. Example:
mangroves
4) prolonged seed viability Ex bald cypress seeds
remain viable for 20 years or more and germinate
during infrequent periods when soil isdewatered.
5) flood tolerant seeds and seedlings. Some
species can germinate underwater or have
seedlings that survive inundation. For example
ashes have seedlings that can survive inundation.
Animals have six major adaptations to anoxia.
1) Modifications for gaseous exchange.
Examples include gills andparapodia.
2) Mechanisms to improve the oxygen gradient
across a membrane. For example, cilia moving
water over gills or animals swimming to oxygenrich water.
3) Better circulatory system.
4) Use of more efficient respiratory pigments in
blood and/or higher concentrations of these
pigments. For example, mollusks have
hemocyanin (copper based) while the annelids
have more efficient hemoglobin.
5) Low oxygen behaviors such as reduced motility or
closing a shell.
6) Increased metabolism or heart pumping rates.
Three Major Adaptations to Salt in Animals
1) nephridia help retain water and eliminate
salts in concentrated urines.
2) salt secreting glands.
3) Reproduction with large numbers of larvae that
are distributed widely and can tolerate a variety of
salinity changes so that some survive.
Plants are wetland indicators because of their
adaptations and demarcate wetland boundaries.
Some common angiosperm plant families
and a few examples of species found in
North-central Texas Wetlands
Aceraceae (maple)
Trees or shrubs with reduced flowers that produce
winged fruits called samaras.
Morphological adaptations: adventitious roots,
hypertrophied lenticels.
Acer negundo
Alismataceae (arrowhead)
Herbs with linear to lanceolate or arrowhead-shaped
leaves with three sepals and petals as well as many
stamens and pistils. Most are in wetland habitats.
Morphological adaptations: polymorphic leaves
(linear when submerged, broader when emergent).
Asteraceae (sunflower)
Small flowers in heads.
Physiological adaptation: Senecio vulgaris has a
slight increase in metabolism under anaerobic
conditions as compared to non-wetland species that
have large increases.
Cupressaceae (cypress or cedar)
Trees or shrubs with scale-like leaves and small
woody cones.
Morphological adaptations: buttressed trunks and
pneumatophores.
Cyperaceae (sedge)
Grasslike herbs often having edged
stems and a single bract covering
each of its many reduced flowers.
Most are in wetland habitats.
Morphological adaptations: inflated
stems and leaves
Physiological adaptations: Some
have been shown to have malate
accumulation and lack of ADH activity.
Cyperus strigosus
Carex
Juncaceae (rush)
Grasslike herbs with round stems and basal, tufted
leaves as well as six papery flower parts. Most are in
wetland habitats.
Morphological adaptations: inflated stems and leaves
Physiological adaptation: Juncus effusus can grow
roots under very low oxygen conditions and does not
have ADH activity.
Lythraceae (loosestrife)
Herbs with 4-6 crumpled petals on the edge of a
floral cup (crape-myrtle is a cultivated shrub in this
family).
Physiological adaptation: Lythrum salicaria has no
ADH activity.
Nymphaceae (water lily)
Herbs with floating round or heart-shaped leaves and
large, showy, many-parted flowers. All are in
wetland habitats.
Morphological adaptation: floating leaves.
Oleaceae (olive)
Trees or shrubs with opposite leaves and four parted
flowers having two to four stamens.
Morphological adaptations: buttressed trunks and
adventitious roots.
Physiological adaptation of Fraxinus (ash): oxidizes
the rhizosphere.
Poaceae (grass)
Herbs with round stems and
reduced flowers enclosed in
two bracts.
Physiological adaptation:
Phragmites australis accumulates
malate.
Salicaceae (willow)
Trees or shrubs that are separate sexes with flowers
produced in catkins.
Morphological adaptations: Populus deltoides has
adventitious roots and species of Salix have
hypertrophied lenicels, adventitious roots, and spaces
in the stem tissues that allow oxygen to reach the
roots.
Salix nigra
Wetlands Research Program Technical Report Y87-1 (on-line edition)
Corps of Engineers
Wetlands Delineation Manual
by Environmental Laboratory
http://wetland-delineation.rutgers.edu/87-wetlanddelineation-manual/
Useful supplementary information for making wetland
determinations can also be found at the following sites on the
World Wide Web:
List of wetland plants
http://rsgisias.crrel.usace.army.mil/NWPL/
Analyses of normal precipitation ranges and growing season
limits
http://www.wcc.nrcs.usda.gov/climate/wetlands.html
National Wetlands Inventory maps and databases
http://www.fws.gov/wetlands/
Table C1
Partial List of Species with Known Morphological
Adaptations for
Occurrence in Wetlands1
Species
Common Name Adaptation
Acer negundo Box elder
Adventitious roots
Acer rubrum
Red maple
Hypertrophied lenticels
Acer saccharinum
Silver maple
Hypertrophied lenticels;
adventitious roots
(juvenile plants)
Alisma spp.
Water plantain Polymorphic leaves
Table C2
Species Exhibiting Physiological Adaptations for
Occurrence in Wetlands
Carex arenaria
Carex flacca
Carex lasiocarpa
Malate accumulation
Absence of ADH activity
Malate accumulation