Beneath our feet _ by George Monbiot

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Beneath our feet is a miracle. It’s a thin cushion between rock and air, on which our lives depend. Few of us think about it. Few of us know anything about it. Try asking someone – anyone – what soil is. I’ve done it a few times, and the results made my head spin. Some people say it’s ground-up rock. That might be true of regolith on the surface of Mars, but not of soil on planet Earth. Others that it’s a mixture of everything that falls to the ground. But the most depressing answer I’ve received is: «It’s just dirt». Dirt is what soil is called in the US, and like dirt is how we treat it.

So what is soil? The astonishing truth is that no one really knows. We know that it’s an ecosystem: one of the most diverse and abundant ecosystems on earth. Soil in mid-latitudes can be as diverse as the Amazon rainforest, and as little studied. Beneath one square metre of land, in the right conditions, there may be several hundred thousand tiny animals, ranging across thousands of species. Scientists estimate that only 10% of them have so far been identified[1]. Wherever you go, you are walking over undiscovered species.

We also know that, like a coral reef, it’s a biological structure, built by the creatures that inhabit it. Without them, it would not exist. At the smallest scale, microbes create clusters of tiny particles stuck together with glue made largely from carbon. In fact, much of the organic carbon in the soil is used for this purpose, which is why soil collapses when the carbon content falls too far. Out of the tiny s tructures built by microbes, little scuttling animals like mites and springtails build bigger clusters. Out of these bigger clusters, the giants of the soil – such as ants and earthworms – create still bigger ones. Soil is fractally scaled. This means it’s organised on the same basic pattern, regardless of magnification: structures, within structures, within structures. This helps to explain its astonishing resilience in the face of droughts and floods: if it were just dirt, it would immediately be swept off the land.

In other words, soil is like a wasps’ nest or a beaver dam: a system built by living creatures to secure their survival. But unlike those simpler structures, it becomes an immeasurably intricate, endlessly ramifying catacomb, created by bacteria, plants and soil animals, working unconsciously together. Soil behaves like dust in a Philip Pullman novel: it organises itself spontaneously into coherent worlds.

Our ability to feed ourselves is an emergent property of these relationships. In fact, our lives depend on a feature that scarcely anyone has heard about: plants can talk. They speak in a remarkably sophisticated, precise and nuanced chemical language. And they invest vast resources into managing their relationships with the other living beings with which they talk. Of all the sugars that plants make through photosynthesis, they pump between 11% and 40%[2] into the soil. Before releasing them, they turn some of these sugars into compounds of tremendous complexity. These complex chemicals are not dumped randomly in the soil, but into the narrow band of soil immediately surrounding the root hairs, a zone we call the rhizosphere. They are released to create and develop the plant’s connections with microbes, especially bacteria. Plants produce such complex chemicals because they want to talk not to bacteria in general, but to the particular species that are most effective[3] in promoting their growth.

Soil is crammed with bacteria. Its earthy scent is the smell of the chemicals they produce. Petrichor, the smell released by dry ground when it is first touched by rain, is caused in large part by an order of bacteria called the actinomycetes. The reason that no two soils smell the same is that no two soils have the same bacterial community. Each, so to speak, has its own terroir. Biologists call soil microbes eye of the needle, through which the nutrients in decomposing materials must pass, before they can be recycled by the rest of the food web. They live throughout the soil, but in most corners, most of the time, they exist in limbo, waiting for the messages that will wake them up. When a plant root pushes into a lump of soil and pumps out signalling chemicals and sugars, it triggers an explosion of activity. The bacteria responding to its call consume the rich soup the plant feeds them on and proliferate at astonishing speed, to form some of the densest microbial communities on earth. There can be a billion bacteria[4] in a single gram of soil in the rhizosphere. The bacteria in the rhizosphere gather and unlock many of the nutrients on which plants survive. They produce growth hormones and other complex chemicals that help plants develop. When plants are starved of certain nutrients, or the soil is too dry or too salty, they will call out to the specific bacteria that can help to overcome these constraints. The microbes favoured by the plant create a defensive ring around the root, fighting off pathogens. They educate and stimulate the plant’s immune system, helping it to withstand attacks by fungi or insects.

When you take a step back from these facts, you see something remarkable. The rhizosphere lies outside the plant, but it is as essential to its health and survival as the plant’s own tissues. It is the plant’s external gut[5]. The parallels between the rhizosphere and the human gut are uncanny. For example, there are over a thousand phyla (= major groups) of bacteria. But the same four phyla[6] dominate both the rhizosphere and the guts of mammals.

This much we know, but with every year soil scientists make remarkable discoveries that force us to revise our understanding. Soil has properties that are shared with no other ecosystems and no other s tructures. Some of these properties, especially its coordinated response[7] to environmental stress, suggest that we might in time come to see it as a kind of super-organism. Little on earth is as dark to us as soil.

Upon this scarcely-understood system, we rely for 99% of our calories[8]. Yet we treat it with indifference, even contempt. Soil science is shockingly underfunded. There is no soil ecology institute anywhere on earth. While there are international treaties on telecommunication, civil aviation, investment guarantees, intellectual property, psychotropic substances and doping in sport, there is no global treaty on soil. We behave as if this amazingly intricate biological structure can withstand all we throw at it and continue to feed us. It can’t.

There are many ways in which we trash it. There’s the physical damage caused by careless ploughing. There’s contamination and urban sprawl. There is the growing of crops – especially maize and potatoes – in ways that leave the soil broken and exposed to winter weather. There’s the overuse of fertilisers: too much nitrogen prompts microbes to burn through the carbon that glues the soil structure together. There are the pesticides that kill soil animals as surely as they damage ecosystems above ground.

On farmland almost everywhere, soil is degrading at astonishing speed. But the impacts tend to be greatest where they hurt the most – in the poorest countries. This is partly because many of them are in the hotter regions of the world, where extreme rainfall, cyclones and hurricanes can rip exposed earth from the land, and partly because hungry people are often driven to cultivate steep slopes and other fragile places. One paper finds that erosion rates in the world’s poorest nations have risen by 12% in just eleven years[9]. In some countries, mostly in Central America, tropical Africa and South East Asia, over 70% of the arable land is now suffering severe erosion[10]. Climate breakdown, causing more intense droughts and storms of wind and rain, will exacerbate this loss[11]. Already, as a result of drought, soil erosion and the overuse of land, desertification affects one third of the world’s people[12]. Soil damage in dry places is one of the reasons why grain yields in sub-Saharan Africa have mostly failed to increase since 1960, even as they have boomed in the rest of the world.

We are weakening the soil’s capacity to renew itself, undermining its structure and making it more vulnerable to external shocks. The loss of a soil’s resilience might happen incrementally and subtly. As with other complex systems, we might scarcely detect the flickering until a shock pushes it past its tipping point. When severe drought strikes, the erosion rate of fragile and degraded soil can rise 6000 fold[13]. In other words, the soil collapses. Fertile lands turn, almost overnight, to dustbowls.

Our survival during the past hundred years has relied to a large extent on understanding and enhancing soil chemistry. Chemical manipulation has delivered extraordinary advances in crop production, but at a terrible cost to our long-term resilience. Feeding the world in the decades and centuries to come will depend on a much better understanding of soil biology. It will depend on a recognition that our survival is intimately connected with that of the creatures which build and sustain this scarcely known ecosystem. We do not care about what we do not know. The gaps in our understanding of the world beneath our feet are so wide that humanity could fall through them.

 

 

 

 

George Monbiot (London, b. 1963) is an author, Guardian columnist, and environmental campaigner. His best-selling books include Heat: How to Stop the Planet Burning (2006) and Feral: Rewilding the Land, Sea and Human Life (2013). His latest book is Regenesis: Feeding the World Without Devouring the Planet (2022). In 1995, Nelson Mandela presented him with a UN Global 500 Award for outstanding environmental achievement. In 2022, Monbiot was awarded The Orwell Prize for Journalism. Monbiot cowrote the concept album Breaking the Spell of Loneliness (2016) with the musician Ewan McLennan, and has made a number of viral videos. One of them, How Wolves Change Rivers, adapted from his 2013 TED Talk, has been viewed on YouTube more than forty million times; another one on natural climate solutions (#naturenow, 2019), in which he co-stars with Greta Thunberg, has been watched more than sixty million times.

 

 

 

 

 

 

 

 

 

 

references

1 David C. Coleman, Mac A. Callaham Jr., D. A. Crossley Jr., Fundamentals of Soil Ecology – 3rd edition, ed. Academic

Press, 2018

2 Hongwei Liu, Laura E. Brettell, Zhiguang �iu, Brajesh K. Singh, Microbiome-Mediated Stress Resistance in Plants, in:

Trends in Plant Science – vol. 25, issue 8, August 2020

3 Ioannis A. Stringlis, Ke Yu, Kirstin Feussner, Ronnie de Jonge, Sietske Van Bentum, Marcel C. Van Verk, Roeland L.

Berendsen, Peter A. H. M. Bakker, Ivo Feussner, Corné M. J. Pieterse, MYB72-dependent coumarin exudation shapes root

microbiome assembly to promote plant health, in: PNAS – Proceedings of the National Academy of Sciences of the United

States of America – vol. 115, issue 22, April 2018

4 Dilfuza Egamberdieva, Faina Kamilova, Shamil Validov, Laziza Gafurova, Zulfiya Kucharova, Ben Lugtenberg, High

incidence of plant growth-stimulating bacteria associated with the rhizosphere of wheat grown on salinated soil in

Uzbekistan, in: Environmental Microbiology – vol. 10, issue 01, January 2008

5 Shamayim T. Ramírez-Puebla, Luis E. Servín-Garcidueñas, Berenice Jiménez-Marín, Luis M. Bolaños, Mónica

Rosenblueth, Julio Martínez, Marco Antonio Rogel, Ernesto Ormeño-Orrillo, Esperanza Martínez-Romero, Gut and Root

Microbiota Commonalities, in: Applied and Environmental Microbiology – vol. 79, No. 01, December 2013

6 Rodrigo Mendes, Jos M Raaijmakers, Cross-kingdom similarities in microbiome functions, in: The ISME Journal –

Multidisciplinary Journal of Microbial Ecology – vol. 9, February 2015

7 Andrew L. Neal, Aurélie Bacq-Labreuil, Xiaoxian Zhang, Ian M. Clark, Kevin Coleman, Sacha J. Mooney, Karl Ritz, John

1. Crawford, Soil as an extended composite phenotype of the microbial metagenome, in: Scientific Reports – vol. 10, June

2020

8 Max Roser, Hannah Ritchie, Pablo Rosado, Food Supply, data source: UN Food and Agriculture Organization (FAO) –

available online @ www.ourworldindata.org/food-supply

9 Pasquale Borrelli, David A. Robinson, Larissa R. Fleischer, Emanuele Lugato, Cristiano Ballabio, Christine

Alewell, Katrin Meusburger, Sirio Modugno, Brigitta Schütt, Vito Ferro, Vincenzo Bagarello, Kristof Van Oost, Luca

Montanarella, Panos Panagos, An assessment of the global impact of 21st century land use change on soil erosion, in:

Nature Communications – vol. 08, December 2017

10 Martina Sartori, George Philippidis, Emanuele Ferrari, Pasquale Borrelli, Emanuele Lugato, Luca Montanarella,

Panos Panagos, A linkage between the biophysical and the economic: Assessing the global market impacts of soil erosion,

in: Land Use Policy – vol. 86, July 2019

11 Pasquale Borrelli, David A. Robinson, Panos Panagos, Emanuele Lugato, Jae E. Yang, Christine Alewell, David

Wuepper, Luca Montanarella, Cristiano Ballabio, Land use and climate change impacts on global soil erosion by water, in:

PNAS – Proceedings of the National Academy of Sciences of the United States of America – vol. 117, issue 36, August 2020

12 – 13 IPBES – Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, Assessment report

on land degradation and restoration (2018) – edited by Luca Montanarella, Robert Scholes, Anastasia Brainich, available

online @ www.zenodo.org/records/3237393

[1] David C. Coleman, Mac A. Callaham Jr., D. A. Crossley Jr., Fundamentals of Soil Ecology – 3rd edition, ed. Academic Press, 2018

[2] Hongwei Liu, Laura E. Brettell, Zhiguang Qiu, Brajesh K. Singh, Microbiome-Mediated Stress Resistance in Plants, in: Trends in Plant Science – vol. 25, issue 8, August 2020

[3] Ioannis A. Stringlis, Ke Yu, Kirstin Feussner, Ronnie de Jonge, Sietske Van Bentum, Marcel C. Van Verk, Roeland L. Berendsen, Peter A. H. M. Bakker, Ivo Feussner, Corné M. J. Pieterse, MYB72-dependent coumarin exudation shapes root microbiome assembly to promote plant health, in: PNAS – Proceedings of the National Academy of Sciences of the United States of America – vol. 115, issue 22, April 2018

[4] Dilfuza Egamberdieva, Faina Kamilova, Shamil Validov, Laziza Gafurova, Zulfiya Kucharova, Ben Lugtenberg, High incidence of plant growth-stimulating bacteria associated with the rhizosphere of wheat grown on salinated soil in Uzbekistan, in: Environmental Microbiology – vol. 10, issue 01, January 2008

[5] Shamayim T. Ramírez-Puebla, Luis E. Servín-Garcidueñas, Berenice Jiménez-Marín, Luis M. Bolaños, Mónica Rosenblueth, Julio Martínez, Marco Antonio Rogel, Ernesto Ormeño-Orrillo, Esperanza Martínez-Romero, Gut and Root Microbiota Commonalities, in: Applied and Environmental Microbiology – vol. 79, No. 01, December 2013

[6] Rodrigo Mendes, Jos M Raaijmakers, Cross-kingdom similarities in microbiome functions, in: The ISME Journal – Multidisciplinary Journal of Microbial Ecology – vol. 9, February 2015

[7] Andrew L. Neal, Aurélie Bacq-Labreuil, Xiaoxian Zhang, Ian M. Clark, Kevin Coleman, Sacha J. Mooney, Karl Ritz, John W. Crawford, Soil as an extended composite phenotype of the microbial metagenome, in: Scientific Reports – vol. 10, June 2020

[8] Max Roser, Hannah Ritchie, Pablo Rosado, Food Supply, data source: UN Food and Agriculture Organization (FAO) – available online @ www.ourworldindata.org/food-supply

 

[9] Pasquale Borrelli, David A. Robinson, Larissa R. Fleischer, Emanuele Lugato, Cristiano Ballabio, Christine Alewell, Katrin Meusburger, Sirio Modugno, Brigitta Schütt, Vito Ferro, Vincenzo Bagarello, Kristof Van Oost, Luca Montanarella, Panos Panagos, An assessment of the global impact of 21st century land use change on soil erosion, in: Nature Communications – vol. 08, December 2017

[10] Martina Sartori, George Philippidis, Emanuele Ferrari, Pasquale Borrelli, Emanuele Lugato, Luca Montanarella,

Panos Panagos, A linkage between the biophysical and the economic: Assessing the global market impacts of soil erosion, in: Land Use Policy – vol. 86, July 2019

[11] Pasquale Borrelli, David A. Robinson, Panos Panagos, Emanuele Lugato, Jae E. Yang, Christine Alewell, David Wuepper, Luca Montanarella, Cristiano Ballabio, Land use and climate change impacts on global soil erosion by water, in: PNAS – Proceedings of the National Academy of Sciences of the United States of America – vol. 117, issue 36, August 2020

[12]

[13] IPBES – Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, Assessment report on land degradation and restoration (2018) – edited by Luca Montanarella, Robert Scholes, Anastasia Brainich, available online @ www.zenodo.org/records/3237393