Lichens
Lichens on Heard Island
A lichen is a plant formed from the symbiotic association of certain fungi and (usually) green algae. Lichens with associated cyanobacteria are also known. Lichens occupy many different habitats, often in extreme environments.
Three main types of lichens exist in Antarctica. Crustose lichens, which form a thin crust on the surface of the substrate they grow on; foliose lichens, which form leaf like lobes; and fruticose lichens which have a shrubby growth habit.
Lichens have very slow growth rates. In the most favourable of conditions in the Maritime Antarctic, growth rates reach 1 cm or more per 100 years. In the harsher environment of the Continental Antarctic, growth is much slower, and may be as little as 1 cm per 1, 000 years for Buellia frigida in the McMurdo Dry Valleys region.
Lichens can be found growing in most areas of the Antarctic capable of supporting plant life. Currently 4 general distributional patterns of lichens are known. These are: species confined to the Maritime Antarctic; those found in the Peninsula and extending to the Lesser Antarctic; those with a Circum Antarctic distribution; and those with very disrupted or Disjunct distribution patterns.
The Maritime Antarctic lichens are restricted to the northern Peninsula and nearby islands. Many of the lichens found in Antarctica are restricted to this area. A number of the lichen species found here are also found in the subantarctic islands and the colder parts of the southern continents, and may represent a southern extension of these populations. This area has the greatest species diversity in Antarctica.
Lichens have been collected from as far south as 86° 30'.
Xanthoria elegans (orange) and Buellia frigida (black)
| Many lichens have been formerly described as Antarctic endemic species. However, a large number of these are now considered as identical to other species and far fewer lichens now appear to be endemic to Antarctica. Many Antarctic lichens have a bipolar distribution, that is they are found in both the Arctic and the Antarctic, but not in areas in between.
Lichens have a number of adaptations that enable them to survive in Antarctica. They are able to exhibit net photosynthesis while frozen at temperatures as low as -20° C. They can absorb water from a saturated atmosphere when covered by snow. Additionally, snow cover affords protection from the elements and most growth appears to occur when they are buried beneath at least a thin protective layer of snow. They can survive long unfavourable periods of drought in a dry and inactive state. In continental Antarctica, many lichens are able to absorb water vapour from snow and ice.
Some aspects of climate change are expected to have little effect on lichens. It has been shown that increased levels of UV radiation will not damage lichen species (high UV levels actually increase net photosynthesis at low CO2 concentrations) and that rises in CO2 levels will increase net photosynthesis. Likewise, rising temperatures are also expected to enhance lichen growth as many Antarctic lichens are living at temperatures well below their physiological optimum requirements. However, because it is difficult to predict the effect climate change will have on free water availability, it is unknown how global climate change will ultimately affect the lichens.
Lichens are also quite sensitive to atmospheric pollution from distant sources. Traces of DDT and organochlorines have been detected in Antarctic lichens. Radionuclides, possibly of anthropogenic origin, have also been shown to accumulate in Antarctic lichens, bryophytes, algae, and soil.
Links
Australian Antarctic Science (AAS) relating to Antarctic Lichens
Australian Antarctic publications relating to Antarctic Lichens
See more information on the Australian Antarctic Research Biology program
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