One of the great benefits of arbuscular mycorrhizal fungi (AMF), together with its army of associated microbes, is that it can build soil structure like nothing else.
It does this with a compound it manufactures called glomalin, only discovered in 1996 by ARS soil scientist Sara Wright. It is a carbohydrate-based "soil glue" that contains 30-40% carbon. Glomalin is the substance that creates clumps of soil granules called aggregates. These are what add structure to healthy soil. They also keep other stored soil carbon from escaping.
Technically, glomalin is considered a glycoprotein, which stores carbon in both its protein and carbohydrate (glucose or sugar) subunits. Because it stores so much carbon, glomalin is increasingly being included in studies of carbon storage and soil quality.
Recently, researchers have discovered some soil microbes also produce compounds similar to glomalin. That information is hard to track down, but the news implies complexity of life continues to have high value.
Further, scientists have found glomalin weighs from 2 to 24 times more than humic acid, which is the byproduct of decaying plants that once was thought to be the main contributor to soil carbon storage. Now scientists say humic acid contributes only about 8% of soil carbon.
Glomalin is an amazing material scientists say is actually difficult to break down. AMF produce glomalin to coat hyphae to keep water and nutrients from getting lost on the way to and from the plant.
Glomalin is extremely “tough”. It is resistant to microbial decay (lasting at least 10 to 50 years) and does not dissolve easily in water. Glomalin is soluble at high temperatures (250 degrees F). These properties make it a good protector of hyphae and soil aggregates.
When a hypha stops transporting nutrients, scientists think glomalin sloughs off onto surrounding soil particles. Hundreds of meters of hyphae can grow throughout a small sample of soil, resulting in the production of huge amounts of glomalin, therefore very stable, erosion-resistant soil.
One recent study helps show the importance of management to develop more glomalin.
Glomalin concentration and aggregate stability were examined through three years during conversion from conventional tillage (P-T) to no-till (N-T) corn. Researchers also compared this with a perennial grass that grew undisturbed for 15 years as a buffer around the plots.
They say increases in soil stability and glomalin formations yearly. Yet in three years neither had approached what they found in the undisturbed grass.
This shows two things:
1. Glomalin and soil stability increase slowly over time with improved soil management.
2. The agent of glomalin formation -- arbuscular mycorrhizal fungi -- forms slowly over time with improved soil management.
Note in the chart there was no increase in glomalin or soil aggregate formation in the plowed field plots.
Higher levels of glomalin give greater water infiltration, more permeability to air, better root development, higher microbial activity, resistance to surface sealing (crusts) and to erosion (wind/water).