What Are Lichens?
Lichens are a mutualism formed between fungi and various groups of algae. The photobiont and its relationship with the phytobiont are the same as in M. The fungus benefits from the symbiotic relation because algae or cyanobacteria produce food by photosynthesis, which is utilized by fungus. The tiny lichen is a critical part of the food chain, but how do algae and fungi work together to form these symbiotic organisms?.
Lobaria pulmonaria, lungwort are used for the diseases of lungs respiratory diseases and T. Parmelia is useful against epilepsy. Usnea species are good against urinary diseases. Xanthoria sp is used in jaundice etc Some lichens possess anticarcinogenic properties.
Symbiosis in lichens
The lungwort lichen is used in tanning, in perfumery. The cell walls of the fungi of certain lichens contain colouring matters.
Species of Rocella and Lecanora yield a most important colouring matter known as Orchil or Cudbear. This is used in colouring woolen and silk fabrics. It is also used for manufacturing litmus papers which are used in laboratories for acid and base identification. It is obtained from Roccella montagnei. In Russia and Sweden, lichens are used for the production of alcohol.
Some lichens are harmful to industrial products because they cause considerable damage to glass surfaces and marble stones due to etching. Ecological Importance of Lichens: Lichens Contribute to Soil Formation: Lichens thrive in undisturbed sites where nothing else will grow.
They grow on rocks, barren soil and the bark of dead or live trees. They are not parasitic when they grow on trees, they just use the tree bark as a home.
They enrich the soil by trapping water, dust, and silt. When lichens die they contribute organic matter to the soil, improving the soil so that other plants can grow there. They release carbonic and oxalic acid which leads to weathering of the rock and it leads to formation of soil.
This process is called pedogenesis. Due to their association with algae, they are able to convert nitrogen in the air into nitrates, which they need for their growth.2:00 PM - Lab Assistant सामान्य विज्ञान by Shipra Ma'am - Day #20 - Algae, Fungi, Lichens
Conversion of atmospheric nitrogen impacts the ecosystem because when it rains, nitrates are leached from lichens for use by nearby soil-based plants. Thus they make soil fertile. Lichens Need Clean Air: Although they are tough and can survive in extreme climates, including extreme heat, cold and drought, they are sensitive to air pollution.
Because they are so pollution-sensitive, some scientists use them to assess the air pollution coming from industrial plants and urban areas. They absorb everything from the air, including carbon dioxide and heavy metals. Scientists can extract the toxic compounds from lichens and determine the level of air pollution in a given area. The dying of lichens at a site is an early warning sign of harmful pollution.
The gravestone at left marks the resting place of Roland ThaxterProfessor at Harvard University and brilliant mycologist, known in particular for his monumental studies on the Laboulbeniales. Beside Roland's grave is that of his brother Karl.
Lichens : Symbiotic Relation Between Algae and Fungi
Both gravestones have become colonized by lichens and are now difficult to read. Click on the photograph to get an enlarged version of Roland's gravestone Another interesting thing about our coastal lichens is that some of them are highly tolerant of salt, a substance that is toxic to most fungi, including lichenized ones. The picture at right depicts some coastal rocks on the Bay of Fundy near Saint John.
At the bottom of the picture are bunches of brown algae, mostly Fucus vesiculosus and Ascophyllum nodosum, commonly called rockweed. These rockweeds grow in areas along the shore where they will be immersed in seawater, at least at high tide. At the very top of the rock is a patch of orange, probably Xanthoria parietina. In between is a black zone consisting of the custose lichen Hydropunctaria maura. Hydropunctaria maura can grow where it is periodically immersed in seawater but is also able to grow in an area just above that where it receives only splash from waves.
This "black zone" occupies an area that often goes for days or even weeks without immersion in seawater but will eventually get splashed. This is a tough place to live: Just the place for a lichen! The picture at right depicts yet another species of Verrucaria mucosa, a close relative of H.
In fact, it releases its ascospores when it is above the water and thus depends upon being exposed to air. However, it does not grow in the upper areas of the tide like H.
In the picture V. On parts of the rock that have dried it is harder to see but you may notice that it is slightly green, revealing the presence of the photobiont. The red spots are the alga Hildenbrandia polytypa, similar is size and growth habit to V.
The last picture again shows Verrucaria mucosa, this time growing under water at high tide. Note that even this lichen has its limits; most of the rocks in the picture have no lichens at all. This may be because the rocks are too small and may be moved by currents as the tide ebbs and flows or it may be that their surfaces are unsuitable for lichens.
Another problem that lichens face is being eaten by animals. Many contain acids and other compounds that make them unpalatable to animals but V. Notice the large rock above the one with lichens on it. On its surface is a small snail called a periwinkle.
Some periwinkles, notably the rough periwinkle, eat V. This has not happened here yet but there are in fact several periwinkles present, as well as the white barnacles and a mussel. How many periwinkles are here? Not many at first glance, but you might be surprised.
Click on the picture to get an enlarged view and see how many periwinkles you can count. One of the more intriguing mutualisms found in our region is the one between the brown alga Ascophyllum nodosum and the fungus Mycophycias ascophylli. Ascophyllum nodosum, commonly called rockweed, occurs in the intertidal zone where it is left exposed to the air when the tide goes out.
Mycophycias ascophylli, a member of the lichen-forming order of fungi Verrucarialesgrows within the body thallus of A. In return the fungus has access to carbohydrates and other nutrients within its protective environment. Garbary and colleagues at St. Francis Xavier University in Nova Scotia have studied this mutualism in detail and have shown that the fungus not only forms relationships with the rockweed but also seems to form a mutualism with Polysiphonia lanosa, a common epiphyte found attached to the A.
At far left is a thallus of A. You may wish to look further back on this page to see the habitat photo of A. The next picture shows a detail from the first panel.
The small almond-shaped structures along the stem are receptacles. Each receptacle bears a number of conceptacles, structures that release sperm and egg into the ocean each spring.
These are seen as bumpy areas in the second photo but in the third more highly magnified panel they can be seen more easily and reveal the pores through which the sperm and egg escape.
The next panel is even further magnified and the conceptacles are even clearer. In this panel it is also possible to see tiny black dots, resembling grains of pepper; these are the perithecia fruiting bodies of Mycophycias ascophylli.
The blue box drawn on around one of these leads to the next photograph, taken with a compound microscope, showing a detailed view of one perithecium partially submerged in the receptacle. The perithecia contain asci and ascospores.
The last panel shows one ascus containing eight 2-celled ascospores. The ascospores are not very clear in this picture but are nevertheless nearly mature. In our region Ascophyllum nodosum releases its sperm and eggs in late May.
On a warm day at low tide these tiny cells ooze out of the conceptacles like toothpaste out of a tube. When the tide comes in they are released into the water.
Lichens : Symbiotic Relation Between Algae and Fungi
The sperm, released in numbers large enough to colour the water orange, swim activly in search of eggs and attach to them when they find one. Eggs can be observed spinning wildly, powered by hundreds of sperm attached to their surface.
Finally one sperm succeeds in fertilizing the egg, which then sinks to the bottom to grow into a new plant.
At the same time sperm and eggs are being released the asci of Mycophycias ascophylli shoot their spores into the air. It is likely that these spores are able to colonize the newly developing plants but the details of this stage of development are still not very well understood.