Fungi and the Environment

Saprotrophic

Saprotrophic fungi obtain their nutrients from dead organic matter. There are many forms of dead organic matter—leaf litter, dung, soil, dead animals, wood and dead fungi-to name just a few. Saprotrophic fungi use them all. Saprotrophic fungi feed on and recycle about 85% of the carbon from dead organic matter, with bacteria and animals responsible for the other 15%. These fungi release the locked-up nutrients that can then be used by other living organisms, making the fungi vital to the health of terrestrial and aquatic ecosystems around the world.

Mycena clarkeana and Hericium clathroides break down complex organic molecules in wood and feed on the resulting, simpler products. Another wood decay fungus is Gloeophyllum separium, which grows only on the dead wood of conifers—both introduced conifers such as pine and native conifers such as Callitris.

Aleuria aurantia, Aseroë rubra and Hygrocybe lanecovensis feed on organic matter in soil.

Piptoporus australiensis grows on dead wood, often on wood that has been charred in a fire.

Morchella elata is saprotrophic or possibly weakly mycorrhizal and fire often triggers the production of abundant fruiting bodies.

You'll find Crucibulum laeve on a variety of dead materials—even herbivore dung. Pilobolus is a genus of saprotrophic fungi that are specialist dung inhabiters. You'll find them on the dung of many species of herbivorous animals. They are often the first species to appear on fairly fresh dung.

Parasitic

A parasite obtains its nutrients from another living organism, with no benefit to the other organism. Some parasitic species do not kill the organisms they feed on. There are parasites with very specific host requirements and may only attack a single species, whereas others may parasitize hosts from a variety of genera.

Cordyceps gunnii parasitizes the larvae of Ghost Moths in the genus Oxycanus. By the time the fruiting body appears the larva (out of sight, underground) has been killed by the mycelium of the fungus.

For some years many areas of the world have been seeing a decline in frog numbers and research has shown that a chytrid, Batrachochytrium dendrobatidis, is a major culprit. However, the ecologies of these chytrid species are still not understood.

Mutualistic

A mutualistic fungus associates with another organism, usually with some benefits to both partners but always with benefits to the other organism. In a mutualistic associations, the benefits need not be equally shared. You will often see the word symbiotic used to describe associations between different organisms and that word literally means 'living together'. It's a general term covering all types of associations, with no implication about the nature of the association. Hence, parasitic and mutualistic are two examples of symbiotic associations. The photo shows Phlepobus marginatus a very large mycorrhizal fungus.

A very important form of mutualistic association is a mycorrhiza. The word mycorrhiza is derived from the Classical Greek words for 'mushroom' and 'root'. In a mycorrhizal association the fungal hyphae of an underground mycelium are in contact with plant roots, but without the fungus parasitizing the plant. In fact the association is commonly (but by no means always) mutually beneficial. Through photosynthesis a chlorophyll-containing plant makes simple carbohydrates (using carbon dioxide, water and sunlight). About 90% of plant species form mycorrhizae and in many of these associations between 15% and 30% of the food produced by the plant moves through to the fungi. The associated fungal mycelia are adept at extracting minerals, especially nitrogen and phosphorus from the soil and these pass through to the plants. Mycorrhizal fungi can also protect plants against pathogenic fungi and micro-organisms. All in all, mycorrhizal fungi are very important for plant health, especially in Australia's nutrient-poor soils, where these partnerships are often essential to a plant's survival.

Mycorrhizae are formed by fungi in the Divisions Zygomycota, Ascomycota and Basidiomycota.

The picture shows pots of leeks (Allium porrum). The pots in the top row have been grown with an associated mycorrhizal partner Glomus mosseae whereas the pots in the bottom row have been grown without a mycorrhizal fungus.

You will find mycorrhizal associations from well-watered forests to the arid areas. The eucalypts, almost synonymous with Australia, are mycorrhizal, as are other genera in the same family (the Myrtaceae)—for example, Kunzea, Leptospermum and Melaleuca. Outside the Myrtaceae the genera Acacia, Casuarina and Nothofagus are further examples of common mycorrhizal genera found in the Australian bush. So, whenever you're looking at a gum tree, a tea-tree, a she-oak or a wattle-think about the fungal partners in the soil. Many of the imported garden trees in Australia are also mycorrhizal, for example beeches, oaks, firs and pines. Numerous crop plants form mycorrhizae and an example of this is the grass family, which gives us many of our staple cereals.

The picture shows an arbuscle of Glomus mosseae in a root cell of a leek (Allium porrum). The narrow filaments, stained darker blue, are fungal hyphae. Near the centre of the photo you can see a very short offshoot from one hypha and the densely bushed arbuscle growing in one of the rectangular root cells.

The species in the genus Zelleromyces are further examples of mycorrhizal fungi. These are examples of the native 'truffle-like' fungi which are sought out as food by various native animals, such as the Long-Footed Potoroo. While the Zelleromyces that is pictured is a native species there are also some introduced 'truffle-like' fungi in Australia. An example of this is Rhizopogon luteolus which grows in association with introduced pine trees.

The species in the genus Pisolithus are mycorrhizal and are often found in forest clearings or pushing up through bitumen road edges, near eucalypts.