How they feed
Fungi are unseen feeders. By breaking down dead organic matter, fungi make it available to growing plants, thereby preventing its accumulation and adding to the overall health and efficiency of the planet.
The breakdown by fungi of litter, dead woody material and animal debris releases essential nutrients into the soil. This generally beneficial process can cause problems such as when dry rot attacks structural timbers. Fungi which act in this way are called saprotrophs or decomposers.
Fungi which kill some of their host’s cells, be they plant, animal or even fungus are called nectrotrophs. Generally their attack is not fatal. These include rust - and smut fungi, microscopic relatives of mushrooms and toadstools, which need a growing host as they attack new shoots - a life-style known as parasitic. Other fungi cause such extensive destruction that the host dies whereupon the fungus feeds on the corpse. Several larger mushrooms and toadstools fall into this category and are termed necrotrophs. Thankfully there are comparatively few fungi in Scotland which cause disease in man but some of these may prove fatal, especially in patients whose resistance to infection has been lowered in any way.
Over 80% of our trees, shrubs and wild flowers depend on fungi located either within or upon their roots. In both cases the hyphae scavenge nutrients from the surrounding soil, which in turn they make available to their host plant. In exchange the fungus receives simple organic nutrients and vitamins. In some cases these same hyphae assist the decomposition of litter. Such associations are called mycorrhizas (derived from Greek, meaning ‘fungus root’) and many of the mushrooms and toadstools we see in the autumn are involved in such processes. Different kinds of mycorrhizas occur in orchids, grasses and heathers. Many mycorrhizas are highly specific and will only be found with particular hosts. Loss of such hosts may therefore affect a whole range of fungi and any conservation management must take account of this.
Some fungi benefit directly from photosynthesis by forming close relationships with algae. This is such a close union that, as recently as the middle of the last century, they were considered to be a single organism in their own right and came to be known as lichens. Whilst the fungi obtain nutrients from the algae, the fungi protect the algae from drying out. This relationship and those in mycorrhizas are termed biotrophic.
Just as there are close relationships with plants, there are also close associations between fungi and invertebrate animals. In Scotland, some wood wasps and beetles use fungi to assist them in breaking down food for their larvae. In contrast oyster mushrooms capture eel-worms on special sticky knobs in the mycelium and use their body fluids as food.