The most species-rich habitat on Earth is not oceans or rainforests. A recent study reveals that over 50% of Earth's species inhabit the soil, making it the most biodiverse habitat. This finding doubles the previous estimate from 2006, which indicated 25% of life resided in soil.
Soil Hosts 59% of Earth's Life
In the study, titled "Enumerating soil biodiversity" published in the journal PNAS, soil is believed to host around 59% of life, encompassing a wide range from microbes to mammals, establishing it as Earth's most biodiverse habitat.
Ecologist Mark Anthony from the Swiss agricultural research organization Agroscope and his team pointed out that soil is rich in minerals, gases, liquids, and organic material and that it covers much of the planet's surface. However, despite its significance, the knowledge about the living components within Earth's soil remains limited.
Anthony added that organisms within the soil wield a substantial influence on Earth's equilibrium. The diversity of soil life is crucial, as it influences climate change dynamics, worldwide food security, and even human well-being.
As the team explains in their study, soil is the uppermost layer of Earth's crust, which encompasses water, gases, minerals, and organic matter. Due to that, it serves as the foundation for 95% of the planet's food production.
However, due to its enigmatic nature, it has often been overlooked in discussions about nature conservation. Even though little is known about it, a single teaspoon of healthy soil can contain a billion bacteria and over a kilometer of fungi.
Aiming to estimate the proportion of Earth's species residing in soil, researchers used a rough approximation of 100 billion species and employed theoretical calculations and data analysis. Their definition of soil inhabitants included those living within, on, or completing parts of their lifecycle in soil.
Although the estimate carries a wide error margin of 15%, with predictions ranging from 44% to 74%, the study provides a first attempt to quantify global soil biodiversity, especially for diverse groups like bacteria and viruses. This assessment is vital for advocating for soil life amid the ongoing crises of biodiversity and climate.
Biodiversity Found Beneath the Soil
In their analysis of existing literature, Anthony and his team discovered that up to 88% of bacteria, 85% of plants, and 90% of fungi thrive within the delicate layer of soil. In contrast, only about 4% of the diverse range of mammal species, numbering around 6,500, inhabit this environment.
While the calculated biodiversity percentage of 59 (with a potential range of 15%) is likely an underestimate due to limited understanding of soil ecosystems, this estimation does not even encompass bacteria-invading viruses, which exhibit remarkable diversity and dominate the soil realm.
Among soil-dependent species, Enchytraeidae, small relatives of earthworms, top the list with 98.6% reliance on soil, primarily within the uppermost 5 cm, where they hunt bacteria, fungi, and organic material. Despite their prevalence, these creatures are relatively unknown beyond their use as fishing bait.
Unfortunately, soils across the globe are facing threats from erosion, fires, and pollution, with a report indicating that about 65% of Europe's soils are in an unhealthy state. Moreover, human-made alterations to the land above the soil have likely impacted the biological makeup and functioning of soils.
Anthony likens the situation to a census, suggesting that the findings should encourage increased efforts in soil conservation and restoration, areas that currently lack adequate attention.
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