Carl Sagan said in the Cosmos series, “if you wish to make an apple pie from scratch, you must first invent the universe.” What he means is that if we want to make or understand a thing, we have to understand that thing exists within a context. The context can change based upon the information we have, the biases we hold, and/or our perceptions, affecting how we experience reality. The scientific method is a deliberate attempt to move past the limitations of human perception to understand reality, as it truly exists. This has revolutionized some concepts and understandings well beyond what the beliefs earlier people held about the nature of the universe, especially about plants and animals. For example, most people now know that certain microorganisms cause specific diseases. This is the first in a series of essays about the soil ecosystem, Fungal lifestyles, and evolution.
When the rains come, mushrooms visit our gardens, peering at us through the flowers reminding us of the mysterious world just below the soil surface. What are they doing there? Are they hurting my plants? Can I eat them? However, it’s hard to talk about the relationships plants and fungi have without telling the full story of the soil because plants and fungi are but two actors on a stage and the story would be incomplete without all the characters. I also hope that this class will help everyone be better gardeners in general and feel more integrated into the ecosystem they live in.
https://www.nrcs.usda.gov/Internet/FSE_MEDIA/nrcs142p2_049822.jpg
Our paradigm for soil is shifting from one that understands the soil as non-living, a purely chemical world in which plants feed on available ions, to an understanding of the soil as an ecosystem, teeming with life. Fungi, as well as the plants, play a key role in guiding the development of the soil, with fungi in particular making nutrients bioavailable to the rest of the system. However, there are many dancers in the ballet of the soil, all playing critical roles. Bacteria fix nitrogen from the air, while protozoa, nematodes, earthworms, and arthropods subsist upon and redistribute these nutrients throughout the soil. Animals also play a role in this drama that Dr. Elaine Ingahm has dubbed “The Soil Food Web.” The story is one of predation and destruction as well as cooperation and regeneration. It’s a story in which humans have forgotten their role and we’re now relearning our part.
https://www.jswcd.org/soil-texture
The setting for our drama is also the place where the story begins. Billions of years ago water covered the earth and minerals dominated the land. Life began to develop and flourish in the water. Slowly organisms developed ways to protect themselves from drying out in the air and began to spread onto land. They were also carried far in land on the wind and in storms, sometimes landing in places favorable to their survival; others were not so lucky. Some of these organisms could demineralize the rocks they were growing on, releasing valuable nutrients from the rocks. Wind and water also break down the rocks through friction, creating smaller and smaller particles. These mineral particles are either sand, silt, or clay and their ratios tell us important information about how water will interact with soil, for example it will drain quickly if it's predominantly sand or quickly become waterlogged if it's predominantly clay. This is where others talking about the soil would begin talking about N-P-K and other macro- and micro- nutrients, however this is not that kind of talk. All the nutrients that plants need to grow already exist around in the soil or in the surrounding environment, they’re just not readily available for the plant. This is what they test for in a soil test, the available nutrients in the soil, and some soil labs will also give recommendations on the amounts of available ions one needs to add to a soil. But that begs the question, how does the old growth forest or the wild-prairie flourish without the ability to directly access the nutrients they need to survive? The organisms of the soil food web, or our cast of dancers, breakdown and make them available.
Hericium coralloides in Bryan, TX. Photo by Author
Beyond the spatial setting for our ballet, we must also address the temporal element. Ecosystems develop successional stages (though as with most things in nature these stages don’t have a distinct boundary but transitionally along a gradient). As I just mentioned, the surface of the earth not covered by water was all rock but when we look around us we know that this is no longer the case. There are forests and grasslands that cover the planet, and even in the most extreme environments, such as deserts and the arctic, have a layer of soil and organisms that utilize that layer. As time passes, this layer grows deeper and deeper as more and more nutrients and organic matter build up in the system leading the complex and diverse ecosystems we experience today. These pioneering organisms paved the way for not only animals to develop but plants as well. An ecosystem’s development and the organisms that survive there depend on the amount of light received annually, the distribution of the light (even night length throughout the year or not), the highest annual temperatures, the lowest annual temperatures, the annual precipitation rate, and the distribution of that precipitation throughout the year. These factors harmonize to allow the development of diverse ecosystems. Below the soil a similar process is taking place as the environment of the soil changes during the course of the day. Some soil organisms actively shape the soil environment to aid in their own and the other organisms they depend on for survival.
Dr. Jerry Glover next to a 14 foot tangle of Indian grass, compass plant, and big bluestem grass he grew. https://onpasture.com/2017/07/03/fourteen-foot-long-roots-thats-what-great-grass-farmers-grow/
While many different dancers move through the scenes of this ballet, one process has orchestrated it all and actually set the stage for the ballet’s current act to begin. Photosynthesis is the chemical process of turning light energy into sugars. Plants didn’t invent it but they have done beautiful things with photosynthesis and made it their own. The plant kingdom has spread across the globe and has many different species. And to reiterate, they took over the world without needing fertilizers or even watering from a person.
Since we experience plants above ground, sometimes we forget that there is an extensive portion of the organism below the surface also. When we bring plant roots into our discussion, we often focus on them as the site where the plant takes up water and other nutrients to the leaves. However this is only part of the story, most of the sugar produced during photosynthesis, the plant exudes into the soil. The plant custom manufactures exudates to attract specific beneficial bacteria, archaea, and fungi into a space around the root only a few millimeters wide called the rhizosphere. As the root grows it, sheds root hairs, upon which the bacteria, archaea, and fungi also feed. Their populations explode as the plant grows, attracting protozoa and nematodes that feed on the carbon sequestered by the bacteria, archaea, and fungi.
Gardeners are often familiar with nematodes as root feeder pathogens but there are also nematodes that feed on smaller nematode species, amoebae, flagellates, and ciliates. Tiny arthropods join the ballet next, feeding upon the bacteria, archaea, and fungi, as well as the root feeding nematodes. Earthworms travel through the soil, creating tunnels for water and air to infiltrate the soil, bringing organic matter from the surface feeling into the organic layer, and inoculating the soil with beneficial bacteria, archaea, and fungi. Larger arthropods join in, predating upon the smaller arthropods. Birds and animals the feed on the arthropods and worms or directly from the plants and fungi as well, carrying seeds and nutrients farther away than any the smaller organisms could
This all happens in the top several inches of the soil. Regardless of what the organisms eat, they all excrete “wastes” that other organisms also feed on. Or they simply scavenge the organic matter left in the wake of the feeding predators or shifts in climate. Over time this cycle builds up layer after layer of organic, creating new and better habitat for more plants to begin growing, furthering the cycle. As long as there are no major changes in precipitation and temperature, the system remains stable. This is how the Great Plains of North America was able to build up such rich “Bread basket” soils that were several feet deep in some places and how tropical rainforests sustain such diversity with notoriously “poor” soil.
Mismanagement of soils has been linked to the decline of many human settlements throughout history. The most relevant of these events to the United States is the Dust Bowl from 1930-1936. This occurred when a severe drought collided with farming practices and new gasoline powered tractors. The repeated disturbance of the soil displaced the deep root grass species leaving the Great Plains vulnerable to damage from wind and rain. As the United States and other developed countries continue to emit massive amounts of CO2 into the atmosphere and mistreat the soil through repeated tillage and application of industrial fertilizers and pesticides, we’ll continue to see more frequent and severe droughts and the “dust-bowlification” of not only the North American continent but across the globe.
However, one need not fret because in our understanding of the problem; lies our solution. By promoting a healthy soil ecosystem, we can actually use the soil as a carbon sink for the excess atmospheric CO2. The methods for doing so, on a large and back yard scale, will be covered in future essays. Before we get to that, first we’ll define Fungi and lay out their evolutionary history, then a deep dive into Basidiomycota (the branch of the Fungi evolutionary tree where we find the majority of the Fungi we eat), followed by an overview of Fungal ecology. After going through all that we’ll have laid much of the background info for why the methods for rehabilitating and protecting the soil will function. Not only will we be able to grow beautiful gardens and nutritious vegetables but we’ll also be informed on the best practices for industry, and prevent ourselves from falling for deceptive corporate greenwashing.
Resources:
Teaming with Microbes by Jeff Lowenfels and Wayne Lewis
Teaming with Fungi by Jeff Lowenfels
Teaming with Nutrients by Jeff Lowenfels
The Permaculture Student 2 by Matt Powers
Radical Mycology by Peter McCoy
The Soil Food Web by Elane Ingahm
The Next Dust Bowl by Joseph Romm
Soil as CarbonStorehouse: New Weapon in Climate Fight? By Judith D. Schwartz