A visible portion of the rhizosphere. Source.
If you had heard of glomalin, you are a better person than I am. Until a couple of months ago I wasn’t aware of its existence, which is close to sinful: it happens to be a very abundant protein in the soil rhizosphere, playing a key role in the soil’s mechanical properties and as repository of soil carbon. Glomalin is a glycoprotein (although the “glyco-“ may be overused here, as biochemical analyses suggest that it contains little in the way of sugars) that binds together silt, sand, or clay soil particles. By ‘supergluing’ the small, loose particles, this gooey protein makes larger granules or aggregates and protect the soils from the eroding forces of winds and water. So, where does glomalin come from? It is thought to be made by fungi, more specifically by members of the arbuscular mycorrhizal fungi, the Glomales (hence the name ‘glomalin’). The hyphae of these fungi synthesize glomalin as part of their stress response. They coat their outer surface with the protein to make a protective waxy coat that keeps the water and nutrients inside the cells. The glomalin coating also makes the fungal strings sticky so they bind soil particles, thus creating an protective ‘armor’ against environmental insults and microbial predators. Most importantly, the fungal “string bags” make soil aggregates. This improves water infiltration and retention in the soils and gas exchange, which makes them more fertile. For more information on glomalin click here.