Fungi Vs Bacteria
Over the weekend, I have been at work analyzing soil samples under the microscope. Today we are looking at a sample from the root zone of a client’s diseased tomato plant.
Looking under the microscope and seeing what organisms are present allows us to get a better understanding of how healthy the soil is. A healthy garden soil should have a relative balance of beneficial fungi and bacteria, which keep pathogens in check. In exactly the same way probiotics aid human health, beneficial organisms in your soil help to protect your plants from infection.
The complex interactions between all of these organisms is known as the “Soil Food Web.” A food web is simply a more complete representation of what most people know as a food “chain”, as illustrated in this diagram provided by the Natural Resource Conservation Service:
As you can see, these microscopic critters are not only important to the health of your soil, but literally support all life on Earth! Without them there is no food for insects, without which there is no food for birds, and so on. With this understanding, its obvious that we should utilize organic gardening practices that protect these organisms, while limiting our use synthetic fertilizers, which not only harm the soil, but also pollute our rivers and lakes, causing toxic algae blooms. To make it worse, many of the organisms that are able to survive chemical fertilizer applications are the very pathogens that we are trying to suppress. Once the beneficial bacteria and fungi have been killed, plants can no longer access the complex nutrients microbes release into the soil, after which the landscape becomes dependent on chemical fertilizers. While its true that these synthetics provide plants with the basic nutrients they need to survive, they take away what plants need to truly thrive and ward off disease.
Now that you have a basic understanding of the soil food web and why we want to support it, its time to dive into our soil sample:
SOIL SAMPLE TAKEN FROM DISEASED TOMATO ROOT ZONE
Here we can see a piece of partly decomposed plant tissue surrounded by lots of bacteria, both rod shaped bacteria called bacilli, as well as round bacteria known as cocci. Both can be important decomposers that help to support plant growth and suppress pathogens. However, “bacilli” and “cocci” are classifications which encompass a wide range of bacteria species, many of which are also pathogenic and include staph (cocci) as well as anthrax (bacillus).
Here we see our first signs of fungal life in the soil sample: a germinating spore that was found floating around a piece of organic matter. I was actually able to watch the spore grow (and die) as you will see in the following images. Notice the faint shadows of rod shaped bacillus bacteria to the bottom right.
We can see nutrients (green) being delivered from the spore body into the fungal hyphae strand as it grows.
We begin to notice that the bacilli are moving towards the fungal strand.
After only a few minutes the spore grew significantly, but the bacillus bacteria began to congregate in larger numbers around it, eventually attaching to it.
Here, we see the green nutrient solution spilling out of the tip of the hyphae where the bacillus were able to penetrate the cell wall. At this point, the unidentified fungus completely stopped growing and became food for the bacteria.
Zooming out, you can see that the dead fungal spore was reaching for a piece of woody debris (dark shadow). Above it, amber colored soil particles containing mineral rich fulvic acids, byproducts of decomposed organic matter, are attached to a root fragment.
Other interesting finds in this sample:
The video above shows a predatory nematode that was observed preying on bacteria before becoming trapped by a bacterial biofilm.
The video below shows another soil predator, a rotifer, feeding on even more bacteria.
Overall, this sample paints a picture of a soil which is very bacteria rich, but lacking in fungal diversity. Bacterial soil indicates that some disturbance, either mechanical or chemical, has killed off the beneficial fungi. (Usually a result of tillage or repeated applications of synthetic fertilizer)
Most garden vegetables prefer a balanced ratio of fungi to bacteria, whereas fast-growing weeds prefer bacterial, and trees prefer fungal soils. In this case, we would solve the client’s issue by inoculating the soil with high quality compost, or compost tea, verified by our microscopic survey to be rich in beneficial fungi.
If you are in Southeast Louisiana and want to learn more about the condition of your soil’s food web, and what we can do to help you improve it, you can contact Songbird Regenerative by clicking the “contact” button at the top of our page.