The following is an excerpt from The Guardian.
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, when they suggested 25% of life was soil-based.
The paper, 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, 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 is 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 can 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. (Continued…)
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