Collins Mushroom Miscellany. Patrick Harding
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Название: Collins Mushroom Miscellany
Автор: Patrick Harding
Издательство: HarperCollins
Жанр: Природа и животные
isbn: 9780007596683
isbn:
A small number of toadstools obtain their food by growing on, or in close proximity with, the fruitbodies of other fungi. Parasitic bolete (Pseudoboletus parasiticus) is a small yellow-brown-capped bolete that is occasionally found growing from the base of fruitbodies of common earthball (Scleroderma citrinum). As its name implies, it has long been presumed to be parasitic on the earthball, but some researchers believe that it only requires the presence of the earthball to stimulate fruiting and is not a parasite. Similar doubts surround the rare piggyback rosegill (Volvariella surrecta), which I have only seen once in the past 30 years when I found clusters of the toadstool emerging from the decaying remains of some clouded agarics (Clitocybe nebularis). The rosegill could be a parasite or live only on the dead fruitbodies of clouded agaric; it has never been found in any other situation. The well-known yellow brain (Tremella mesenterica), a jelly fungus that brightens old stems of gorse and other shrubs through the winter, has now been found to be parasitic on the mycelium of another fungus within the twig. Life is not always what it seems.
Microfungi occupy many more habitats than do the larger mushrooms and toadstools. These include both fresh and salt water. British examples of the former that have come to public attention are fish moulds, one of which causes black patches and the untimely death of many a pet goldfish, and another which results in the death of salmon. Fungi also attack insects, including house flies, and the honeycomb of hive bees. Plant parasites include the rust fungi which, along with mildews and related ‘moulds’, cause immense damage in both horticulture and agriculture. Microfungi cause food spoilage and also kill trees, although the fungus that has left its mark by killing elm trees is in fact an ascomycete, but with tiny fruitbodies that are rarely seen (see here).
Bread mould–Rhizopus stolonifera, scanning electron micrograph of a sporangium
{Jeremy Burgess/NHPA}
Humans provide an unwelcome home for fungi in the form of ringworm and thrush. Some fungi have even caused eye infections in contact lens solutions. Species of Malassezia, tiny yeast-like fungi, are present on our skin where they feed on the oily products of our sebaceous glands. These fungi can cause dermatitis and more commonly the shedding of skin flakes; so even dandruff can be blamed on fungi. Other microfungi result in the brown foxing seen in old books, the etching of the glass in cameras and field glasses, and the spoiling of the surface of CDs.
Perhaps most intriguing of all is the fungus that ‘eats’ jet and diesel fuel. Oil is, of course, an organic material, being composed of the long-dead remains of marine organisms, so it should come as no surprise that a range of microfungi has been detected in oil-based fuels. The most important of these is the creosote fungus Amorphotheca resinae, which not only breaks down creosote (which has been used as a preservative against fungi) but can also feed on jet fuel (kerosene) as long as at least a little water (ten parts of water per million of fuel is enough) is available. Empty tanks are vulnerable to condensation in humid conditions and this can provide the necessary water. High-flying aircraft experience very low temperatures, but the creosote fungus can put up with temperatures down to –25°C. The greatest danger to planes and their passengers comes from the fungal mycelium, which may block filters and small pipes, thus preventing fuel flow to an engine.
As with all fungi, preventing the initial infection is one way of limiting damage. Many years ago I was told a story by someone who had worked for the RAF. He recounted a big NATO exercise involving jet planes from different countries which, as part of the training, were refuelled in mid-air from special tanker planes. Only later was it discovered that one tanker plane was infected with creosote fungus and, in a manner analogous to the transmission of sexual disease, the fungus had been passed on in the refuelling process. Expensive decontamination was required. The same fungus can also live on diesel (contaminated with water), resulting in fuel blockage in cars and lorries. Fungi really are ‘Here, there and everywhere’.
Getting to the Root of the Matter
Close up of fly agaric – Amanita muscaria, a common mycorrhizal fungus
As an undergraduate, over 40 years ago, I learnt about the way in which plants absorb water and nutrients through their roots. Descriptions of the chemical and physical processes involved were accompanied by pictures of root hairs and estimates of their phenomenal surface area. No mention was made of fungi. In separate lectures I learnt that some species of mushroom and toadstool formed intimate relationships with the roots of trees.
Some of the earliest work on the link between trees and fungi was initiated in the 1880s. It followed a request by the Prussian Minister for Agriculture, Lands and Forests for research into the commercial growing of truffles. A.B. Frank examined tree rootlets and observed their associated sheath of fungal threads. He called the association a mycorrhiza [from the Greek mykes, (Latin mycos) fungus, and rhiza, root].
A mycorrhiza is now defined as a symbiotic relationship (in that usually both plant and fungus benefit) in which the mycelium of a fungus supplies soil-derived nutrients to a plant root. In return the fungus is supplied with sugars manufactured by the plant. About 40% of the world’s woodland mushrooms and toadstools are believed to be involved in mycorrhizal relationships with trees. However, trees are not the only plants involved and recent research has estimated that over 90% of plant species in the world develop fungus roots through which nutrients and water are absorbed.
Given the Greek/Latin basis of the word mycorrhiza, the plural was originally written as mycorrhizae; a term I remember using in my student days. In the modern world it appears that mycorrhizae have been replaced by mycorrhizas, a reversal of the Victorian pedantry that fought against funguses in favour of fungi as the plural of fungus. More confusing still is the use of mycorrhiza to imply the plural; a cause of sleep loss only alleviated by the counting of sheeps.
Only 3% of the world’s plant species produce sheathing mycorrhizas of the type first studied in the 19th century and now termed ectomycorrhizas (Greek ektos, outside). Among these plants are many common trees (and some woody shrubs) of temperate regions, while the fungal partners include well-known mushrooms and toadstools. Ectomycorrhizas are commonly associated with trees such as oak, beech, birch, willow, alder and hazel, together with conifers including pine, larch and spruce. Tree species rarely, or never, forming ectomycorrhizas include sycamore, ash, elm, rowan and hawthorn; a major reason why the ground under these trees is less productive for mushroom hunters.
Fungi that form ectomycorrhizas with only one, or a small number of tree species include edible species of truffle, chanterelle, bolete, milkcap and hedgehog mushroom along with toadstools such as death cap (Amanita phalloides), fly agaric (Amanita muscaria) and brown rollrim (Paxillus involutus). A tree’s roots may cover an area that is much greater than its canopy and this can result in the production of fruitbodies of ectomycorrhizal fungi as far as 100m from their host’s trunk; the connection is not always obvious. Confusingly, the hyphae of some ectomycorrhizal fungi obtain their nutrients from fallen leaf litter rather than via plant roots. Woodland toadstools occurring on areas of chalk grassland where there are no trees have been shown to form mycorrhizas with rock-roses, which are small woody shrubs. While leading a group of botanists to see the marsh helleborine orchid in the wet dune slacks near Harlech I was fascinated to observe several large fruitbodies of brown rollrim (Paxillus involutus) СКАЧАТЬ