1. Fungal associations:
Lichens - Fungi in closely integrated association with green algae and/or blue-green algae.
Mycorrhizae - Fungi associated with exterior (ectotrophic) or interior (endotrophic) of plant roots
Endophytes - fungi associated with shoots of plants

2. Fungal associations: trees dependent on mycorrhizae
lichens - predominant ground cover in tundra

3. Lichens

4. - dual organisms Lichens
Lichens very tough - typically grow in extreme environments (arctic, hot deserts, bare rock etc.) - often dominant life form where they occur (8% of world). Consist of:-
mycobiont (fungus) - obtains water and minerals, builds shape (thallus), produces the reproductive structures.
Phycobiont (alga) - contributes photosynthate Probably more a case of balanced parasitism than symbiosis.

5. The mycobiont has two principal roles:
to protect the photobiont from exposure to intense sunlight and desiccation
to absorb mineral nutrients from the underlying surface or from minute traces of atmospheric contaminants.
The photobiont also has two roles:
to synthesise organic nutrients from carbon dioxide
in the case of cyanobacteria, to produce ammonium (and then organic nitrogen compounds) from N2 gas, by nitrogen fixation. In some ecosystems such as desert soils, tundra heaths, and Douglas-fir forests of the Pacific Northwest of the USA, lichens can provide the major input of nitrogen which supports other forms of life.

6. Lichens
Nomenclature - there are ca 20,000 sp. named after the mycobiont (500 genera)
Structure - The mycobiont forms the major part (95%) of the thallus (body) and produces any sexual spores. The photobiont exists as cells, often in layers just below the surface, within the thallus

7. Lichens The Phycobiont.
Only 24 genera of algae, either Chlorophyta (green algae) or Cyanobacteria (prokaryotes - blue-green algae). In 70% of lichens the alga is a sp. of Trebouxia.
Some algae (not Trebouxia) can be free living
some lichens have both blue-green and green algae as phycobionts in same thallus.

8. Trebouxia cells - the most common green algae found in lichens
Cells of Nostoc - a blue-green alga found in lichens.

9. Lichens Mycobiont. 98% Ascomycetes, rest Basidiomycetes.
40% of all Ascomycetes are obligate lichens.
About half have teleomorph + anamorph, half teleomorph only + small number anamorph only. Never free-living
apparently originated many times independently

10. fungus hyphae
algal cells

11. algal cells
fungal hyphae

12. Lichens Lichens grow in a variety of forms:-
crustose - thin crusts tightly attached to surfaces
foliose - leaf like protrusions attached to surface by rhizines
fructicose - bush-like branched aerial projections
squamulose - aerial structures made of small scales
leprose - loose powdery thallus

13. Crustose lichens

14. crustose type of growth

15. crustose type of growth

16. crustose lichen on bark

17. Foliose
lichens

18. Foliose type of growth

19. crustose
fructicose (reindeer moss)
foliose

20. fruticose type of growth

21. fructicose lichens

22. podetia
Squamulose type of growth

23. Lichens fungus can reproduce:-
sexually by ascospores (no algal component) - spore must ‘locate’ a suitable alga
asexually - soredia - powdery masses of alga + hyphae - isidia - finger like masses of alga + hyphae

24. Lichens Sexual reproduction.
Most lichen fungi produce apothecial ascoma (cup-shaped)
Asci form in the apothecia and release ascopores - BUT no algal component.
A few lichen fungi are basidiomycetes and produce ‘mushrooms’

25. apothecia

27. Lichens
Ascospores contain no algae - so how does the lichen reassemble ?
The fungus can grow slowly for a while without alga - grows as disorganized mass - no shape. Once it meets alga, grows as organized mass into lichen form.
needs to find an alga of correct species to survive - sometimes can last a little longer by forming temporary associations with other algae
we can only simulate reassembly in the lab when we starve both components first.

28. Lichens Asexual reproduction.
Soredia - algal cells wrapped in threads of fungus
Isidia - tiny projections from the surface of the lichen that can break off easily and grow into a new lichen.
Most lichens are very brittle when they're dry, and some depend on just plain breakage to produce fragments that, like soredia and isidia, can be blown around by wind, washed along by water, or carried off as passengers on insects or birds.

29. Isidia
Soredia

30. Lichens lichens produce many unique compounds weak phenolic acids
provide resistance to grazing
UV resistance?
Important in sp. identification
some antibiotics,
fungal genes produce these compounds but only active when alga present !

31. Lichens
Lichens grow slowly (only 5-10% of mass is alga and they are often in very dry situations) but are extremely resistant to effects of drought, floods, heat or cold.
Lichens have great longevity - can live for thousands of years.

32. Lichens
Lichens - are a very important ecological component in extreme habitats
eg in tundra - - dominant lifeform - provide grazing (‘reindeer moss’)
weathering of bare rock ---> soil
often absent from agricultural or urban environments (sensitivity to pollution)

33. Montreal area showing correlation between SO2 pollution (below) and lichen presence (red dots on map at left)
Lichenometry (studies of lichen growth rate) used in geology (how long since rocks emerged from ice) and pollution.
Lichens have no roots - depend on rain - so ultrasensitive to rain borne pollution

34. Lichens and Pollution.
Lichen fungi are extremely efficient in accumulating nutrients from trace levels in the atmosphere and so are especially sensitive to pollution.
An extreme demonstration of this is the ability of lichens to accumulate radioactive isotopes from the environment.
Following the Chernobyl disaster, the lichens (mainly Cladonia rangiferina, the "reindeer moss") of northern Scandinavia accumulated so much radioactivity that reindeer feeding on them were considered dangerous for human consumption.

35. Wolf lichen" (Letharia vulpina) - the most widely used dye lichen for native peoples in North America,
Oakmoss lichen - important in fine perfumes (S-central Europe)
Usnea filipendula traditionally used as medicine for wounds - has been found to contain some potent antibiotics)
Uses of Lichens

36. Lichens and Wildlife NESTS
The golden plover uses Thamnolia vermicularis in its nests. More than 50 species of birds in North America known to use lichens in nest building.
Flying squirrel nest made entirely of Bryoria
CAMOUFLAGE - lacewing insects covered in lichen
FOOD. - Witch's hair lichen blows off trees - helps black-tailed deer survive when other forage under snow
FOOD. Mountain goats, Caribou eat lichens.
Lichens and Wildlife

37. A case of reverse lichenosis or just a universal parasite
A case of reverse lichenosis or just a universal parasite ? The large marine brown alga, Ascophyllum nodosum always contains the fungus, Mycosphaerella ascophylli

38. 2% of lichens have fungi belonging to the Basidiomycetes and so produce mushroom-type fruiting bodies. e.g. Omphalina ericetorum
Multiclavula corynoides

39. Follow-up to Lecture Read Chap 7
View Fifth Kingdom CD/ Web page (Chap 7)
Review these lecture notes on Web
know main features of Lichens
review terms -
mycobiont; photobiont; soredia; isidia
5 growth forms (crustose etc.)