What we are seeing is just the fruiting body of the organism, (fungi are not plants, they have their own kingdom called … fungi). Most of the organism is under the ground, or under the bark, or below the surface of the leaf litter or the mulch, etc.
|Mycelium under some bark|
Below the surface, the fungus consists mostly of a root-like structure called the mycelium. The mycelium is the part of the fungus that 'consumes' the dead organic matter in the soil, giving fungi their title of decomposers or waste recyclers. Without fungi and other organisms performing this role, our world would be buried under dead leaves, logs, animal carcasses, faeces, etc.
|Trametes versicolour, a log decomposing fungus|
|Another log rotting fungus - Sterum ostrea (I think).|
In the process of consuming dead material, fungi release other nutrients for the plants to use. Some fungi have a mycorrhizal association with some plants. Without being too complicated, they exchange materials through their root systems.
|Diagrammatic representation of tree/fungi connections at the root zone.|
Many Australian plant species have complex and essential connections with fungi. Most of our orchids will not survive without a mycorrhizal association with a fungus. Many of our forest tree species need fungi to help them grow healthily, particularly during the first few years of growth.
|Healthy forest ecosystems need a healthy fungi population.|
|Spider Orchid on Mt Cannibal. All terrestrial orchids have a symbiotic relationship with fungi.|
Trees, indeed all plants, absorb carbon dioxide from the atmosphere. Research has now confirmed that most of the carbon is passed down to the root system of the tree where it is used by the fungi. When we declare that trees are carbon sinks, it really means that most of the tree's carbon is locked up by the fungi in the root zone.
Individual trees in an ecosystem can have their root systems linked by the mycelium network of fungi. It is now believed that this root network below the ground is the means of trees being able to 'communicate' with one another. Trees can secrete soluble chemicals into their roots where fungi can transport them to other nearby trees.
Of course, as far as trees are concerned, there are some bad or parasitic fungi but that might be a topic for a later conversation.