Mysterious, Marvelous, Manipulative Microbes
Allen R. Williams, Ph.D
As regenerative farmers we pride ourselves in paying attention to the little things. Even the really little things like the microbes in the soil. When it comes to healthy soil, healthy plants,
healthy animals and healthy people, the little things do matter a lot. That is why our focus in food production starts not just the soil itself, but the tiny creatures residing in the soil that make a huge difference.
The world beneath our feet is incredibly diverse and complex, just as sophisticated and purposeful as anything we can point to above the soil surface. The tiny creatures that exist as microbes beneath our feet
are quite dynamic in nature, able to make spur-of-the moment decisions regarding trading or hoarding nutrients, rewarding plants that are generous to them, while punishing plants that are stingy,
and negotiating the best “deal” they can with the plants they interact with.
The magic of mycorrhizal fungi
I want to focus on one of those tiny creatures called mycorrhizal fungi. These are microscopic filamentous (threadlike) organisms that play an incredibly important role in the production of truly healthy,
nutrient-dense food. We are now discovering what a critical role mycorrhizae play in the food web cycle of life and what happens when mycorrhizae are not present in the soil in large numbers.
Amazingly, these creatures that are of such a high level of importance have been the least studied among all factors critical to agriculture and ecosystem health.
Mycorrhizal fungi are the lords of the world beneath the soil surface, in the subaquatic ecosystem that exists beneath our feet. The term mycorrhizae originates from the Latin word myco (fungi) and the
Greek word rhiza (root). Given the chance, they spread their feathery tendrils throughout entire fields connecting every plant in a web of mysterious and constant communication.
The fungal world beneath the soil surface is incredibly diverse, far more so than life above the soil surface. In fact, a single spoonful of healthy, microbially active soil contains more life than there are humans on earth.
It is a fantastically rich habitat. At any point in time, each individual plant can be trading sugars and fats with dozens of fungi and each fungi may be trading minerals with dozens of plants.
The picture below shows mycorrhizal fungi and their spores surrounding a plant root.
Photo: Sara Wright/U.S. Department of Agriculture
Mycorrhizal fungi attach themselves to plant roots via a sticky biotic glue called glomalin. This allows the fungi to trade nutrients with plants in a delicate exchange that eventually benefits us IF we don’t
interrupt this process. By design, mycorrhizae are far better than plant roots themselves at picking up minerals in the soil and transferring them to the plants for uptake. Most of the minerals in the
soil are bound and must be solubilized before they can be absorbed by plants. Mycorrhizae produce powerful enzymes that break those chemical bonds and allow the minerals to be transferred to the plant.
The mycorrhizae actually have selfish motives for doing this. They want to eat too. In exchange for plant root exudates that are loaded with carbon, the mycorrhizae pick up these minerals from the soil and feed the plants.
I call it the world’s oldest bartering system.
The biotic glues that attach the mycorrhizae to plant roots also serve a dual purpose to aggregate, or stick together, tiny soil particles in much larger clumps of soil (called aggregates) that then allow for
oxygen and water infiltration into the soil. Without these aggregates, rain tends to pond and pool on the soil surface and then run off, carrying tremendous amounts of topsoil, nitrates, phosphates,
and agricultural chemicals with it. As a result, flooding increases and drought is exacerbated. So, these tiny creatures serve as a mitigator to much larger, and even catastrophic events, such as severe
flooding and severe drought. Without their action in the soil, we suffer. When they are present in large numbers and highly active, we benefit.
More than a fungi, a plant’s best friend
The mycorrhizae extend the reach of the plant roots by 40-60 centimeters and increase their nutrient absorptive surface by hundreds of times. By greatly extending the reach of plant roots the plants
are able to access nutrients (minerals) and water that they otherwise would be unable to access. The figure below illustrates just how much mycorrhizae extend the reach of plant roots. The right side of the picture
depicts mycorrhizae attached to the plant root, significantly extending the ability of the root to reach minerals and water in the soil that it would otherwise be unable to reach. The left-hand side shows how limited
the plant root would be without the mycorrhizal association.
Mycorrhizae also interconnect plant roots between all the plant species that may be growing in a field. This interconnection forms an underground highway that can “feed” nutrients from one plant species to another.
These nutrients include the primary nutrients, such as nitrogen and phosphorus, that all plants depend on. Plants like legumes (clovers, alfalfas, peas, etc.) work in association with rhizobia bacteria to capture atmospheric
nitrogen and convert it into a form of nitrogen that plants can absorb and utilize. The mycorrhizae can transfer a portion of that nitrogen to other plants in the field that do not form associations with rhizobia.
Additionally, different plant species produce varying arrays of what are called plant secondary and tertiary nutrient compounds. These compounds often are medicinal in nature and confer disease and pest resistance
on other plants AND are also medicinal in nature to animals and humans. These secondary and tertiary compounds are transferred from plant to plant via the mycorrhizal highway. Without this occurring, plants are far
more susceptible to fungal diseases and to pest insects. In fact, mycorrhizal fungi are the principal immune system for plants against fungal root diseases. In the past several decades the use of fungicides by farmers has
increased significantly because typical agricultural practices, such as tillage, decimate mycorrhizal fungi populations. In addition, the fungicides used to combat plant fungal diseases are not target organism specific and kill
not only the target disease-causing organism but also the mycorrhizal fungi. As farmers we have been working against ourselves in this regard. When we damage the natural mycorrhizal fungi populations in the soil,
we create conditions where plants are more susceptible to fungal disease. We then spray fungicides to protect the plants from the fungal disease we further damage the mycorrhizal fungi.
This quickly becomes a vicious cycle that we find hard to get out of.
Giving mycorrhizae and microbes a chance
That is why we teach and practice regenerative farming principles. By reducing and eliminating tillage we stop the destruction of the mycorrhizal fungi, and by implementing practices such as diverse cover crops
instead of monocultures, coupled with the mycorrhizal stimulating effects of animal grazing impact, we not only reduce but even eliminate the need for fungicides. We escape the vicious cycle and turn things back over to Mother Nature.
Mycorrhizal fungi protect plants from drought through storage of water molecules inside plant roots. Because mycorrhizae actually can penetrate plant roots, they have a direct conduit to transfer water molecules to the plant roots for use in periods of dry and drought conditions. The picture below shows water molecules placed into a plant root by mycorrhizae filaments. Like many other functions performed by mycorrhizae there is a selfish motive involved. The mycorrhizae want to be fed during periods of drought, so by placing the water molecules inside plant roots they assure themselves that the plants have adequate survival to continue to feed root exudates to the mycorrhizae.
Source: Mycorrhizal Fungi: N Transfer. Dr. Amarathus. Crops.
Mycorrhizal fungi perform another critical function by “feeding” plants organic forms of nitrogen in the form of amino acids available in the soil.
This is a very important realization for farmers who rely upon heavy nitrogen fertilizer applications on a routine basis. This source of nitrogen has been almost wholly ignored within the agricultural sector, yet,
is readily available IF you have active mycorrhizal fungi working for you within your fields. The mechanism by which this nitrogen transfer occurs is rather simple: Mycorrhizal fungi penetrate the plant root structure,
capture nitrogen laden amino acids (organic N) from the soil and directly transfer them into the plant root (see picture below). This form of nitrogen is absolutely free and available as long as we facilitate the pathway.
Source: Mycorrhizal Fungi: N Transfer. Crop. Dr. Larry Aramanthus
The underground nutrient and information exchange
It is important to note that mycorrhizal fungi are not simply traders of nutrients but act as highly sophisticated processors of key information.
The principal role of plants is to capture solar energy from the process of photosynthesis, in the form of carbon dioxide, and convert that into energy-rich sugars and fats. Microbes are masters of capturing minerals in the soil through solubilizing-bound mineral. Plants need these minerals and microbes need the energy-rich sugars and fats. Instead of a constant standoff between plants and microbes, they have struck up deals to share and exchange these needed nutrients. More than 80% of all plants existing in the world today have developed relationships with fungi. Still others have relationships with bacteria in the soil. If we were to purge the soil of microbes, we would also purge the soil of plants.
Work performed by Toby Kiers and co-workers (https://doi.org/10.1016/j.cub.2019.04.061) shows that plants engage in “lively two-way conversations mediated by their underground collaborators” (microbes). She postulated that “through back and forth conversations, they increase the resilience of the whole community.”
When nodules on soybean plants were artificially surrounded by a nitrogen-free air supply, making the nitrogen-fixing bacteria useless to the plant, the soybean plant reacted by shutting off the oxygen supply to the bacteria. The plant surmised that the bacteria were being stingy with the nitrogen they had “fixed” from the atmosphere and punished the bacteria for not feeding that nitrogen to the plant (https://www.nature.com/articles/nature01931).
In another experiment, carrot roots and fungi were grown together in a petri dish divided into three equal compartments. Interestingly, in one compartment the carrot roots provided the fungi with more sugars than in the other compartments. The carrot that was willing to trade more sugar with the fungi received more fungal phosphorus in return.
We now know that in this delicate dance between plants and mycorrhizal fungi, plants can reward high-performing fungi with more sugars and punish poor performing fungi with less sugars. The fungi do the same, supplying plants that “feed” them more sugars with greater phosphorus and nitrogen, among other nutrients. In addition, mycorrhizal fungi can store or “hoard” nutrients when a plant is “paying” them well through the release of sugars. They actually wait for a better offer from either that plant or from other plants before they will release the nutrients.
These fungi can also move nutrients back and forth from “rich” regions in the rhizosphere to “poor” regions. In the poor regions the plants are willing to pay more for the nutrients carried by the fungi, especially phosphorus, and release more carbon-rich sugars. Where phosphorus is scarce, the plants are willing to strike a harder bargain with the fungi and give them more sugars in exchange for the phosphorus. Through this feedback system, soils that are phosphorus poor can quickly increase their phosphorus availability through this fully functioning mycorrhizal pathway. However, not only does the phosphorus flow from the rich areas to the poor areas, but there are nutrients flowing both ways at all times. Research has shown that nutrients oscillate back and forth through the mycorrhizal network every five minutes at precise intervals.
Enabling your silent, underground business partners
Soil microbes truly are the foundation of all health, both below the soil surface and above. Implementing agricultural practices that damage or destroy these soil microbes is only doing harm to ourselves and to all life around us. Conversely, implementing true regenerative practices that foster, facilitate, encourage, and stimulate these soil microbes provides immense benefit for humans and our surrounding ecosystems. If our soil is healthy, our crops are healthy, our livestock are healthy, we are healthy, our ecosystems are healthy, and our climate is healthy. These tiniest of creatures hold the key to solving the daunting issues we face today.. If we simply provide for them, they will provide for us. That is why we do what we do every day—show others how to grow and profit regeneratively.
The Land is Calling.
LIBERTAS LAND
Where the work of regeneration becomes the work of life.