In the broadest sense, all fungi that colonize and break down wood ( xylobionts ) are called tree fungi . These mushrooms are scientifically referred to as lignicole mushrooms. This is a very large ecological group that includes species from different groups of fungi.
Hallimasch species, root sponges , fire crust fungus or lacquer spores, for example, are parasitic fungi that attack and decompose dead wood as well as living trees. When trees are felled, rootstocks should be cleared so that they do not serve as a breeding ground for fungi, if fungal infestation is to be avoided in the next generation of trees. Complete rootstock clearing can protect tree locations from fungal attack in the long term.
In the narrower sense, however, one speaks of tree fungi only when it is a question of species that colonize the trunks, stumps and branches of trees . In the following, a few essential differences between the tree-dwelling mushrooms or "higher mushrooms" are shown using the example of three selected mushrooms from the group of porlings .
Way of life of the tree fungi
Lignicole fungi live saproparasitic in both living and dead wood, commonly referred to as dead wood . They get their nutrients directly from the wood by breaking down usable substances using specific enzymes. A distinction is made between brown rot and white rot producing fungi. The brown rot breaks down all wood substances except lignin . White rot breaks down lignin, but is dependent on other energy-generating processes.
The former can only break down polysaccharides , including cellulose , and thus destroy the fiber structures in wood. The infected wood becomes brittle ( broken cubes ) and turns brown. About 80 percent of the wood can be used in this way, the lignin content remains unchanged. Another important change is the massive drying out of the wood. These brown rot fungi include, for example, the birch sponge ( Piptoporus betulinus ), the oak tangle ( Daedalea quercina ), the sulfur spore ( Laetiporus sulphureus ) as well as the red-rimmed tree sponge ( Fomitopsis pinyllicola ) and fence leafy ( Gloitopsis pinyllicola ), which are extremely common at least in Central Europe .
In addition to the polysaccharides, white rot fungi also decompose the lignin content of the wood. The sequence of dismantling can vary. The most common form, which also includes the breakdown of wood by the real tinder fungus ( Fomes fomentarius ), begins with a strong breakdown of lignin. The result is a white discoloration and fraying of the wood, which is due to the remaining polysaccharides, primarily cellulose. Due to the strong swelling capacity of the polysaccharides, the wood absorbs moisture and does not dry out. The degradation of the wood by white rot fungi can be almost 100 percent under optimal conditions.
Structure of the mushrooms
Settled wood is traversed by a network of hyphae , the foothills of which represent the actual places of wood decomposition and supply the fungus with nutrients. In order to reproduce, the mushrooms form fruiting bodies that house the actual spore carriers in the so-called hymenium. These fruiting bodies can take various forms, the most prominent being the consoles of the large Porling species.
In the case of the tinder fungus ( Fomes fomentarius ), the back of the console sits directly on the bark and evens out any unevenness. The base of the wood is a mycelium core , commonly known as the scale layer . However, this does not form a stem and is externally indistinguishable. The Sulfur Porling ( Laetiporus sulphureus ) also forms pedunculated consoles. Here, however, several consoles grow out of a large area of mycelium that attaches to the wood, each with its own hymenium . The mycelium of all consoles remains connected accordingly via an often quite massive, crust-like original mycelium. A third type of console is represented by the Birkenporling ( Piptoporus betulinus ). Here, as with the tinder fungus Fomes fomentarius , a mycelium core is also formed, from which the console with the hymenium grows. However, this remains the only point of attachment on the wood and forms an easily recognizable knot on the fruiting body. The console is stalked on one side.
Another important difference between the mushrooms concerns the mycelial structure of the fruiting body. This can be very different due to the different strengths of the connection between the hyphae and the structure of the cell wall and, above all, causes the different strength of the mycelial layers. The basic type is made up of thin-walled vegetative hyphae without significant chitinization of the cell walls , which can be linked to more strongly sclerotized skeletal hyphae and thick-walled connective hyphae. The tree fungus species in which this "trimitic" hyphae network is particularly dense and the fruiting body is therefore particularly hard include z. B. the tinder fungus ( Fomes fomentarius ). If the connective hyphae are missing and the trama consists only of skeletal hyphae and vegetative hyphae, one speaks of a dimitic network, as is found in the therefore much softer sulfur pore ( Laetiporus sulphureus ). The trama of particularly soft mushrooms, on the other hand, contains only vegetative hyphae and accordingly represents a monomitic mycelium.
Lifetime of mushrooms
Another essential distinction between the fruiting bodies concerns their “usage time”. As with the birch pore ( Piptoporus betulinus ) and the sulfur pore ( Laetiporus sulphureus ), this can last a single vegetation period. One speaks here of "annual" fruiting bodies - even if they often only remain alive and sporulate for less than a year. The fruiting bodies, especially in Piptoporus betulinus , can remain on the tree trunk as dead mycelium for a few years. In these annual species, new fruiting bodies sometimes break out of the infected wood year after year.
Perennial fruiting bodies are mostly found in the particularly hard tree fungi, to which, as already mentioned, the tinder fungus belongs. These “persistent” tree fungi also include the red-rimmed tree sponge already mentioned above (also known as “spruce sponge”, but it also infects living apple and cherry trees, for example) as well as many of our Phellinus species. In such forms with perennial fruiting bodies, a new growth zone and a completely new, but occasionally continuously fertile, hymenium form on the underside and front edge of the fruiting bodies. For this reason, one can often estimate the age of these fruit bodies by looking at them from the outside. However, several growth phases can occur within a year.
- Heinz Butin : Diseases of the forest and park trees. Diagnosis, biology, control. 2 spore boards. 3rd, revised and expanded edition. Thieme, Stuttgart and New York 1996, ISBN 3-13-639003-2 .
- Hermann Jahn : Mushrooms that grow on wood . Busse, Herford 1979, ISBN 3-87120-853-1 .