Why Does Soil Smell So Good?
Chances are you’re unaware of the word “geosmin,” but your body’s sense of smell knows precisely what it is. Imagine an early spring day, and you’re greeted with a pleasing, earthy aroma as soon as you step outside.
The smell of the soil was first looked into back in 1891 with little success or necessity at the time. It wasn’t until 1965 that researchers N.N. Gerber and H.A. Lechevalier discovered the main compound and were able to isolate it, naming it “geosmin” (“Geo” Earth; “Osme” = Odor).
According to Phys.org, “Geosmin is the soil-based compound that gives the evocative, earthy smell so characteristic of spring. It’s best appreciated after recent rainfall or while digging. The human nose is so sensitive to the compound that it is detectable at one hundred parts per trillion. In other words, we can sense geosmin better than sharks can detect blood.”
So why does this odor exist? Researchers have found the unique relationship between a soil bacteria known as Streptomyces and a tiny six-legged insect called the springtail (Collembola) holds the answer.
Streptomyces are a well-regarded bacteria that have been used globally to create some of the world’s most effective antibiotics, producing geosmin in the process.
Research conducted in Sweden revealed that “The springtails were powerfully drawn to geosmin and to another earthy smelling compound produced by Streptomyces called 2-methylisoborneol (2-MIB),” according to Phys.org.
While other insects, such as nematodes and fruit flies, are killed when ingesting geosmin, springtails possess potent enzymes which detoxify the antibiotics produced by Streptomyces, making them safe to consume.
One of the study’s authors, Professor Mark Buttner of the John Innes Centre, says, “There is mutual benefit. The springtails eat the Streptomyces, so the geosmin is attracting them to a valuable food source. And, the springtails distribute the spores, both stuck on their bodies and in their feces, which are full of viable spores, so the Streptomyces get dispersed. This is analogous to birds eating the fruits of plants. They get food but they also distribute the seeds, which benefits the plants.”
While you probably won’t remember the term geosmin the next time you go hiking in the woods or dig holes in your garden bed, it’s the underground activity of the springtails and Streptomyces chemically communicating and enabling that unique, earthy smell to permeate and spread to soils across the globe.
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