The Secret Life of Mycorrhiza

Why live plant roots are best at sequestering carbon.

“Not only is rebuilding carbon-rich topsoil a practical and beneficial option for productively removing billions of tonnes of excess carbon dioxide from the atmosphere, but when soils gain in carbon, they also improve in structure, water-holding capacity and nutrient availability.

Understanding the soil building process is therefore of fundamental importance to the future viability of agriculture.”

From Liquid Carbon Pathway by Christine Jones, PhD. Australian Farm Journal Edition 338 3 July 2008

Two of the key tenets of regenerative agriculture are to keep the soil covered (“armored”) and to keep living roots in the soil as much as possible. But did you know there was a difference in the carbon laid down in the soil between composted material and living roots? I didn’t.

This article made clear to me WHY cover crops are so important. No-till, mulching and compost are a great start and play an important role in reducing moisture evaporation and adding nutrients, but nothing beats live plant roots.   

The secret is in the interaction between live plant roots and amazing soil microbes known as mycorrhizal fungi. When a healthy plant photosynthesizes (converts sunlight into energy-rich compounds), it exudes soluble (liquid) carbon from its roots. The mycorrhizal fungi feed on this liquid carbon, growing extensive networks that access and transport water and nutrients such as nitrogen, phosphorous and zinc back to the plant. They can even connect individual plants from different species! (Another reason why plant species diversity is another principle of regenerative agriculture).

A large portion of the soluble carbon used by mychorrhizal fungi is resynthesized into highly complex polymers. These form a stable part of the soil matrix and the carbon can remain intact for hundreds of years, reaching well beyond the top inch or two of the soil surface.

By comparison, the type of fungi that survive in conventionally managed agricultural soils are primarily decomposers and live on decaying organic matter. These are also the fungi that live in the top layers of mulch and compost. This decomposed carbon differs from the mycorrhizal carbon in that it is simpler in structure and much more easily converted to CO2.

It is noteworthy that application of external fertilizers, pesticides and fungicides drastically diminishes the presence of mycorrhizal fungi in the soil. The paper’s author summarizes it well:

“Every 27 tonnes of carbon sequestered biologically in soil represents 100 tonnes of

carbon dioxide removed from the atmosphere. …If all farmland was a net sink rather than a net source for CO2, atmospheric CO2 levels would fall at the same time as farm productivity and watershed function improved. This would solve the vast majority of our food production, environmental and human health‘problems’.”

This cool YouTube video explains more about mycorrhizal fungi

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Interested in learning more? I read about this through the Understanding Ag RegenAg 101 course.