Lichens are a mutualism formed between fungi and various groups of algae. The importance of . Another problem that lichens face is being eaten by animals. Volume , Issue 6, June , Pages Mycological The fungus ( mycobiont) usually comprises most of the lichen, while the photosynthetic algal or . Discusses parasitic and mutualistic relationships of fungi. This fungus is a lichen, providing nutrients to the tree. The lichen gets sugars from the plant. They are the major cause of disease in agricultural plants. Fungi also.
These two components exist together and behave as a single organism. When two organisms live together in this way, each providing some benefit to the other, they are known as symbionts.
The alga, because it is a green plant, can photosynthesize and provide energy for the lichen. The fungus contributes to the relationship by obtaining water and minerals and by protecting the algal cells from desiccation.
Together the fungus and the alga make up what is known as the lichen thallus. The color and growth form of the thallus is used to group and classify the lichens. The most common species of lichens on trees tend to be a gray-green color, but other species may be orange, yellow, slate blue, or black. There are three major growth forms of lichens: Foliose lichens have leaf-like lobes. These are the gray-green structures that can often be seen growing on tree trunks or branches.
They are slightly raised and can grow and coalesce with other lichen thalli, covering several inches or more of bark. If moistened, they become somewhat rubbery and can be removed. Soredia are small bundles of algae held together by fungal hyphae. They are small enough to be carried by wind yet guarantee the presence of both partners.
Mutualisms between fungi and algae
The illustration above left shows a young thallus of the foliose lichen Peltigera didactyla. In this species the upper surface becomes dotted with soralia, special structures for the production of soredia.
In the photograph, the soralia have released granular masses of soredia. The other photograph above is a highly magnified view of isidia, small coral-like branches containing both mutualists that can break off and drift to a new habitat. The lichen in the picture is Xanthoparmelia conspersa, a common lichen on exposed rock in New Brunswick.
Lichen habitats One of the fascinating aspects of lichen biology is the ability of these organisms to occupy habitats that would be totally in inhospitable to other organisms. Thus we can find them growing on the ground in deserts, on the sides of dry rock, hanging from the branches of trees and and even growing on the backs of turtles. They are nearly as easy to find and study in the middle of winter as during the warmer months. The first of the three photographs above was taken in Saskatchewan, out in an open prairie.
The rock in the forground is the highest point in the immediate area; animals sitting there get a panoramic view of the grassland and all that is taking place there. It is a favourite place for birds, especially birds of prey waiting for a mouse or vole that might be moving through the grass. The orange lichen is a species of Xanthoria that thrives on nitrogen-rich bird droppings left on the rock. Similar species of Xanthoria, as well as members of the related genus Caloplaca, can be found on our seacoast on rocks frequented by gulls and cormorants.
The second of the two pictures above is of White Horse Island, a small island in the Bay of Fundy supporting large colonies of nesting birds. The white colour of the rock is due to a thick layer of bird droppings; the orange material is a species of Caloplaca. 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. 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.
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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.
MUTUALISMS BETWEEN FUNGI AND ALGAE
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.
Fungi Symbiosis ( Read ) | Biology | CK Foundation
In return the fungus has access to carbohydrates and other nutrients within its protective environment. Garbary and colleagues at St.Lichen: Two Living Things In One - Biology for Kids
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.