10 October 2023
By: Amelia Genis
Nearly 60% of all life on Earth resides in the soil or is associated with it.
A recent estimate by microbiologists at research institutions in Switzerland, published in the journal PNAS, reveals that about 2 million insect and spider species inhabit the soil. This represents a third of this group.
They live alongside significantly fewer micro-arthropod (770) and worm species (6 000), but they still account for 98% and 63% respectively within their groups.
In contrast, only 3.8% of mammals live in the soil, while 85% of plants have roots in the ground.
However, the highest numbers are at the microscopic level, Prof John Quinton from Lancaster University writes in The Conversation about the work of Mark Anthony, Franz Bender and Marcel van der Heijden.
“The researchers estimate a staggering 430 million species of bacteria and 5.6 million species of fungi inhabit the soil. This represents more than half of all bacterial species and 90% of all fungi,” he says.
That these organisms are numerous is without doubt, but most important are the functions they perform. Small creatures such as earthworms and springtails break down organic material and incorporate it into the soil. Through this process, nutrients needed by plants are made available.
Mycorrhizal fungi grow in association with plant roots, anchoring themselves to extract nutrient-rich substances. In return, the fungi assist plants in accessing more nutrients.
Equally vital for agriculture are bacteria that fix nitrogen, usually in association with legumes. Rhizobia bacteria convert nitrogen gas in the atmosphere into compounds plants can use. Although similar compounds can be manufactured in factories, the process consumes a lot of energy.
Quinton writes that soil organisms also help bind the soil. “As organisms burrow into the soil, whether by digging, building nests, or as a means to anchor themselves, they contribute to soil structure.”
Good examples of this are termites that transform the soil by creating channels through which air and water can move, and roots and root hairs that bind the soil.
The incorporation of decomposed plant and organic material into soil also helps to hold it together and increases its water-holding capacity.
Soil minerals hold on to organic material and help to sequester carbon. Soil stores three times more carbon than plants and twice as much as the atmosphere.
These functions are typically carried out by different species as a sort of safety net because all species are not equally affected by environmental conditions such as droughts or floods.
Some species are more resilient than others, and as conditions weaken, those that are stronger can still perform these functions. This enhances the ability of an ecosystem like soil to withstand environmental shocks and recover from them.
Source: “More than half of life on Earth is found in soil – here’s why that’s important”, theconversation.com
