Biological Adaptations to the Wetland Environment

Two problems that biota face in wetlands

1. Anoxia - depletion of oxygen in soil and waterin a flooded wetland

2. Salt - changes osmotic potential and whenconcentrations 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 containenzymes other than ADH and are not poisonedby alcohol accumulation. MDH that producesmalate is a common example of an enzymeutilized for anaerobic respiration in wetlandplants.

Aerenchyma and adventitious root developmentabove anaerobic zone are stimulated by hormoneauxin that triggers growth of adventitious roots. Newgrowth releases ethylene that accumulates in rootsunder anaerobic conditions such as waterlogged soils.Ethylene stimulates the formation of cellulase thatopens 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 lenticelsthat are more numerous on stem increase

oxygen uptake during inundation

rhizosphere oxidation - oxygen diffusing from theroots reacts with potentially toxic reduced ionsforming oxidized forms that precipitate out of therhizosphere (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.

Photorespiration when stomates Close produces a 2-C compound that cannot be used to make sugar.

C-4 photosynthesis keeps carbon dioxide concentration high so photorespiration does not occur.

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 andobtain nitrogen from exoskeletons.

3) phosphorous - availability increases in water-logged 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 in nonflood seasonby delayed flowering

2) hydrochory. Fruits or seeds adapted tofloating and fungal resistant.

3) vivipary. Seeds germinate on the plants andseedlings drop into the water. Example:mangroves

4) prolonged seed viability Ex bald cypress seedsremain viable for 20 years or more and germinateduring infrequent periods when soil is dewatered.

5) flood tolerant seeds and seedlings. Somespecies can germinate underwater or haveseedlings that survive inundation. For exampleashes have seedlings that can survive inundation.

Animals have six major adaptations to anoxia.

1) Modifications for gaseous exchange.Examples include gills and parapodia.

2) Mechanisms to improve the oxygen gradientacross a membrane. For example, cilia movingwater over gills or animals swimming to oxygen-rich water.

3) Better circulatory system.

4) Use of more efficient respiratory pigments inblood and/or higher concentrations of thesepigments. For example, mollusks havehemocyanin (copper based) while the annelidshave more efficient hemoglobin.

5) Low oxygen behaviors such as reduced motility orclosing a shell.

6) Increased metabolism or heart pumping rates.

Three Major Adaptations to Salt in Animals

1) nephridia help retain water and eliminatesalts in concentrated urines.

2) salt secreting glands.

3) Reproduction with large numbers of larvae thatare distributed widely and can tolerate a variety ofsalinity changes so that some survive.

Plants are wetland indicators because of theiradaptations and demarcate wetland boundaries.

Some common angiosperm plant familiesand a few examples of species found in

North-central Texas Wetlands

Aceraceae (maple)

Trees or shrubs with reduced flowers that producewinged fruits called samaras.

Morphological adaptations: adventitious roots,hypertrophied lenticels.

Acer negundo

Alismataceae (arrowhead)

Herbs with linear to lanceolate or arrowhead-shapedleaves with three sepals and petals as well as manystamens 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 aslight increase in metabolism under anaerobicconditions as compared to non-wetland species thathave large increases.

Cupressaceae (cypress or cedar)

Trees or shrubs with scale-like leaves and smallwoody cones.

Morphological adaptations: buttressed trunks andpneumatophores.

Cyperaceae (sedge)

Grasslike herbs often having edgedstems and a single bract coveringeach of its many reduced flowers.Most are in wetland habitats.

Morphological adaptations: inflatedstems and leaves

Physiological adaptations: Somehave been shown to have malateaccumulation and lack of ADH activity.

Cyperus strigosus

Carex

Juncaceae (rush)

Grasslike herbs with round stems and basal, tuftedleaves as well as six papery flower parts. Most are inwetland habitats.

Morphological adaptations: inflated stems and leaves

Physiological adaptation: Juncus effusus can growroots under very low oxygen conditions and does nothave ADH activity.

Lythraceae (loosestrife)

Herbs with 4-6 crumpled petals on the edge of afloral cup (crape-myrtle is a cultivated shrub in thisfamily).

Physiological adaptation: Lythrum salicaria has noADH activity.

Nymphaceae (water lily)

Herbs with floating round or heart-shaped leaves andlarge, showy, many-parted flowers. All are inwetland 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 andreduced flowers enclosed intwo bracts.

Physiological adaptation:Phragmites australis accumulatesmalate.

Salicaceae (willow)

Trees or shrubs that are separate sexes with flowersproduced in catkins.

Morphological adaptations: Populus deltoides hasadventitious roots and species of Salix havehypertrophied lenicels, adventitious roots, and spacesin the stem tissues that allow oxygen to reach theroots.

Salix nigra

Wetlands Research Program Technical Report Y-87-1 (on-line edition)Corps of EngineersWetlands Delineation Manualby Environmental Laboratory

http://www.wes.army.mil/el/wetlands/pdfs/wlman87.pdf

Useful supplementary information for making wetland determinations can also be found at the following sites on the World Wide Web:& Hydric soils definition, criteria, and listshttp://www.statlab.iastate.edu/soils/hydric/& National list of plant species that occur in wetlandshttp://www.nwi.fws.gov/bha/& Analyses of normal precipitation ranges and growing season limits http://www.wcc.nrcs.usda.gov/water/wetlands.html& National Wetlands Inventory maps and databaseshttp://www.nwi.fws.gov/

Table C1Partial List of Species with Known Morphological Adaptations forOccurrence in Wetlands1Species Common Name AdaptationAcer negundo Box elder Adventitious rootsAcer rubrum Red maple Hypertrophied lenticelsAcer saccharinum

Silver maple Hypertrophied lenticels; adventitious roots (juvenile plants)Alisma spp. Water plantain Polymorphic leaves

Table C2Species Exhibiting Physiological Adaptations for Occurrence in Wetlands

Carex arenaria Malate accumulationCarex flacca Absence of ADH activityCarex lasiocarpa Malate accumulation