[Soil is estimated to be home to 90% of the world’s fungi, 85%
of plants and more than 50% of bacteria, making it the world’s most
species-rich habitat ]
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MORE THAN HALF OF EARTH’S SPECIES LIVE IN THE SOIL, STUDY FINDS  
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Phoebe Weston
August 7, 2023
Guardian
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_ Soil is estimated to be home to 90% of the world’s fungi, 85% of
plants and more than 50% of bacteria, making it the world’s most
species-rich habitat _

Holacanthella spinosa, a genus of giant springtail that lives in the
soil, Andy Murray/PNAS

 

More than half of all species live in the soil, according to a study
that has found it is the single most species-rich habitat on Earth.

Soil was known to hold a wealth of life, but this new figure doubles
what scientists estimated in 2006
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when they suggested 25% of life was soil-based.

The paper [[link removed]],
published in the journal Proceedings of the National Academy of
Sciences, found it is home to 90% of fungi, 85% of plants and more
than 50% of bacteria. At 3%, mammals are the group least associated
with soils.

“Here, we show that soil is likely home to 59% of life including
everything from microbes to mammals, making it the singular most
biodiverse habitat on Earth,” researchers write in the paper, which
is a review of existing literature. The actual figure could be even
higher as soils are so understudied
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they say.

Before this study, scientists did not know what the most species-rich
habitat was, says the lead researcher, Dr Mark Anthony, an ecologist
at the Swiss Federal Research Institute for Forest, Snow and Landscape
Research. “In my research circle, many suspected it should be soil
but there was no evidence.”

He added: “Organisms in soil play an outweighed impact on the
balance of our planet. Their biodiversity matters because soil life
affects climate change feedbacks, global food security, and even human
health.”

Soil is the top layer of the Earth’s crust and is composed of a
mixture of water, gases, minerals and organic matter. It is where 95%
of the planet’s food
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grown yet it has historically been left out of wider debates about
nature protections because we know so little about it. One teaspoon
of healthy soil
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contain up to a billion bacteria and more than 1km of fungi.

Researchers used the rough estimate of there being about 100bn species
in total. They then used theoretical estimates and data analysis to
work out what fraction of those species were found in the soil. They
defined a species as living in the soil if it lived within it, on it,
or completed part of its lifecycle in it. Other habitats they looked
at include marine, freshwater, the ocean floor, air, the built
environment and host organisms such as humans.

There is a large error range of 15% with the estimate – so the
average prediction could in theory be as low as 44% or as high as 74%.
For some groups the range was large – for bacteria, estimates ranged
between 22% and 89% living in the soil.

Anthony said: “What actually surprised me the most was the sheer
challenge of this undertaking, and how much variation there is to our
estimates for many large groups, particularly bacteria and viruses,
the two most diverse forms of life on Earth.

“Keeping that in mind, our estimate is really a first attempt to
organise existing global richness albeit with quite a large error to
many of the estimates. While true diversity lies somewhere within this
range, our effort is the first realistic estimate of global diversity
in soil, and we need it to advocate for soil life in the face of the
biodiversity and climate crises.”

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Down to Earth newsletter
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 A third of the planet’s land is severely degraded and 24bn tonnes
of fertile soil are lost every year through intensive farming alone,
according to a UN-backed study, the Global Land Outlook
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Pollution, deforestation and global heating also damages soil.
Adopting less intensive agricultural practices, greater regulation of
non-native invasive species, and increasing habitat conservation will
all help increase soil biodiversity, researchers say. Practices such
as soil transplantations could also restore microscopic lifeforms in
soil.

Dr Roy Neilson, an ecologist from the James Hutton Institute in
Dundee, who was not involved in the research, said: “It is
extraordinarily difficult to enumerate soil biodiversity … The
approach taken in this study arguably generates the current best
estimate of global soil biodiversity.

“However, as the authors note, generating these estimates has been
challenging and they are transparent as to the level of robustness of
their data, which in turn highlights areas for future scientific
investigation,” said Neilson, who is an author on the British
Ecological Society’s upcoming report on regenerative agriculture.

Phoebe Weston [[link removed]] is a
biodiversity writer for the Guardian. @phoeb0
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* extinction
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* mass extinctions
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* biology
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