University of Western Ontario

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1 University of Western Ontario
Fungal Ecology March 2008 Greg Thorn Department of Biology University of Western Ontario London, Ontario, Canada

2 Outline and Coverage Chapters in the Fifth Kingdom, 3rd edition:
Chapter 11 (March 17): Fungal Ecology Chapters (March 19): Fungi Exploiting Microscopic Animals, and Mutualistic Symbioses Between Fungi and Animals Lab (March 19 / 26): Nematode-destroying fungi

3 Outline for March 17 Importance of Fungi in Terrestrial Ecosystem Processes Fungi drive nutrient cycles The connectedness of ecosystems Topics in Fungal Ecology: Succession in wood decay and dung fungi Amphibious fungi and freshwater streams [Aero-aquatic fungi - see text] Fungi in danger of extinction [Fungi as bioremediators - another day]

4 What is Fungal Ecology? Ecology is the scientific study of the interrelationships among organisms and their environment. Fungal ecology involves a biotic component (the other organisms, including other fungi, that fungi interact with) and an abiotic component (space, nutrients, and other environmental resources that fungi need to grow and reproduce).

5 The Biotic Component of Fungal Ecology
There is probably no terrestrial organism that a fungus does not interact with in some way - use for food, as a means of dispersal, or as a home. Fungal interactions with man, his crops and livestock involve medical and veterinary mycology (April) and plant pathology (next week). On Wednesday we will discuss predatory and mutualistic associations between fungi and invertebrates and other animals, and predatory associations between fungi and bacteria.

6 The Abiotic Component of Fungal Ecology
There is probably no naturally-occurring organic compound, and very few man-made ones, that can not be used as food or degraded by fungi. [Fungal physiology; biodeterioration research] Fungi dominate terrestrial ecosystems, but true fungi are a minor component of most marine ecosystems. [Labyrinthula in eel-grass] Today we will discuss the importance of fungi in terrestrial ecosystem processes, and a few interesting topics in fungal ecology.

7 Soil Food Web Overhead (needs a few more boxes and arrows!)

8 Review: The 3 most important biological processes on Earth are
Photosynthesis Respiration Decomposition There are basically 3 modes of fungal nutrition: Saprobic/saprotrophic (decomposers) Mutualistic Predatory and parasitic

9 Review of ecological terms
Symbiosis: association of two different organisms living in close physical contact Parasite: an organism that derives part or all of its food from another Pathogen: an organism [or abiotic agent] that causes disease Mutualism: association of two different organisms that is beneficial to both partners Saprotrophic, saprobic: feeding on dead matter (saprophytic is also used, but implies that the organism is a plant which feeds on dead matter)

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11 (but there are many more)
Unquestionably, the two most important functions of fungi in ecosystems are Decomposition and nutrient cycling Mycorrhizal symbioses (but there are many more)

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14 Why are fungi great decomposers?
Whereas bacteria are the primary decomposers of dead animal matter, fungi are the decomposers par excellence of the other 90% of the organic wastes in terrestrial ecosystems. This is because the fungi, especially the Agaricomycetes, are the best equipped with enzymes such as laccases, lignin peroxidases, manganese peroxidases, and cellulases for degrading lignocellulosic plant wastes. In addition, their hyphal growth form allows them to penetrate solid substrates such as wood and to communicate between distant resource units.

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16 More on decomposers Decomposer fungi lacking enzymes to degrade intact lignin chew away at the cellulose exposed as the lignin is removed by other fungi, and on the breakdown products of lignin, until much of the original plant biomass is respired as CO2. The remaining recalcitrant phenolic fractions become complexed with fungal and microbial cell wall or sheath materials and then add to the humic fraction of soil. During the decomposition process, many or most fungi act in consortium with other fungi, protists and prokaryotic microbes, and sometimes also animals.

17 Rock-eating fungi? Some ectomycorrhizal fungi etch micropores in feldspar, hornblende and other soil minerals by release of organic acids, and then use and transport these nutrients to their mycorrhizal host plants. Decomposer fungi may also attack rocks for their mineral nutrients, especially P; lichen fungi certainly do this too.

18 Fungi drive and connect nutrient cycles
Fungi are important in making connections in ecosystems across time and space and among trophic levels because of the hyphal growth form of filamentous fungi and because many fungi are simultaneously decomposers and mutualists or predators and saprotrophs.

19 How connected are ecosystems?
Abiotic factors (parent material, climate, etc.) and biotic factors (plant community, fungal community, and invertebrate community, etc.) combine to determine soil type, which determines plant community, which determines fungal community … Humans have significantly altered abiotic and biotic factors that affect ecosystem composition and function

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21 Succession in wood decay and dung fungi
In both cases, the resource base declines during succession - the fungi (and other inhabitants) use it up. Succession is a sum of life history strategies (reproduction, dispersal, growth rates, substrates used as food) and competition among species. Succession in fungi may be visible or invisible

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23 The polypore Irpex lacteus is among the first fungi to appear on dead hardwood

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28 Amphibious fungi and freshwater streams

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33 Fungi in Danger of Extinction (?)
In Canada, 25 extinct or endangered birds, 12 terrestrial mammals, 10 marine mammals, 50 vascular plants, 0 fungi In areas where fungi are better known, there have been disturbing trends towards loss or increased rarity of selected species Understanding why is in itself a good lesson in fungal ecology

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36 Some rare polypores in North America
“Fuzzy Sandozi” (Bridgeoporus nobilissimus), found on > 1 m diam Abies, etc., in only 6 sites in Washington and Oregon Globifomes graveolens, known in Canada only from historic collections from Rondeau Polyporus pseudobetulinus, discovered in North America in 1987, otherwise known from Siberia and northern Europe (?)

37 Wednesday … Fungi associated with wee beasties