Fungi & ecosystems

CONTENTS

Fungi & ecosystems

The importance of fungi to ecosystems

Leccinum aurantiacum an ectomycorrhizal fungus ©Tomas Čekanavičius

Fungi (mushrooms and toadstools) help maintain our ecosystem in balance by continuing the job they have done for many millennia. You’d be forgiven for thinking that all forms of fungi are parasitic. You may even be shocked to hear that the world of plants, particularly trees, is extremely dependent on fungi!

If we go back some 460 million years, when plants first evolved, we see that they evolved alongside fungi and in so doing developed an important symbiotic relationship (called a "mycorrhizal relationship").

Today it is estimated that less than 10% of plants and trees could survive as they do without mycorrhiza assistance, and if plants and trees couldn’t survive this would impact heavily on our ability and that of other organisms to survive on Earth.

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What is the mycorrhizal relationship?

Fly agaric Amanita muscaria © Jennifer Hope-Morley

You may have noticed that certain fungi only grow under (or even on) specific species of tree or near certain species of plant. This is because both the fungal species and the plant or tree species require similar environments. Because of this a mycorrhizal relationship has been built up over the millennia between the two species. This means that these species cannot exist (or would find it very difficult to exist) without the other.

While fungi naturally break down leaf litter, dead wood and other decaying organisms as part of their feeding process, fungi also play an important role in assisting the growth and development of plants and trees – even those in generally dry environments such as Eucalyptus species found in Australia. Research has discovered that this relationship is particularly important in aiding the growth of healthy trees.

The mycorrhiza is a direct association between the fungus and the roots of plants or trees, and even to some extent, mosses and liverworts (Bryophytes*) and ferns and their allies (Pteridophytes). The association is generally mutual, but in some species (or in certain circumstances) mycorrhizae can cause infection in the host plant.

Many colourful fungi, such as the Fly agaric Amanita muscaria form ectomycorrhiza (external mycorrhiza) with tree roots.

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Why fungal mycelium is essential to healthy plant and tree growth

Slippery Jack Suillus luteus © Ita McCobb

The fungus’ “mycelium” – the unique microscopic network of fine white laments (called “hyphae”), through which the fungus obtains its nutrition – forms an outer sheath around the fine roots of its partner tree or plant, protecting its partner and at the same time enhancing its partner’s ability to absorb the extra nutrients it provides.

The relationship is of two-way benefit. In the relationship the fungus receives carbon from its partner plant (or tree) in exchange it supplies its partner tree or plant with phosphorus, nitrogen, potash, zinc and water through the tips of the mycorrhiza.

While the entire process is still not completely understood, it is believed that the fungus’ extremely fine and sprawling “mycelium” is better able to absorb these nutrients, especially from poor soils, than is its partner plant or tree.

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References: The British Mycological Society; OxfordEnglish Dictionary, Oxford University Press; Champignons, toxiques & comestibles, Institut Klorane; Collins Fungi Guide, Stefan Buczacki, Collins; Mushrooms, Roger Phillips, MacMillan.