FUNGI AND ITS RELATIONSHIPS WITH OTHER ORGANISMS

Mutualistics RelationshipFungi and Plants: Mycorhizza, Lichen

Parasitic RelationshipFungi and Animal or InsectsFungi and Humans

MUTUALISM vs PARASITISM

Symbiosis: any situation where two different species live together.Mutualism – both partners benefit.Parasitism – only one partner benefits; typically reduces the fitness of other.Commensalism – two species live together without either harming the other, but where only one partners benefit.Mutualism and paratism were extensively studied.

MUTUALISM vs PARASITISM

MUTUALISTICS RELATIONSHIP WITH PLANTS

MYCORRHIZA“Myco” meaning fungus, “Rhiza” meaning root.Mycorrhiza is a mutualistic relationship between a fungus in the soil and a plant root. Characteristics:1) Can increase uptake of plant nutrients such as

phosphorus and nitrogen especially when there is a low concentration / insoluble form of it in the soil.

2) Can assist nutrient uptake by plants from dilute solutions.

TYPES OF MYCORRHIZA

1) Ectotropic2) Vesicular-arbuscular (V-A)3) Orchidaceous4) Ericaceous

Ectotrophic (sheating) Mycorrhiza

Typically associated with temperate trees.Ex: Amanita muscaria (fly agaric) with birch or pine.Association: Mutualistic: fungus supplies plant with NH3 and PO4

3- from soil, plant supplies fungus with carbohydrates produced during photosynthesis.

Ectotrophic (sheating) Mycorrhiza

Characteristics:1) Fungus forms highly

developed sheath around roots. Mycelial strands extend into soil.

2) Intercellular invasion of cortex to form Hartig’s net.

3) Root hair formation suppressed (mycelium functional equivalent of root hairs). Root morphology altered.

Vesicular-arbuscular (V-A) Mycorrhiza

Most widespread type of mycorrhiza.Associated with borophytes, ferns, spermatophytes (especially tropical trees). Ex: Endogone spp. with grasses.Association: Mutualistic: fungus supplies plant with NH3 and PO4

3- from soil, plant supplies fungus with carbohydrates produced during photosynthesis (same as ectotrophic mycorrhiza).

Vesicular-arbuscular (V-A) Mycorrhiza

Characteristics:1) No sheath. Fine

hyphae extend to soil.2) Intracellular

penetration of middle cortex. No Hartig’s net. Fungus form characteristics vesicles and arbuscules.

3) Root hairs present. No apparent alteration of root morphology.

Orchidaceous Mycorrhiza

Unique to orchid.Ex: Armillaria mellea (honey fungus) with Gastropodia elata.Association: Orchid parasitic on fungus.Peletons degenerate and supply orchid with sugars, vitamins and other nutrients obtained by saprophytic action of fungus outside root.

Orchidaceous Mycorrhiza

Characteristics:1) Same as V-A.2) Intracellular

penetration of inner cortex. Fungus forms characteristics coils (peletons).

3) ± root hairs.

Ericaceous Mycorrhiza

Associated with heather and related plants. Includes Boletus and monotropa (bird’s nest plant)Association: Variable: achlorophyllous plant may be parasitic on fungus (monotropa type). Alternatively, mutualistic in heather type.

Ericaceous Mycorrhiza

Characteristics:1) Variable form; loose

weft of hyphae surrounds root (heather) or definite sheath (Monotropa).

2) Intracellular penetration of outer cortex. In Monotropa a Hartig’s net may be additionally present.

3) No root hairs, no epidermal cells.

LICHENS

Mutualistic combination of an alga or blue-green bacteria (cyanobacterium) with fungus.

ORGANISMMycobiont (fungus) There are ascomycetes or Basidiomycetes

(rarely). They are ecologically obligate symbionts.

Phycobiont (alga or bacterium) These are green algae (ex: Trebouxia, 70 % of

all lichens) or blue-green bacteria (ex: Nostoc). They may be free living.

Main Features of LichensRELATIONSHIP BETWEEN ASSOCIATES

Alga (phycobiont) produces and secretes carbohydratesFungus (Mycobiont) may supply minerals to the alga.Uncertain, no experimental confirmation, phycobiont may be able to absorb its own minerals from the substrate.This association probably enables both partners to exploit habitat which would be unsuitable for either alone.

STRUCTUREThere is often a highly organised thallus, with algae forming a definite layer.

Three Types of Lichens

MORPHOLOGYCrustose: crust like, Ex: Xanthoria which is the common yellowish lichen on gravestone.Foliose: Leaf like, Ex: Parmelia which is common in woodland. Fruticose: Shrubby, Ex: Cladonia which is common on acid heathland.

Lichens survive on bare rock, tree trunks, inhospitable places.

Lichens growing on a rock.

Lichens growing on trees.

Lichen Thallus

Ecology and Applications of Lichens

Lichen killed as SO2 levels rise.

Used as indicator of atmospheric pollution. Lichens are so efficient at absorbing nutrients from the air that they can be used to monitor air quality because some kinds do not survive in polluted air.Breaking down rocks and starting the process of soil formation.Lichens or their products may be used as: Dyes (Harris tweed) Food (for reindeer herds) Antimicrobial (Usnea) Indicators (Litmus)