Being an Oak
by Jessica Moore, translated from Laurent Tillon
LECCINUM, THE BOLETUS, 1782
In which we discover that the soil holds a number of surprises for Quercus the oak, and that he will encounter organisms very different from himself: fungi. This encounter will be violent, and Quercus will be betrayed. But this symbiosis will provide him with new vital energy. He will subsequently gain access to an extraordinary world, consisting of exchanges that transcend the barriers between species.
The year is 1782.
Sitting at the foot of Quercus, I observe a dead oak in the clearing a little further along. A small bramble takes advantage of the opening and the light coming through the tree canopy. It sometimes produces a few berries that I like to pick. If the summer has had some rain, they are juicy. What a treat! While I graze on the fruit, I notice the stems of young oaks trying to reach through this impenetrable bush. Their destiny seems very precarious to me. But their challenges might also be a boon for other forest organisms. And perhaps they will get some help from another species, allowing them to eventually escape this thicket.
Given his environment and the history of this forest (we’ll come back to this), it’s likely that Quercus was subject to the same constraints at a very early age. Receiving help from others would have been vital for him.
Let’s go back to his first summer as a young sapling.
Quercus is floundering. He benefits from a few photons that penetrate the bramble, but he needs more space. The bramble is stifling his development. If this situation persists, he’ll end up withering in spite of all his efforts.
During this time, Leccinum spreads out and develops her network as much as possible. Because she’s infinitely tiny, she goes where she wants and reaches a multitude of mineral resources hidden in the ground, such as water, which can be rare.
Leccinum is a fungus, most recognisable to humans when she fruits. The orange oak bolete is a favourite of connoisseurs. But most of the time, Leccinum quercinum hides in the ground and stretches out each of her filaments as far as possible. Each year, in this way, she extends nearly thirty centimetres. This might seem ridiculously slow, but for an organism moving through the soil, and for whom the diameter of its tissues is around five to ten micrometres, this progress is a feat.
Leccinum sometimes fruits by making an epigeous mushroom; it emerges from the ground with a cap covered in thousands of spores, or tiny seeds, promising dispersal and perpetuation of the species.
But most of the time, Leccinum is invisible and leads a subterranean life. She is made up of hyphae, very fine filaments capable of stretching out into the volumes of earth and humus of the forest floor to compose a dense network called mycelium. This allows her to exploit large volumes of soil to reach basic nutrients such as nitrogen, potassium, phosphorus, magnesium, and other trace elements like copper and zinc. But gathering these chemical elements is one thing – preventing their recrystallisation while they’re being transported through the very-narrow hyphae is another. For this, she produces citrate or oxalate, organic acids that can break up complex molecules so they can pass through the tubes more easily.
The mycelium becomes an enormous circuit through which molecules circulate in all directions, without ever being stopped, except to create new hyphae. But, like all fungi, the bolete has one weakness: she can’t make the sugars, lipids, vitamins and complex molecules necessary for her development. She can survive for a long time on simplified molecules from the ground, but then she’s condemned to stagnate, and will never be able to fruit, reproduce, or scatter her spores to conquer new spaces. In order to flourish, she must find resources elsewhere. She must ask for help, and form alliances.
In her search for partners, long ago Leccinum found a tree. The connection of her hyphae with the roots of an oak allowed her to absorb these famous nutrients in exchange for water, trace elements and mineral salts. The pact benefits them both. But the oak has aged, and keeping all its eggs in one basket is too risky for our fungus. It’s in Leccinum’s nature to multiply her partners, without abandoning the already-established partnership. When you’re mycelium, you play every angle.
Leccinum is slowly expanding her network and continuing in her search when she detects some very particular structures emitting a signal that leaves no room for doubt. She has come across a very young oak who has just extended a brand-new root into the soil. If she heads directly for this root, the oak will probably react badly. He might not be able to prevent contact, but the connection would immediately be considered an act of aggression. To facilitate the encounter, Leccinum instead calls upon a bacteria, rhizobium, to mediate. When it extends into the soil, Quercus’s root emits molecules that can resemble hormones – flavonoids or betaines which, for example, help it to better resist stress related to heat or lack of water. Quercus produces them naturally to protect its root system. But this emission has an indirect effect: bacteria which also need water detect them, move toward them in the soil, and agglomerate to form nodules, like tiny little balls that make up the beginnings of the rhizobium, right before the apex of the emitting root. They are also naturally nitrogen-fixing, which the plant can benefit from.
These unique structures are mainly formed during the development of the root system of leguminous plants, such as peas; for oaks, there’s still some doubt about their existence, but it’s likely. So Quercus would benefit from these bacteria coming closer. The nodules they form aren’t part of our young oak, and demonstrate its capacity to accept partnerships with outside organisms from a very young age. So why not Leccinum? The latter perceives a chance to enter into contact with the growing tree, taking advantage of bacterial diplomacy.
Aside from soluble mineral ions and surface water, Quercus is unable to find all the nutrients necessary for his development. The tissues that form the extremity of his roots open to absorb the nitrogen agglomerated by the rhizobium bacteria. By opening in this way, the roots are prepared, in spite of themselves, for a new encounter. This is how Leccinum’s hypha enters the newly established relationship, when the bacteria detect the opportunity to reach the coveted water. Then, the door opens. The hypha goes straight to the heart of the root’s epidermic cells to begin the partnership, limiting the oak’s defensive responses; without this, the oak would feel attacked. Indeed, Quercus makes a simple acid, jasmonic acid, which helps warn neighbouring cells in case of attack. He uses it in his leaves just as much as in his roots. This acid is corrosive, thus to be avoided by intruders. But in reaction to these protective molecules, Leccinum makes neutralising proteins. The strategy works and Quercus is invaded in spite of his defences.
First he was betrayed by bacteria, now by his own organism. But strangely, this breach in the defenses of this young plant will cause an inverse effect when he’s grown: much later, the tree will react fiercely to each attack and make molecules that allow a more efficient immune response. And the invading fungi will aid this process: the mycelium will detect microbes in the soil that help improve the tree’s immune system in case of attack, provided the former transmits a molecule informing him of the problem. But for the moment, young Quercus does not know about the relationship that lies ahead. All it can tell is that the tips of its roots are under attack.
The hypha begins to insinuate itself between the root cells, breaking down their organisation to form a bond stronger than a marriage, called ectomycorrhiza. This is a perfect and inseparable welding of two very different organisms, the fungus and the growing sapling, which intertwines their cells to form an organ in its own right. Quercus ends up accepting the fungus inside his own tissues. The fungus doesn’t stop there. Now that the connection has been made and its acceptance forced, Leccinum produces auxin, a hormone usually synthesised by plants to solicit the production of new tissues. By tricking Quercus once again, Leccinum orders him to make new roots, into which she will promptly insert herself, multiplying the exchange gateways. This involuntary production of root tissues has an energy cost for Quercus – but one that will very quickly be compensated, as we’ll soon see. The two individuals are now intimately linked, until death do they part.
In this story, the rhizobium nodules played an essential diplomatic role for the future of the two protagonists. This is Quercus’s second experience of direct exchange with a species completely other from himself. This beneficial partnership has a name: symbiosis. In the symbiotic relationships it creates, Leccinum gathers sugars made by trees. Since the fungus pays in trace elements, which are the building blocks of these sugars, the relationship is largely agreed upon by the trees. These complex molecules are what allow them to grow. By entering into relationship with several trees, it’s possible that Leccinum creates an underground relationship between young Quercus and his older parent tree, which stands, after all, only a few metres away. And so, this connection can be seen in two ways: as a divergence of water, trace elements, and sugars destined for the older tree; or, as a conduit transporting help from the old tree to the new: a legacy, or even an inheritance.
The number of species of fungi in a given forest plot is considerable, but often difficult to catalogue exhaustively. Studies conducted that count the fructifications, or caps, of fungi on reference sites in several French forests still showed the emergence of new species, which had not been observed before thirty years after monitoring began. Although not all fungi bear fruit, or not each year, more than a hundred different species can be counted in a single hectare, whose hypha stretch out in all directions in the volume of soil just below the surface. Each mycelium is generally dependent on one tree, but some know how to adapt, and partner with forest species other than the one for which they are programmed. When a hypha binds to a tree, the tree may be connected on the other side of its root system to another mycelium, which is, in turn, linked to other trees. This creates a vast underground network in which molecules circulate and can move from one tree to another, forming a highly efficient system of communication and resource-sharing that benefits all the connected individuals, no matter what their species.
We often compare this network to the internet. The comparison falls short of being able to describe the totality of relationships and information that circulates via mycelia. Our internet functions for a single species, humans, and allows individuals to communicate and exchange extraordinary quantities of information. But there’s a great deal missing for it to be considered equivalent to the power of the mycorrhizal network. The latter goes much further, allowing for the exchange of not only information but vital nutrient molecules between individuals of different species. In theory, if they’re connected to the same network, trees as far apart as several hundred metres can communicate, and even help each other in the case of a food shortage.
As one of the new members of this vast network, Quercus is offered opportunities to develop and better resist the hazards he might encounter. This symbiotic relationship will be vital for him.
Quercus is still stuck in the bramble. But he has more than compensated for this handicap. With the help of Leccinum’s hypha, he now has access to an extensive, if somewhat anarchic, network. Leccinum is connected to many other roots of other individuals, mainly oaks. Some are young, like Quercus, but others, like Quercus’s parent tree, are mature. Up to thirty percent of the total amount of sugars made by trees return via sap to the mycelium. The mycelium is fed by it and sends the sugars throughout its network, to allow the furthest hypha to benefit and grow. However, if one of the trees is in trouble or weakened, it can conserve its resources at the expense of the fungus.
Another advantage has been observed for the trees: if one of them is attacked, it emits defence molecules and hormones, including some that circulate all the way to its roots. If the danger is sudden, the warning can even be issued via electrical impulses. This information is sent, along with carbon molecules, to the mycelium, which continues to redistribute it to the wider network. In this way, neighbouring trees are warned of potential danger. Quercus receives messages about the emergence of parasites or the dangers of various defoliators, and reacts by preparing for their potential arrival. He’ll be ready.
Quercus, an apparently solitary individual, has become an ultra-connected being, who seems to have access to everything this forest can offer. But while in Leccinum he has found an exceptional ally, other relationships are less happy. He becomes sensitive to the approaches of more threatening fungi, such as oidium, or powdery mildew, which is found on the surface and attacks leaves. Most worrying of all, he is still not able to photosynthesise enough sugars because of this cumbersome bramble. Fighting to reach a little bit of light from inside his prison, in order to make new tissues he must instead gather sugars through his roots. Could the bramble, which had been his saviour, turn out to be his gravedigger?
ABOUT THE CREATORs
Jessica Moore is an author and literary translator with a special interest in the shadowy corridors between languages, and between people. Her first book, Everything, now (Brick Books, 2012) is a love letter to the dead. The Whole Singing Ocean (Nightwood, 2020) is a true story blending long poem, investigation, sailor slang, and ecological grief. Her translations have been nominated for the International Man Booker, the French-American Foundation Translation Prize, and have won the UK’s Wellcome Prize and a PEN America Translation Award. Jessica lives in Tkaronto/Toronto, where she tends to her twins and her urban garden. Her work-in-progress, Porous, is a memoir of motherhood and art.
Laurent Tillon is a biologist and forestry engineer at the National Forestry Office in France. As a specialist in the ecology of bat colonies, he works on the functioning of ecosystems and the relationships between animal species and trees, with the aim of integrating biodiversity issues into forest management. He has been a volunteer conservationist for the Conservatoire d'espaces naturels du Centre Val-de-Loire since 2020, helping manage a bat habitat he discovered in his teenage years. He is also the author of Les Fantômes de la nuit, des chauves-souris et des hommes (2023). He lives in the Rambouillet forest, very near Quercus, his companion-tree.