“The view of plants as autonomous individuals with neat borders is causing destruction.”
If you put fresh, fine roots in a dish of water, you’ll see fine fungal filaments – or hyphae – stringing off them. If you boil roots, stain them
with a dye, and mount them on a slide, you’ll see fungi winding along and branching into delicate feathery lobes within plant cells. It’s difficult to imagine a more intimate set of poses. By means of this relationship, plants are able to obtain minerals foraged by the fungi in the labyrinthine rot-scapes of the soil. In return, plants supply fungi with energy rich carbon compounds – sugars or lipids – produced in photosynthesis.
Both plants and fungi use the other to extend their reach, and have done so for hundreds of millions of years: it was only by partnering with fungi that the algal ancestors of land plants were able to move onto the land. This makes mycorrhizal associations – from the Greek mykes, meaning fungus, and rhiza, meaning root – a more fundamental part of planthood than fruit, flowers, leaves, wood, or even roots. Today, more than ninety per cent of all plant species depend on mycorrhizal fungi, which lie at the base of the food chains that sustain much of life on Earth, including our own. The significance of this ancient alliance is difficult to overstate.
“Cultivate plants – in a plant pot, flower bed, garden or city park – and we cultivate fungal relationships.”
Fungi aren’t restricted to plant roots, however. All plants form relationships with fungi that live in their leaves and shoots, known as foliar endophytic fungi. These symbionts protect plants from pathogens and herbivores and increase their tolerance to a range of stresses, from heat to drought. If you harvest a grass from salty coastal soils and grow it without its fungal endophytes, it won’t be able to survive in its natural habitat. The same goes for grasses growing in hot geothermal soils. In a series of dramatic experiments, researchers swapped the fungal endophytes that lived in each type of grass so that coastal grasses were grown with hot geothermal fungi and vice versa. The proclivities of the grasses switched. Salt-loving grasses could no longer survive in coastal soils but thrived in hot geothermal soils. Hot geothermal grasses could no longer grow in the hot geothermal soils but thrived in the salty coastal soils.
Plant traits, in other words, may be more than ‘plant’ traits. In fact, what we call plants can be thought of as algae that have evolved to farm fungi, and fungi that have evolved to farm algae. Eat a plant, drink a wine, and we taste the outgrowth of fungal relationships. Cultivate plants – in a plant pot, flower bed, garden or city park – and we cultivate fungal relationships.
Still, the plot thickens. Fungi themselves depend on the bacteria and viruses that live within them: their microbiome. The presence or absence of a single virus can turn a fungus from a deadly pathogen of plants into a beneficial symbiotic partner. And bacteria that live within mycelial networks can enhance fungal growth, stimulate their metabolisms, produce key vitamins and even influence the relationships of mycorrhizal fungi with their plant partners. One species of mycorrhizal fungus, the thick-footed morel (Morchella crassipes), goes so far as to farm the bacteria that live within its networks: the fungus ‘plants’ bacterial populations, then cultivates, harvests and consumes them. There is a division of labour across the network, with some parts of the fungus responsible for food production and some for consumption.
“A large study published in 2018 suggested that the ‘alarming deterioration’ of the health of trees across Europe was caused by a disruption of their mycorrhizal relationships.”
Advances in the microbial sciences have deepened and expanded the notion of the individual and transformed swathes of biology – the study of living organisms – into ecology – the study of the relationships between living organisms. The implications are far-reaching. A large study published in 2018 suggested that the ‘alarming deterioration’ of the health of trees across Europe was caused by a disruption of their mycorrhizal relationships, brought about by nitrogen pollution. In viewing soils as more or less lifeless places, industrial agricultural practices have ravaged the underground communities that sustain us and all that we depend on. There are parallels with much of twentieth-century medical science, which considered ‘germ’ and ‘microbe’ to mean the same thing. Of course some soil organisms, like some microbes that live on your body, can cause disease. Most do quite the opposite. Disrupt the ecology of microbes that live in your gut, and your health will suffer – a growing number of human diseases are known to arise because of efforts to rid ourselves of ‘germs’. Disrupt the rich ecology of microbes that live in the soil – the guts of the planet – and the health of plants too will suffer.
Plants’ intimate relationships with their fungal associates evolved to deal with the challenges of a desolate and windswept world in the earliest days of life on land. Together, they evolved a form of agriculture, although it is not possible to say whether plants learned to farm fungi, or fungi learned to farm plants. Either way, we’re faced with the challenge of altering our behaviour so that plants and fungi might better cultivate one another.
It’s unlikely we’ll get far unless we question some of our categories and loosen the grip of some of our certainties about how we divide the world. The view of plants as autonomous individuals with neat borders is causing destruction. The word ecology has its roots in the Greek word oikos, meaning ‘house’, ‘household’,’ or ‘dwelling place’. Plant bodies, like those of all other organisms – including our own – are dwelling places. Can we think about a plant without also thinking about the mycorrhizal networks that lace outward from its roots into the soil? If we follow the tangled sprawl of mycelium that emanates from its roots, then where do we stop? Do we think about the bacteria that surf through the soil along the slimy film that coats roots and fungal hyphae? Do we think about the neighbouring fungal networks that fuse with those of our plant? And – perhaps most perplexing of all – do we think about the other plants whose roots share the very same fungal network?
Merlin Sheldrake is a biologist and author of Entangled Life: how fungi make our worlds, change our minds, sand shape our futures.