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Biological Adaptations of the Wetland Environment. Chapter 6. Organisms living in wetland areas experience greater stresses than do wither aquatic or terrestrial organisms. Wetland soils often lack oxygen. Long periods of flooding and water fluctuations increase harshness of environment.
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Organisms living in wetland areas experience greater stresses than do wither aquatic or terrestrial organisms. • Wetland soils often lack oxygen. • Long periods of flooding and water fluctuations increase harshness of environment. • Some wetlands exposed to various levels of salinity.
Adaptive Strategies • Organisms in such conditions can adapt to stress by either tolerating or avoid it. • Tolerators (resistors) adapt survival mechanisms allowing them to live with the stress efficiently. • Regulators adapt in such ways so as to avoid the stress. • Unicellular organisms (like bacteria) have fewer options in adapting than multicellular organisms.
Unicellular Adaptations • Bacteria are mainly found in soil and thus their principle adaptations will involve anoxia (no oxygen in the soil) • Oxygen used as a source of electron acceptors. • Bacteria start to use other ions as acceptors when oxygen lacking. • Desulfovibriodesulfuricans and other becteria from this genus use sulfur as the electron acceptor letting off a rotten egg smell.
Plant Adaptations of flooding • Hydrophytes (plants which can tolerate flooding) have many strategies to respond to anoxia. • They sometimes change their physiology. • Many plants alter their morphology (change their structure). • Plants also can change the way they produce and distribute their seeds.
Morphological Strategies • Aerenchyma- Most all wetland plants employ this strategy. Aerenchyma are air spaces in roots and stems which allow oxygen from the air to diffuse down to the roots. • Such spaces take up only around 5% of the root volume in normal plants but up to 60% root volume in hydrophytes. • Aerenchyma is a regulation strategy.
Adventitous roots- these roots develop just above the flooded area. • Stem Hypertrophy- You can see these often in trees around here. The lower part of the tree trunk bulges out a bit. This wood has larger cells and is less dense. • Stem Elongation- One way to adapt to rising levels of water is to rapidly grow the stem to make sure the leaves will be above water level before future flooding.
Tap roots are seldom seen in wetlands and instead, plants form shallow root systems to capitalize on the increased availability of oxygen at the surface level. • Some plant use prop roots. Prop roots contain lenticels, which are small pores. • Pneumatophores are the “knees” you often see with cypress trees around this area. These knees have many lenticles in them. They act to increase oxygen flow to the roots. When you find these in a dry area, you know it was once flooded.
Physiological Adaptations • Some water lilies are able to send oxygen from the leaves, through the stem, and into the roots through a pressurized system. • As some of the older leaves lose their ability to be pressurized, they become vessels for the gas returning which carry methane produced by the roots.
Whole Plant Strategies • Plants will spend much energy to ensure survival of its species. Subsequently, plants and wetlands develop strategies to ensure seed survival. • The can change the time of their flowering to time seed production to a non-flood time. • They produce seeds which can float until they run aground • They simply produce a large number of seeds
Salinity Adaptations • Water follows solutes, like salt. Therefore, salt water will typically cause the diffusion of water out of a plant and into the salt water around it. • As a consequence, plants living in saline conditions have created barriers to prevent the entry of salts or mechanisms to excrete them. • Another adaptation is through C4 photosynthesis.
Salt Exclusion- The root periderm and exodermis in some roots can function as a barrier to salt uptake. • Salt Secretion- some plants that take up salt, like marsh grasses, have the ability to excrete salts through special glands in the leaves.
Animal Adaptations to Salinity • Many animals in saline environments are osmoconformers, meaning that they keep their internal solute concentrations similar to that of the environment thereby preventing water from moving out of their cells. • More complex animals possess a means of excreting excess sodium through adapted kidneys, gills, or other organs.
