Chapter 13: Ecosystem mycology: saprotrophs, and mutualisms between plants and fungi
In this Chapter on ecosystem mycology we cover fungi as saprotrophs, and the mutualisms between plants and fungi, concentrating on fungi as recyclers that can make the earth move. Fungi also cause food contamination and deterioration through their formation of toxins, although some of these, like statins and strobilurins, are exploited commercially for our own practical purposes.
The ability of fungi to degrade wood makes them responsible for the decay of structural timber in dwellings, but on the other hand enables them to be used to remediate toxic and recalcitrant wastes. A downside, though, is that wood decay fungi release chlorohydrocarbons, potent greenhouse gases, to the atmosphere and thereby potentially contribute to global warming.
Interactions with plants dominate the rest of the Chapter. We describe all types of mycorrhiza: arbuscular (AM) endomycorrhizas, ericoid endomycorrhizas, arbutoid endomycorrhizas, monotropoid endomycorrhizas, orchidaceous endomycorrhizas, ectomycorrhizas and ectendomycorrhizas. The effects of mycorrhizas and their commercial applications, and the impact of environmental and climate changes are also discussed. Finally, we introduce lichens, endophytes and epiphytes.
Evidently, fungi contribute to a broad and vibrant network of interactions with all members of the plant, animal, and bacterial kingdoms (Prosser, 2002). Because of their unique attributes, fungi in particular play vital roles in most ecosystems.
- They act as mutualists (forming symbiotic associations in which all partners benefit) of virtually all plant species, and a great many animals; but arguably the most important of these are the lichens, which are usually associations between a fungus and a green alga, and the mycorrhizal association between plants and fungi. Most plants depend on mycorrhizal fungi for their survival and growth, the fungus taking photosynthetic sugars from the host in return. The benefits of mycorrhizas to plants include efficient nutrient uptake, especially phosphorus, because the fungus extends the nutrient-absorbing surface area of the roots, but water uptake through the mycorrhiza enhances plant resistance to drought stress, and the mycorrhiza provides direct or indirect protection against some pathogens (see below).
- Parasitic and pathogenic fungi infect the living tissues of plants, animals, and other fungi, causing injury and disease that adds to the selection pressure on their hosts (see Chapters 14, 15 and 16). Even fungal plant pathogens have a positive effect on the natural environment by enriching its species structure. Plants killed by disease provide organic matter for nutrient cycling organisms; dead branches or heart rot in live trees create habitats for cavity nesting animals, while gaps in stands of dominant plants caused by disease allow development of other plants, contributing both to species diversity and diversity of food for animals, from insects to elk.
- Fungi are the saprotrophs that perform the decomposition processes that contribute to organic and inorganic nutrient cycling. Clearly, fungal decomposition of dead organic matter, be it wood or other plant litter, animal dung, cadavers and bones, is an essential ecosystem function because it maintains soil nutrient availability (see below). But there is another significant contribution along the way: fungi that decay wood soften the timber sufficiently to allow small animals (birds, reptiles, amphibians, insects, mammals) to make burrows and nests.
- Fungal products aggregate soil particles and organic matter, improving drainage and aeration; and by so doing they create habitat diversity for many other organisms (see our discussion of glomalin at the end of the On the far side section of Chapter 6 (CLICK HERE to view the page).
- Fungi serve as both prey and predators of many soil organisms, including bacteria, other fungi, nematodes (Yeates & Bongers, 1999), microarthropods, and insects (Cole, Buckland & Bardgett, 2008; Gange, 2000) (see Chapter 15).
- Mushrooms and truffles are consumed by many animals including large mammals like primates, deer, and bears, and many small mammals rely on mushrooms and truffles for nearly their entire food supply. The fungal mycelium is an equally important nutritional resource for many microarthropods (see the Fungi in food webs section of Chapter 11; CLICK HERE to view the page).
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Ordering details: Moore, D., Robson, G.D. & Trinci, A.P.J. (2011). 21st Century Guidebook to Fungi. Cambridge, UK: Cambridge University Press. ISBN: 9780521186957.
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Updated December 23, 2016