Extreme networking
The largest living organism in the world is not a blue whale, an elephant or a sequoia tree, but a fungus. With its underground mycelium, a single honey fungus in Oregon’s Malheur National Forest covers an area of around nine square kilometres – and has been doing so for thousands of years. The giant fungus fascinates researchers beyond these superlatives with the way it exists and grows. A mycelium, the network of fungal threads, is always a highly functional, decentralised and adaptable system. However, a mycelium of this size opens up entirely new horizons for science.
Chance discovery of the largest living organism in the world
The discovery of the giant honey fungus was by chance. In the 1990s, forest scientists in the US State of Oregon noticed a mysterious tree dieback. A research team led by forest scientist Catherine Parks collected 112 samples of fungus-infested tree roots. The surprising finding after multiple genetic analyses was that the majority of samples were genetically identical and originated from a single organism of the species “Dark Honey Fungus” (Armillaria ostoyae) – a scientific sensation.
Long-lasting and highly interconnected
Subsequent research revealed further superlatives. The giant fungus has been spreading across this forest area since at least the 1900s – some even estimate it at over 8000 years – and now weighs at least 7500 tonnes, with estimates ranging up to 35,000 tonnes. Spanning nine square kilometres, its mycelium is now the same size as around 1200 football pitches. However, this gigantic phenomenon remains largely invisible to the human eye, because this mycelium, the actual body of the fungus, lies underground in the form of a widely branched, fine network of cell threads, known as hyphae.
The mycelium – a smart network without a control centre
Their mycelium is what makes fungi in general – and this giant honey fungus in particular – so unique. This underground fungal network forms a complex web that runs through the soil. Since these are cells of a single organism, the hyphae are all genetically identical and grow, similar to plant roots, through cell division. Fungi mycelia can therefore branch out for miles.
The network functions without a central control organ, such as the brain in animals, but is nevertheless highly organised, similar to the root system of plants. Fungi perceive chemical and physical stimuli such as temperature, humidity, chemical messengers from tree roots or even ground vibrations via their mycelium and react to them by, for example, adjusting their direction of growth. Just as there is now initial data on communication between plants, some researchers also suspect that there may be communication, perhaps chemical, between fungi.
Perfect growth conditions
The honey fungus and its various subspecies can be found all over the world. The largest known European fungus to date, also a honey fungus, lives in Switzerland and its mycelium covers a mere estimated 500 to 800 square metres.
The fact that an Armillaria fungus was able to grow to such an extraordinary size in Malheur National Forest can be explained, at least in part, by the special environmental conditions there. In the dry climate of Oregon, the honey fungus rarely forms fruiting bodies and therefore finds it hard to reproduce sexually. This certainly favoured its vegetative spread. Over thousands of years, the mycelium continued to grow undisturbed, supported by suitable host trees in an almost untouched forest area.
Ambivalent honey fungus
Although the Dark Honey Fungus with its dark brown cap-shaped fruiting bodies appears harmless, on closer inspection it turns out to be a parasite. Its mycelium network is intelligent for its own life and growth, but for its environment it’s potentially dangerous.
Honey fungi are continuously expanding their mycelial network through the forest soil, always looking for a new host in the form of the next tree. There, the fungus pushes mycelium cells upwards from the roots under the bark and extracts water and nutrients from the tree.
Healthy trees often manage to fend off Armillaria through wound tissue. This can lead to the development of a fairly stable “symbiont equilibrium”, in which the tree helps to nourish the fungus. We still don’t know what benefits this has for the tree. However, if the tree becomes exhausted, the fungus spreads further and further inside and literally “sucks the sap out of the tree” until it eventually dies.
The honey fungus then continues to work its way up inside the trunk and, in collaboration with the other fungi, insects and micro-organisms, slowly destroys the wood until the tree falls down. And even then, the fungus helps to transform the dead wood into plant nutrients and valuable humus through recycling. Armillaria thus plays an important role in the nutrient cycle of the forest.
A hidden network with potential for the future
The better we understand it, the clearer it becomes that fungi are anything but inconspicuous. From an evolutionary point of view, they are masters of survival.
In addition to sustainable approaches such as growing fungal mycelia in moulds to manufacture objects – already in use for bicycle helmets – further research also promises exciting findings: in fungi themselves and especially in an organism of the dimensions of the giant honey fungus.
How does information management and processing work in the gigantic mycelium network? How can an organism become so old? Is it still a single organism, or has it split into many clones, so that the organisational structure remains manageable? If this is the case, how does genetic regulation take place so that the clones remain genetically identical and differences do not result through mutations?
Whatever fungus research may reveal, there is one thing we can already learn from Armillaria – strong and meaningful networking significantly increases efficiency.
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Sources:
https://www.scinexx.de/news/biowissen/wie-intelligent-sind-pilze
https://zeitundwelt.de/gesellschaft/der-groesste-pilz-der-welt
https://www.srf.ch/sendungen/me-biodiversitaet/hallimasch-das-ist-das-groesste-lebewesen-der-welt