Beneficial soil microbes and the soil food web

Learn about the microorganisms that feed all plants

Bacteria and fungi are fed directly by plant exudates (photosynthetic sugars and other nutrients) and organic matter (decomposing plant and animal remains). Fungi and bacteria also have powerful enzymes and acids capable of breaking down even rock! In this way they release minerals from parent rock material and the mineral component of soil (sand, silt and clay), which they incorporate into themselves. When fungi and bacteria are then consumed by other creatures like protozoa and nematodes (see below), and larger animals like earthworms, they are broken down and excreted as poo of their “predators.” The poo produced by the consumption of fungi and bacteria is in fact excess nutrients, which the predators can’t use. This amazing poo made up of broken down bacteria and fungi becomes the natural source of plant available nutrients (fertiliser). This wonderful system has been termed the Poop Loop!

Root symbiotic or mycorrhizal fungi, actively exchange minerals like Phosphorous, Sulphur and Nitrogen for photosynthetic carbon from the plant. It has been shown that plants “requests” particular minerals from bacteria and fungi, “rewarding” these microbes with particular nutrients that they prefer. So in effect, the plant selects the exact microbes that will provide it with its required nutrients.

Now meet the team of the soil food web and their specific roles in plant growth:

Plant associated bacteria

Bacteria are the most nutrient rich organisms on Earth. When they are consumed by other organisms, the excess nutrients they provide are released by their “predators” in plant available form. Some bacteria fix atmospheric nitrogen in root nodules of legume plants such as cow pea, beans, peas and lentils. This N is taken up by the plant and when plant matter it is broken down by bacteria and fungi, this nitrogen again becomes available to growing plants. The tiny comma shaped specs in the image are bacteria.

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Plant beneficial fungi

Can be symbiotic - living within plant root tissue, providing and exchanging nutrients for photosynthetic exudates (sugars, amino acids and other nutrients).

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Free living decomposer fungi organic matter dropped by plants storing those nutrients until they are consumed. Fungal grazers like nematodes, springtails, earthworms and other invertebrates, release N, P, S and other plant available nutrients on tained in the fungi they consume.

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Protozoa

Unicellular microscopic animals including amoebae and flagellates, which consume bacteria releasing excess plant available nutrients.

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Beneficial nematodes

Microscopic worms have different food preference, some feed on bacteria, some on fungi, and some on other nematodes especially parasitic root nematodes.

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This nematode is pooing out digested bacterial biomass, which directly feeds plants!

To learn more about the amazing creatures that must be present in your soil to support healthy plant growth or how to cultivate them, contact me at

loveoursoils@gmail.com⁠

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