Soil has a sweet tooth

Do you have a sweet tooth? If so, thank a plant! Plants have the superhero-like ability of turning an invisible gas, carbon dioxide, that is in the air all around us, into something we can hold in our hands and even taste — sugar! All the sugar you have ever eaten came from plants.

Why do plants make sweet sugars? For plants, animals and most organisms, sugars are the building blocks that make up our bodies and also the fuels which keep us energized!

The process of capturing a gas out of thin air and making it into sugar takes a lot of work! Sugars are energetically costly and thus valuable to any organism possessing them.

If sugars are so costly and difficult to make, then why would plants push the majority of their sugars (about 60%) out of their roots and into the soil? For plants to give away so much energy seems like an awful waste.

The answer — bacteria and fungi. We often forget about the most numerous organisms living on our planet. These creatures are everywhere, but most of them live right below our feet. For every tablespoon of healthy soil there are more bacteria than there are humans on Earth, and enough strands of fungi to stretch more than a football field. Bacteria and fungi (microbes) could never survive without plants feeding them all that valuable sugar.

But why do plants give so much of their hard-earned sugar to microbes? Because microbes have powers that plants do not possess. Microbes extract nutrients from the soil that plants cannot. A plant giving sugar to soil microbes is simply the plant’s way of paying for something that it cannot attain on its own. These unattainable goods are nutrients that plants need to live, similar to humans needing vitamins to grow strong.

Plants are capable of pulling some nutrients out of the soil, but they are far less efficient at the process than microbes. Microbes have the incredible ability of extracting essential nutrients from hard-to-reach places. They will even dissolve solid rock to find what they need! Plants grown without bacteria and fungal partners are small, weak and highly susceptible to diseases and other pests.

The relationship between soil microbes and plants is called mutualism. Mutualism is where two different organisms are more successful when they cooperate than when they work separately.

To help explain this let’s think about two construction companies. We will call them Y and Z. Company Y has a steady supply of wood boards but no nails to put them together. Company Z has plenty of nails but no wood. Neither company can build houses unless they share their resources. This is exactly how plants and microbes work together. Plants provide the wood boards (sugar), and microbes provide the nails (nutrients). They depend on each other.

Why is all this important? When we, as farmers and gardeners, foster the right conditions for microbes and plants to live in harmony then plants require much less attention, pesticides, and fertilizers from us humans. We can learn much by observing forests and prairies growing into beautiful and productive landscapes, not by any actions of people, but rather, the unsung superheroes on Earth, microbes.

— Mike Bredeson, Ph.D., a Litchfield High School graduate, is an agroecologist with Ecdysis Foundation, a nonprofit agricultural research firm.