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December 26, 2022 - January 29, 2023
This may sound like common sense, but from the standpoint of mechanistic medicine at the time it was a radical notion. The conventional approach was – and remains to a large degree – to use stuff, whether drugs or a surgical tool, to treat the stuff that the body is made out of, just as we might use tools to repair a machine. Drugs are normally understood to work through a pharmacological circuit that bypasses the conscious mind entirely: a drug affects a receptor, which triggers a change in symptoms. By contrast, psilocybin – like LSD and other psychedelics – appears to act on symptoms of
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One of our most robust mental models is that of the self. It is exactly this sense of self that psilocybin and other psychedelics seem to disrupt.
Terence McKenna was a great advocate of this view. Given a sufficiently large dose, he asserted, the mushroom could be expected to speak, plainly and clearly, talking ‘eloquently of itself in the cool night of the mind’.
Then what did psilocybin do for those fungi that evolved an ability to produce it? Why bother to make it in the first place? It’s a question that has been pored over for decades by mycologists and magic mushroom enthusiasts alike.
However, sometimes they don’t do much more than provide variations on a biochemical theme that might one day prove useful, or not.
The psilocybin gene cluster jumped between species of fungus that lived similar lifestyles in rotting wood and animal dung. These habitats are also the home of numerous insects that ‘eat or compete’ with fungi, all of whom should be sensitive to the potent neurological activity of psilocybin.
Could psilocybin be a deterrent produced by fungi to fuddle the wits of their insect pests? If so, it doesn’t seem
to be very effective.
He reported that consumption of these mushrooms resulted in ‘hilarity, incoherent talking, and … fantastic visions in brilliant colors’.
Most of the psychedelic research of the 1950s and 60s had taken place with LSD, or synthetic psilocybin in pill form, much of it produced by Hofmann in Switzerland.
It turns out that there are few environments where these mushrooms don’t grow, given sufficient rainfall.
For our altered states to count as an extended phenotype of the fungi the be-mushroomed human would need to serve the reproductive interests of the very fungi they had eaten.
Psilocybin-producing fungi don’t depend entirely on our altered states, as Ophiocordyceps depends entirely on the altered behaviour of ants. For tens of millions of years, they have grown and reproduced perfectly well without humans, and would probably continue to do so.
Theirs is a view shared by many traditional cultures that ritually use entheogenic plants or fungi. And it is a view commonly reported by contemporary users in non-traditional settings, many of whom report a thinning of the boundaries between ‘self’ and ‘other’, and an experience of ‘merging’ with other organisms.
Light was unfiltered by water, and carbon dioxide was more accessible – no small incentives for organisms that make a living by eating light and carbon dioxide.
These early alliances evolved into what we now call mycorrhizal relationships. Today, more than 90 per cent of all plant species depend on mycorrhizal fungi. They are the rule, not the exception:
For the relationship to thrive, both plant and fungus must make a good metabolic match. It is a familiar pact. In photosynthesis, plants harvest carbon from the atmosphere and forge the energy-rich carbon compounds – sugars and lipids – on which much of the rest of life depends.
It isn’t clear how mycorrhizal relationships first arose. Some venture that the earliest encounters were soggy, disorganised affairs: fungi seeking food and refuge within algae that washed up onto the muddy shores of lakes and rivers.
‘They have fungus-roots, myco-rhizas.’
Mycorrhizal fungi are so prolific that their mycelium makes up between a third and a half of the living mass of soils. The numbers are astronomical. Globally, the total length of mycorrhizal hyphae in the top ten centimetres of soil is around half the width of our galaxy (4.5 × 1017 kilometres versus 9.5 × 1017 kilometres).
If these hyphae were ironed into a flat sheet, their combined surface area would cover every inch of dry land on Earth two and a half times over.
Given that mycorrhizal fungi have been around for some 500 million years and aren’t restricted to the top ten centimetres of soil, these figures are certainly underestimates.
Mycorrhizal fungi unpack nutrients bound up in rock and decomposing material. These are fungi with a dual niche: part of their life happens within the plant, part in the soil.
What we call ‘plants’ are in fact fungi that have evolved to farm algae, and algae that have evolved to farm fungi.
Frank didn’t have much success in cultivating truffles, but in his enquiries he documented in vivid detail the entanglement between tree roots and the mycelium of truffle fungi.
Mycorrhizal mycelium behaved like a ‘wet nurse’, and enabled ‘the entire nourishment of the tree from the soil’.10
Metre-tall trees evolved into thirty-metre-tall trees in a few million years. Over this period, as plants boomed, the amount of carbon dioxide in the atmosphere dropped by 90 per cent, triggering a period of global cooling. Could plants and their fungal associates have played a part in this massive atmospheric transformation? A number of researchers, Field included, think it’s probable.
‘The levels of carbon dioxide in the atmosphere drop off dramatically at the same time as land plants are evolving increasingly complex structures,’
One of the biggest limits to plant growth is a scarcity of the nutrient phosphorus.
One of the things that mycorrhizal fungi do best – one of their most prominent metabolic ‘songs’ – is to mine phosphorus from the soil and transfer it to their plant partners.
Mycorrhizal fungi deploy acids and high pressure to burrow into solid rock. With their help, plants in the Devonian period were able to mine minerals like calcium and silica. Once unlocked, these minerals react with carbon dioxide, pulling it out of the atmosphere. The resulting compounds – carbonates and silicates – find their way into the oceans where they are used by marine organisms to make their shells. When the organisms die, the shells sink and pile up hundreds of metres thick on the ocean floor, which becomes an enormous burial ground for carbon. Add all of this up and climates start
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However, without taking account of mycorrhizal fungi, there is no way to make realistic estimates of how much phosphorus plants were able to access.
In a series of experiments, she had found that the outcome of mycorrhizal relationships varied depending on the climatic conditions in her growth chambers. Sometimes plants benefited more from the relationship, and sometimes less, a trait she terms ‘symbiotic efficiency’. If plants are hitched to an efficient mycorrhizal partner, they receive more phosphorus and grow more. Field was able to estimate how efficient mycorrhizal exchange would have been around 450 million years ago, when atmospheric carbon dioxide levels were several times higher than they are today.
he found that it was possible to change the entire global climate simply by turning the symbiotic efficiency up or down. The amount of carbon dioxide and oxygen in the atmosphere, and global temperatures – all varied according to the efficiency of mycorrhizal exchange.
‘Our results suggest that mycorrhizal relationships have played a role in the evolution of much of life on Earth.’
mycorrhizal fungi can provide up to 80 per cent of a plant’s nitrogen, and as much as 100 per cent of its phosphorus. Fungi supply other crucial nutrients to plants, such as zinc and copper. They also provide plants with water, and help them to survive drought as they’ve done since the earliest days of life on land. In return, plants allocate up to 30 per cent of the carbon they harvest to their mycorrhizal partners. Exactly what is taking place between a plant and a mycorrhizal fungus at any given moment depends on who’s involved. There are many ways to be a plant, and many ways to be a
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A plant’s fungal partners can have a noticeable impact on its growth – and its flesh. A number of years ago, at a conference on mycorrhizal relationships, I met a researcher who had been growing strawberry plants with different communities of mycorrhizal fungus. The experiment was simple.
If the same species of strawberry was grown with different species of fungus, would the flavour of the strawberries change?
He conducted blind taste tests and found that different fungal communities did seem to change the flavour of the fruit. Some had more flavour...
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Some fungi have been found to make tomatoes sweeter than others; some change the essential oil profile of fennel, coriander and mint; some increase the concentration of iron and carotenoids in lettuce leaves, the antioxidant activity in artichoke heads, or the concentrations of medicinal compounds in St John’s wort and echinacea.
‘How delicate is the mechanism by which the balance of power is maintained among members of the soil population,’
Anywhere from thousands to billions of root tips explore the soil, each able to form multiple connections to different fungal species.
In one set of experiments, she found that plant roots were able to supply carbon preferentially to fungal strains that provided them with more phosphorus.
By doing so, the fungus was able to transfer a greater proportion of its phosphorus to the plant at the more favourable ‘exchange rate’, thus receiving larger quantities of carbon in return.
Or does it always transport phosphorus within its network from areas of abundance to areas of scarcity, sometimes receiving a ‘pay-off’ from the plant, and sometimes not? We still don’t know.
Scaling up these findings to complex real-world ecosystems isn’t always possible. Much of the time we only see a small part of the picture. The result is that researchers know more about what mycorrhizal fungi are capable of doing than what they’re actually doing.
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Plants remain the easiest way in. It is through plants that the mycorrhizal extravaganza below ground most commonly erupts into everyday human life. The countless microscopic interactions that occur between fungi and roots express themselves in the forms, growth, tastes and smells of plants.
The last
What was it about these different species that determined their response to the changing climate?
