“Fungi are everywhere but they are easy to miss. They are inside you and around you. They sustain you and all that you depend on. As you read these words, fungi are changing the way that life happens, as they have done for more than a billion years. They are eating rock, making soil, digesting pollutants, nourishing and killing plants, surviving in space, inducing visions, producing food, making medicines, manipulating animal behaviour and influencing the composition of the Earth’s atmosphere. Fungi provide a key to understanding the planet on which we live, and the ways we think, feel and behave. Yet they live their lives largely hidden from view, and more than 90 per cent of their species remain undocumented. The more we learn about fungi, the less makes sense without them. “Fungi” make up one of life’s kingdoms – as broad and busy a category as ‘animals’ or ‘plants’. Microscopic yeasts are fungi, as are the sprawling networks of honey fungi, or Armillaria, which are among the largest organisms in the world. The current record holder, in Oregon, weighs hundreds of tonnes, spills across 10 square kilometres, and is somewhere between 2,000 and 8,000 years old. There are probably many larger, older specimens that remain undiscovered.

Many of the most dramatic events on Earth have been – and continue to be – a result of fungal activity. Plants only made it out of the water around 500 million years ago because of their collaboration with fungi, which served as their root systems for tens of million years until plants could evolve their own. Today, over 90 per cent of plants depend on mycorrhizal fungi from the Greek words for fungus (“mykes”) and root (“rhiza”) which can link trees in shared networks sometimes referred to as the ‘Wood Wide Web’.

To this day, new ecosystems on land are founded by fungi. When volcanic islands are made or glaciers retreat to reveal bare rock, lichens (pronounced LY-kens) – a union of fungi and algae or bacteria – are the first organisms to establish themselves, and to make the soil in which plants subsequently take root. In well-developed ecosystems soil would be rapidly sluiced off by rain were it not for the dense mesh of fungal tissue that holds it together. From deep sediments on the sea floor, to the surface of deserts, to frozen valleys in Antarctica, to our guts and orifices, there are few pockets of the globe where fungi can’t be found. Tens to hundreds of species can exist in the leaves and stems of a single plant. These fungi weave themselves through the gaps between plant cells in an intimate brocade and help to defend plants against disease. No plant grown under natural conditions has been found without these fungi; they are as much a part of planthood as leaves or roots.3 The ability of fungi to prosper in such a variety of habitats depends on their diverse metabolic abilities. Metabolism is the art of chemical transformation. Fungi are metabolic wizards and can explore, scavenge and salvage ingeniously, their abilities rivalled only by bacteria. Using cocktails of potent enzymes and acids, fungi can break down some of the most stubborn sub- stances on the planet, from lignin, wood’s toughest component, to rock, crude oil, polyurethane plastics and the explosive TNT. Few environments are too extreme. A species isolated from mining waste is one of the most radiation-resistant organisms ever discovered, and may help to clean up nuclear waste sites. The blasted nuclear reactor at Chernobyl is home to a large population of such fungi. A number of these radio-tolerant species even grow towards radioactive ‘hot’ particles, and appear to be able to harness radiation as a source of energy, as plants use the energy in sunlight.

Mushrooms dominate the popular fungal imagination, but just as the fruits of plants are one part of a much larger structure that includes branches and roots, so mushrooms are only the fruiting bodies of fungi, the place where spores are produced. Fungi use spores like plants use seeds: to disperse themselves. Mushrooms are a fungus’s way to entreat the more-than-fun- gal world, from wind to squirrel, to assist with the dispersal of spores, or prevent it from interfering with this process. They are the parts of fungi made visible, pungent, covetable, delicious, poisonous. However, mushrooms are only one approach among many: the overwhelming majority of fungal species release spores without producing mushrooms at all. We all live and breathe fungi, thanks to the prolific abilities of fungal fruiting bodies to disperse spores. Some species discharge spores explosively, which accelerate 10,000 times faster than a Space Shuttle directly after launch, reaching speeds of up to a hundred kilometres per hour – some of the quickest movements achieved by any living organism. Other species of fungi create their own microclimates: spores are carried upwards by a current of wind generated by mush- rooms as water evaporates from their gills. Fungi produce around fifty megatonnes of spores each year – equivalent to the weight of 500,000 blue whales – making them the largest source of living particles in the air. Spores are found in clouds and influence the weather by triggering the formation of the water droplets that form rain, and ice crystals that form snow, sleet and hail.

Some fungi, like the yeasts that ferment sugar into alcohol and cause bread to rise, consist of single cells that multiply by budding into two. However, most fungi form networks of many cells known as hyphae (pronounced HY-fee): fine tubular structures that branch, fuse and tangle into Mycelium.

Mycelium describes the most common of fungal habits, better thought of not as a thing, but as a process – an exploratory, irregular tendency. Water and nutrients flow through ecosystems within mycelial networks. The mycelium of some fungal species is electrically excitable and conducts waves of electrical activity along hyphae, analogous to the electrical impulses in animal nerve cells. Mycelium Hyphae make mycelium, but they also make more specialised structures. Fruiting bodies, such as mushrooms, arise from the felting together of hyphal strands. The best estimate suggests that there are between 2.2 and 3.8 million species of fungi in the world – six to ten times the estimated number of plant species – meaning that a mere 6 per cent of all fungal species have been described. We are only just beginning to understand the intricacies and sophistications of fungal lives.”

Entangled Life – Merlin Sheldrake

TRUFFLES

Truffles are spore-producing organs, similar to the seed-producing fruit of a plant. Spores evolved to allow fungi to disperse themselves, but underground their spores can’t be caught by the wind, and are invisible to the eyes of animals. Their solution is to smell. Forests are filled with smells, each a potential distraction to animals. Truffles must be pungent enough for their scent to penetrate the layers of soil and enter the air, distinctive enough for an animal to pay attention, and delicious enough for that animal to seek it out, dig it up and eat it. Every visual disadvantage that truffles face – being entombed in the soil, difficult to spot once unearthed, and visually unappealing once spotted they make up for with smell.

Once eaten, a truffle’s job is done: an animal has been lured into exploring the soil and recruited to carry the fungus’s spores off to a new place and deposit them in its faeces. A truffle’s allure is thus the outcome of hundreds of thousands of years of evolutionary entanglement with animal tastes. Natural selection will favour truffle fungi that match the preferences of their finest animal spore dispersers. .

Truffles had evolved to communicate to animals their readiness to be eaten. Humans and dogs had developed ways to communicate with one another about truffles’ chemical propositions. A truffle’s aroma is a complex trait, and seems to emerge out of the relationships the truffle maintains with its community of microbes, and the soil and climate it lives within – its terroir.

Truffle fruiting bodies house thriving communities of bacteria and yeasts between a million and a billion bacteria per gram of dry weight. Many members of truffles’ microbiomes are able to produce the distinctive volatile compounds that contribute to truffles’ aromas, and it is likely that the cocktail – of chemicals that reaches your nose is the work of more than a single organism. The smell of a truffle is made up of a flock of different molecules drifting in formation more than a hundred in white truffles, and around fifty in the other most popular species. These elaborate bouquets are energetically costly and are unlikely to have evolved unless they served some purpose. What’s more, animal tastes are diverse. Certainly, not all truffle species are attractive to humans and some are even mildly poisonous. Of the thousand-odd species of truffle in North America, only a handful are of culinary interest.

Truffles’ aromas are made in an active process by living, metabolising cells. A truffle’s odour increases as its spores develop, and its aroma ceases when its cells die. You can’t dry a truffle and expect to taste it later, as you can with some types of mushroom. They are chemically loquacious, vociferous even. Stop the metabolism, and you stop the smell. For this reason, in many restaurants, fresh truffles are grated onto your food before your eyes. Few other organisms are so good at persuading humans to disperse them with such urgency.

Allure underpins many types of fungal sex, including that of truffle fungi. Truffles themselves are the outcome of a sexual encounter: for a truffle fungus like Tuber melanosporum to fruit, the hyphae of one mycelial network must fuse with those of a separate, sexually compatible network, and pool genetic material. For most of their lives, as mycelial networks, truffle fungi live as separate mating types, whether ‘-‘ or ‘+’ – by fungal standards, their sexual lives are straightforward. Sex happens when a ‘hypha attracts and fuses with a ‘+’ hypha. One partner plays a paternal role, providing genetic material only. The other plays a maternal role, providing genetic material and growing the flesh that matures into truffles and spores. Truffles differ from humans in that either ‘+’ or ‘-‘ mating types can be maternal or paternal – it is as if all humans were both male and female and equally able to play the part of a mother or a father, provided we could have sex with a partner of the opposite mating type. How the sexual attraction between truffle fungi plays out remains unknown. Closely related fungi use pheromones to attract mates, and researchers have a strong suspicion that truffles, too, use a sex pheromone for this purpose.

Without homing, there could be no mycelium. Without mycelium, there could be no attraction between ‘-‘ and ‘+’ mating Without sexual attraction there could be no sex. And without sex, there could be no truffle.

However, the relationships between truffle fungi and their partner trees are just as important, and their chemical interactions must be intricately managed. The hyphae of young truffle fungi will soon die unless they find a plant to partner with. Plants must admit into their roots the fungal species that will form a mutually beneficial relationship, as opposed to the many that will cause disease. Both fungal hyphae and plant roots face the challenge of finding one another amid the chemical babble in the soil where countless other roots, fungi and microbes course and engage. It is another case of attraction and allure, of chemical call and response.

Both plant and fungus use volatile chemicals to make themselves attractive to one another, just as truffles make themselves attractive to animals in a forest. Receptive plant roots produce plumes of volatile compounds that drift through the soil and cause spores to sprout and hyphae to branch and grow faster. Fungi produce plant growth hormones that manipulate roots, causing them to proliferate into masses of feathery branches with a greater surface area, the chances of an encounter between root tips and fungal hyphae become more likely.