A brief history of the fungi-to-bacteria ratio
Knowledge of not only the science, but also its history, is important for any grower considering the transition
Out there in the world at large, as any Soil Food Web professional can tell you, awareness and understanding of the science and history behind the SFW approach are still gaining momentum.
SFW professionals often serve as educators, communicating to their clients the basic structure of soil ecology – how nutrients cycle from one microbial group to another, and how the makeup of the larger community correlates with natural-area succession.
There are countless scientific and real-world case studies that prove without a doubt that Dr. Ingham’s Soil Food Web Approach to soil management produces higher levels of soil microbes and, consequently, higher yields and healthier plants and animals. Much of it by Dr. Elaine herself.
Evidence supporting the scientific validity and real-world benefits of the Soil Food Web approach is overwhelming, yet competing scientific endeavors have gotten most of the attention. And so lots of plant growers, their efforts having focused for so long on the mineral-chemical aspects of soil, now find themselves curious – what’s our understanding of the dynamics between bacteria and fungi? How do their relative abundance in soil – expressed in the fungi-to-bacteria ratio (F:B) – correlate with different plant communities, which come to thrive at different stages in the development of an ecological system? How, and when, did our science develop around all this?
Why do we measure F:B Ratios?
Fungi and bacteria hold the importance that they do because they are nature’s only primary decomposers. Of all organism types on Earth, they are the only major groups that make enzymes capable of separating materials into their constituent compounds. This means that nutrients cannot begin cycling through the food web without them.
To learn more about the agricultural crisis that has been caused by the killing off of soil bacteria and fungi, watch this video.
History of the F:B ratio
Our modern understanding of the importance of soil fungi relative to bacteria traces back to the mid-20th Century, when ecologists began focusing on how nutrients cycle through the floral and faunal communities of natural areas. There had already been a general awareness that bacteria and fungi played roles in decomposing organic matter, ever since researchers began noticing these two groups of organisms in plant- and animal-tissue infections. These observations had evolved into a broader study of pathogens and their remedies, one result of which was the world’s first antibiotic treatment, derived from the fungus Penicillium in the 1930s. In farming systems, the study of soil microbes has focused on detrimental bacteria, fungi, and nematodes that appear to attack plants, along with certain beneficial counterparts that could help control them, including the Pseudomonas and Bacillus genera commonly used today.
By the 1960s, the scientific community was developing a fuller appreciation of how decomposers mobilize nutrients for consumption by life forms higher up the food web, and had begun to explore natural systems to understand this process. In areas such as grasslands and riparian zones, scientists investigated the decomposition of specific organic materials, such as tree leaves. Researchers identified the various fungi on deciduous leaves and noted how their populations changed during the low temperatures of autumn, when those leaves fell to the ground and began decomposing.
For some time, it was assumed that fungi played significant roles only in terrestrial systems, as aquatic conditions were thought to support only bacteria. But in the mid-1970s, it was discovered that, even underwater, fungi not only appeared to perform much of the decomposition but also played specific roles that bacteria did not. Researchers in Canada showed that fungal communities, dominated by certain genera depending on the season, encouraged invertebrates to feed on plant material colonized by those fungi. Research in the US showed similar patterns. Studies like these revealed not only that fungi played important roles in the cycling of nutrients through the food web, but also that a balance between the two decomposers was ubiquitous in natural systems.
It was in the late 1970s that this concept of the relative densities of nature’s two decomposers began to find its way into cropland research. A study in Poland showed that nutrient cycling in the soil of a rye-potato rotation was dominated by bacteria, with protozoa and nematodes that appeared to consume them. Meanwhile, methods were being developed to quantify microbes, using concepts and techniques such as cellular respiration and direct microscopy.
The subject advanced into the next decade through studies, such as one in the US, indicating that bacteria dominated in plowed fields, while fungi dominated in no-till fields. This study also observed the immobilization of nutrients through biological means, as expanding bacterial and fungal communities consumed nitrogen and other plant nutrients, using them to build larger communities, thereby leaving less to feed plants. This led to the observation that under tillage, plants absorbed more of the nutrient products farmers applied, as soil turning left fewer live microbes to consume them. It also set the stage for future understanding of how those nutrients might subsequently be freed from those same microbes and made available to plants. And this is where Dr. Elaine’s work came in: building our understanding of nutrient cycling through the Soil Food Web and showing that farmers only need those nutrient products in the first place because the microbes necessary to keep plants healthy are missing from the soil.
Almost as far back as mid-century, it had been known that nutrients could be mineralized (converted from organic to inorganic form, allowing plants to absorb them) through the activity of microbes, and that while this microbial activity was dominated by bacteria and fungi, there was also some contribution from the fauna that grazed on them, like microarthropods. That understanding developed slowly until the 1980s, when it became apparent that those grazers – more notably protozoa and nematodes – might be playing a larger role than previously understood.
Dr. Elaine, who later established the Soil Food Web School, contributed to this research throughout the 1980s and 1990s, building on our understanding of nutrient cycling via pathways based on the relative densities of bacteria and fungi. These studies took place in various environments, including grasslands, prairies and conifer forests, contributing greatly to our modern understanding of how the food web develops in soils that remain undisturbed, allowing the successional process to run its course. Meanwhile, other denizens of the biological community develop alongside them, all of it contributing to the process of natural-area succession.
Beyond the nematodes that attack plants’ roots, so familiar to researchers going back decades, it turned out there were also nematodes that ate other things, including bacteria, the most nitrogen-heavy of all Earth’s organism types. Unable to use all that nitrogen, bacteria-feeding nematodes secrete much of it as waste, now mineralized, so it’s water-soluble and ready for plants to absorb. Protozoa, namely amoebae and flagellates, do the same thing. Still other nematodes feed on fungi, whose secreted nitrogen is weighted more toward ammonium, a molecule distinct from the nitrates more readily produced by bacteria. Ammonium better supports plants showing up later in the successional timeline, including most of those grown for agricultural purposes.
And nematodes eat more than just bacteria, fungi, and plants’ roots. They also consume larger prey, such as protozoa and even other nematodes, representing successive levels of nutrient cycling. Once Dr. Elaine began adding her own contributions to the scientific record, then spreading the word through her work with growers and students, a whole new world of understanding opened up. Now, we know what can happen when soils undergo successional development – through an altered fungal-bacterial balance – and nutrient-cycling activity: plants achieve truly well-rounded nutrition and health, allowing their physiological functions to work as nature intended. This means no more pest or pathogen infestations; it means a plant that can fulfill its potential for productivity and quality, producing the most nutrient-dense food possible.
All of these factors can contribute to an improved economic situation for any farmer, let alone to making life on Earth better overall. But it can require a significant shift in how things are done in the field, and it’s difficult to embark on such a journey without the confidence that comes from knowledge – not only of the current science, but of how the scientific record shows the development of our understanding through the decades.
Following in the footsteps of Dr. Elaine, the consultants who have graduated from the Soil Food Web Foundation’s school have helped hundreds of plant growers of all scales pursue just such a transition. But obviously, the work is far from over. Popular awareness may still be limited, but it’s growing fast, driven in large part by the work of Dr. Elaine’s school, which interprets and communicates the science to farmers, gardeners, groundskeepers, and anyone else who grows plants. Soon will come a day when most folks know the roles played by fungi and bacteria just as well as the importance of nitrogen or photosynthesis. That’s when we’ll know we’ve really gotten somewhere.
