Without Fungi, How Can the Agricultural Ecology on Which Our Survival Depends Be Possible?
Foodthink Says
These life forms, distinct from both plants and animals, stand as mysterious, powerful presences too often ignored — offering guidance to humanity on its path towards coexisting with nature. How do fungi and plants flourish together in collaboration? What vital role do mycorrhizal fungi play in agricultural ecology, serving as the connective tissue between plants and soil? And under the relentless pursuit of ever-higher yields, how has the very foundation sustaining agricultural ecosystems been torn apart?
We present an excerpt from the new book Entangled Life. By understanding the deep interactions between fungi and plants beneath our feet, perhaps we can begin to imagine a different possibility: that the future of agriculture may lie not in ever more chemicals, but in rediscovering and nurturing the subtle, intricate symbiotic relationships within soil ecosystems. 🍄🟫
“Human health and wellbeing necessarily depend on the efficiency of these mycorrhizal associations.” So wrote Albert Howard, one of the founding voices of the modern organic farming movement and an ardent champion of mycorrhizal fungi. In the 1940s, Howard warned that the widespread use of chemical fertilisers would destroy mycorrhizal associations, yet “it is precisely the mycorrhizal networks that… bind the fertile soil and the trees it nourishes together so closely”. The damage wrought by chemical fertilisers reaches far. To sever these “living threads of fungi” is to undermine the health of the soil itself. Crop health and yields will suffer in turn — and so, too, will the animals and people who feed on them. “Can humanity regulate its own behaviour to preserve its most essential asset — the fertility of the soil?” Howard asked. “The future of human civilisation depends on the answer to this question.”
Howard’s tone was a touch hyperbolic, but in the eighty years that followed, the questions he raised have grown ever more urgent. By some estimates, modern agriculture has been remarkably efficient: crop yields doubled during the second half of the twentieth century. Yet the single-minded pursuit of yield alone has exacted a severe toll. Agricultural development has caused widespread environmental destruction and accounts for a quarter of global greenhouse gas emissions. Even with heavy pesticide use, between 20 and 40 per cent of crops are still lost to pests and disease each year. Although fertiliser use grew seven-hundredfold over the second half of the twentieth century, the growth in global agricultural output has plateaued. Every minute, an area of topsoil the size of thirty football pitches is lost to erosion worldwide. Meanwhile, humanity wastes a third of the food it produces, and demand for crops is set to double by 2050. The urgency of this crisis cannot be overstated.
Can mycorrhizal fungi offer part of the solution? It might seem a silly question. Mycorrhizal associations are as old as plants themselves, and for hundreds of millions of years they have been shaping the fate of the planet. Whether or not we think of them, mycorrhizal associations have always profoundly influenced crop harvests. For thousands of years, traditional farming in many parts of the world paid close attention to soil health, quietly sustaining the fungal relationships of plants. Yet throughout the twentieth century, our neglect of them has caught up with us. In 1940, Howard’s greatest fear was that advances in modern agriculture would come at the expense of “the life of the soil”. His fear has since become reality. Agricultural practice has treated soil as a near-lifeless void, and the underground communities that sustain edible life have been devastated as a result. There are many parallels with much of the medical science of the twentieth century, which conflated the “germ” with the “microbe”. To be sure, some organisms living in soil can cause disease, just as certain microbes in our bodies can; but the effects of the vast majority of microbes are quite the opposite. Disturb the microecology in which gut microbes live, and our health will suffer — many of the diseases afflicting humans today are linked to the over-eradication of “germs”. Soil is the gut of the Earth; disrupt the complex ecology of its microbes, and plant health will suffer.
In 2019, researchers at Agroscope, the Swiss agricultural research institute in Zurich, published a study measuring the scale of the damage by comparing the impact of organic and conventional “intensive” farming on the fungal communities around crop roots. By sequencing fungal DNA, the researchers were able to compile networks showing how fungal species connect to one another. They found “striking differences” between organically and conventionally managed fields. In organically managed fields, mycorrhizal fungi were not only more abundant but also formed more complex communities: the researchers identified 27 highly connected “keystone species”, whereas in conventionally managed fields, there were none. Many studies have reported similar findings. Under the combined pressures of tillage, chemical fertilisers and fungicides, intensive agriculture has drastically reduced the abundance of mycorrhizal fungi and altered their community structure. Whether organic or not, more sustainable farming practices typically allow soils to sustain more diverse mycorrhizal communities and richer fungal mycelium.
Do these differences matter? Much of agricultural history has been a history of ecological sacrifice. Forests have been felled to make way for cropland, and shrublands cleared to expand it. Why should the microbial communities in soil be any different? Surely, by fertilising our fields to “feed” our crops, we have replaced the mycorrhizal fungi? Having rendered fungi redundant, why should we care about them at all?
Mycorrhizal fungi do far more than merely nourish plants. Some researchers at Agroscope describe them as keystone species, while others prefer to call them “ecosystem engineers”. Mycorrhizal mycelium is living, adhesive stitching, weaving through the underground to hold soil and water in place; without fungi, both are easily lost. Mycorrhizal fungi increase the soil’s water-holding capacity and can reduce nutrient loss from rainfall by as much as half. A significant portion of the organic carbon in soil — which exceeds that in plants and the atmosphere combined by a staggering factor of two — is locked within the tough organic compounds produced by mycorrhizal fungi. Organic carbon channelled into the soil through mycorrhizal pathways supports complex food webs. In a single teaspoon of healthy soil, alongside hundreds or even thousands of metres of fungal mycelium, there are far more bacteria, protists, insects and other arthropods than the total number of humans who have ever lived.
There are now numerous projects aimed at providing fungal solutions to agricultural problems, and Katie Field is one of the researchers funded through such programmes. “The whole relationship is far more variable and more susceptible to environmental influence than we tend to assume,” she tells me. “Very often, fungi do not help crops absorb nutrients. The effects of mycorrhizal associations are highly unpredictable, depending entirely on the species of fungus and plant, and the environment in which they grow.” A number of studies have reported similar unpredictability. In the selective breeding of most modern crop varieties, the capacity to form efficient mycorrhizal associations has been overlooked. We have bred wheat that grows rapidly in conditions of abundant fertiliser, and ended up with plants that have been ‘spoilt’ — having almost entirely lost their ability to cooperate with fungi. Field observes: “It is something of a small miracle that there are still fungi colonising the roots of crops like these.”
The delicate nature of mycorrhizal associations lies in the fact that the most obvious intervention — supplementing plants with mycorrhizal fungi and other microbes — is a double-edged sword. Sometimes, as Samwise Gamgee the hobbit discovers in The Lord of the Rings, introducing soil microbial communities to plants can not only support the growth of crops and trees but also breathe new life into degraded soil. But whether such practices truly work depends on ecological fit. A poorly matched mycorrhizal fungus may do more harm than good to a plant; worse still, introducing opportunistic fungi into a new environment may allow them to displace native fungal species, causing unforeseen ecological consequences. The fast-growing commercial mycorrhizal fungi industry often overlooks this fact, marketing commercial mycorrhizal fungi as a universally effective solution. Much like the booming human probiotics market, many strains are brought to the shelf not because they are particularly well suited to the task, but because they are easy to produce on an industrial scale. Even with sound guidance, applying a fungal inoculant to the environment is no panacea. Like all living organisms, mycorrhizal fungi thrive only under particular conditions. The microbial communities in soil are in a state of continuous assembly; if disturbance persists, the connections between them will not endure. For microbial interventions to take effect, agricultural practice must undergo deeper change — just as we make changes to our diet or lifestyle when we try to restore the health of a damaged gut microbiota.
Other researchers approach the question from a different angle. If humanity has inadvertently bred crops that form dysfunctional symbiotic relationships with fungi, surely it is also possible to turn the logic around and breed crops that can recruit efficient symbiotic partners. Field is already exploring this approach, aiming to select crop varieties with stronger symbiotic cooperation — “a new generation of super-crops capable of forming astonishing associations with fungi.” Kiers is equally intrigued by these possibilities, but she looks at the problem from the fungus’s perspective. Rather than breeding plants more likely to enter into symbiosis, she is cultivating fungi that are more beneficial to crops: strains that hoard fewer nutrients for themselves and, if possible, prioritise the plant’s needs instead.
In 1940, Howard lamented our lack of a “complete scientific explanation” for mycorrhizal associations. Our scientific understanding remains far from complete, but as the environmental crisis intensifies, expectations are growing that the introduction of mycorrhizal fungi could transform the trajectory of agriculture and forestry, and help restore impoverished ecosystems. In the early days of terrestrial life, mycorrhizal associations evolved in response to the survival challenges posed by barren landscapes and harsh weather conditions. Plants and fungi jointly evolved a form of agriculture — though we do not know whether the plants learned to farm the fungi or the fungi learned to farm the plants. In either case, we face the challenge of changing our own behaviour so that plants and fungi may cultivate each other more effectively.
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— From the Prologue to Entangled Life
Author: Merlin Sheldrake (UK)
Translator: Luo Dinghao Editor: Zhou Songyan
ISBN: 978-7-5596-7775-4
Beijing United Publishing Co., October 2024, 1st Edition