Lichens & Mycorrhizae

Outline

Lichens

A symbiosis between algae and fungi

alga -- phycobiont -- usually the chlorophyte Trebouxia (also the cyanobacterium Nostoc)

fungus -- mycobiont -- usually an ascomycete (also basidiomycetes)

Ecology

tolerant of harsh conditions

important as pioneer species in primary succession -- soil formation

N-fixation in some forests

Economic importance

food, fodder

dyes

in perfumes

Morphology

types

• crustose
• foliose
• fruticose

anatomy

• cortex (upper and/or lower)
• medulla
• algal layer
• rhizines

Reproduction

• sexual or asexual fungal spores
• soredia
• isidia

Nutrition -- parasitism or mutualism?

fungus receives cabohydrates from alga (90%)

appresioria or haustoria

some lichens have heterocystous cyanobacteria (Nostoc, usually) as primary or secondary phycobiont

alga releases 95% of N to fungus

can be an important N source for forest ecosystems

 parasitism or mutualism?

Mycorrhizae

A symbiosis between fungi and plants

fungus -- may be from all 4 divisions

plant -- everything from liverworts to flowering plants (an ancient association)

four kinds:

Ectomycorrhizae

mainly on temperate forest trees, w/ basido- and ascomycetes

structure -- sheath around cells of roots

function -- fungi get carbohydrates, plants get inorganic nutrients (esp. P)

ecology

storage of episodically available nutrients

Endomycorrhizae

Vesicular-arbuscular mycorrhizae (VAM)

80% of all vascular plants, w/ zygomycetes

structure -- vesicles and arbuscules, penetrate host cells

function -- fungi get carbohydrates, plants get inorganic nutrients (esp. P)

Orchid mycorrhizae

plant is parasitic on fungus

orchid seeds won't germinate w/o fungus

Heath mycorrhizae

 

Vocabulary

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