→ What is the role of soil microorganisms in soil health and carbon sequestration?
Soil microbes are bacteria, fungi, protozoa, and others who support soil health in numerous ways. Some form mutualistic relationships with plants. The plants give them some of the carbon that they take from the atmosphere during photosynthesis. Others eat carbon-rich organic debris, and bring the carbon into the soil in a stable form. Some microbes eat other microbes, so the carbon gets cycled into the soil from their excretions.

Key players of soil health: meet the microbes

Who: bacteria, fungi, protozoa, nematodes, earthworms, and arthropods (OSU)

What: are the foundation of soil health, plant health, and soil carbon sequestration

When: all day every day

Where: the soil under our feet

Why: carbon is their favorite food

How: Well, we’ll get into that in the article…

Learn how these minuscule life forms have a colossal impact on your garden's health and productivity.

Oh, and they’re a major key in saving the planet too.

→ There are more microbes in a single teaspoon of soil than the entire human population!

Who gets to be a soil microbe?

Soil microbes are a group of organisms. in order to be a member of their amazing club, you’d need to be either a bacteria, fungus, protozoan, nematode, earthworm, or arthropod (OSU).

Soil bacteria

Soil bacteria are the most populous demographic in the soil microbe club. They are also the smallest in size (OSU).

There’s a wide range of characteristics within the realm of soil bacteria.

Some bacteria have a special relationship with certain plant species. An example of this is the bacteria that support legumes in “fixing” nitrogen in the soil (soil quality).

Similarly, some bacteria are the foundation of other nutrient cycles, such as phosphorus and sulfur.

Other bacteria are more generalists.

Soil bacteria can act as decomposers, and form soil aggregates, too (OSU).

Fungi

Fungi share a lot of same roles in the soil microbiome as bacteria.

They act as decomposers, specifically for tough organic matter like cellulose and lignin. They support nutrient cycling, too.

Like bacteria, some fungi can form mutually beneficial relationships with plants. These fungi are called Vesicular Arbuscular Mycorrhizae. In fact, around 90% of all plants have symbiotic relationships with mycorrhizal fungi.

Due to their root-level relationship with plants, fungi can actually prevent plant disease and delivery nutrients and water to plants, too.

Lastly, Fungi support soil aggregation to improve soil structure (DPI).

Protozoa

Protozoa are similar to bacteria and fungi in that they are decomposers and nutrient cyclers.

While they don’t contribute to other facets of soil health in the same way, they do provide another service to the soil: microbial population regulation.

Protozoa eat soil bacteria. In this way, they keep the bacterial population young. Believe it or not, this is a good thing because younger soil bacteria decompose organic matter more efficiently (New Phytologist, Britannica).

Arthropods (including earthworms)

Arthropods are decomposers, and they can support the formation of soil aggregates to improve soil structure. Earthworms, through their castings, are top-tier aggregate formers. Millipedes and ants are also examples of arthropods.

Their eating and pooping habits contribute to the nutrient cycle.

Arthropods regulate the activity of soil bacteria and fungi. For example, their movement through the soil, eating, and castings invite these microbes into the soil. As arthropods start the decomposition process, fungi and bacteria can help with the job.

-MDPI, Science Direct

Nematodes

Nematodes are nutrient cyclers. They eat bacteria and poop out the nitrogen in the bacteria as a plant-available form of the nutrient (eorganic).

Nematodes are excellent helpers in the decomposition process. Like protozoa, they eat soil microbes. They keep the microbial population diverse, which supports efficient decomposition (research gate).

They regulate microbial populations by eating different bacteria and fungi. Beneficial nematodes even eat root-feeding nematodes. This in turn supports plant health (rogitex).

→ Why are soil microbes so important in regenerative gardening?

Soil microbes perform many ecological services in the garden, especially related to organic matter and carbon sequestration.

Regenerative farmers and gardeners have two main goals: build soil health to grow more robust plants, and build soil health to sequester carbon.

Many of the regenerative principles - such as mulching, keeping the soil planted, and cover crops, all build organic matter levels in the soil.

According to Nature, organic matter is composed of soil microbes and decomposed organic materials.

Microbes and decomposed organic materials are very carbon-rich. The more organic matter present in the soil, and thus, the more microbes, the higher the soil carbon levels (CSU).

Other regenerative practices, such as no-dig methods, not disturbing the soil, and building up soil layers minimize damage to the soil microbiome and minimize carbon release.

→ Soil microbiota are the unsung heroes of carbon sequestration. In fact, they are the largest factor of soil carbon storage levels.

The soil microbes have a mutually beneficial relationship with plants in a really powerful way that also stores carbon in the soil.

As plants photosynthesize, they transform atmospheric carbon dioxide into sugars. These sugars are an energy source for the plant, but this carbon gets utilized by the soil microbes in different ways to make it store long-term in the soil.

And the carbon then goes on to enrich the quality of the soil and support more plant life. There’s a win-win situation here: the more carbon we sequester, the more fertile the soil is.

Here’s how carbon fixation works for each soil microbe type:

Fungi and carbon sequestration

Plants save some of those sweet carbon-rich sugars to give to fungi. Fungi have a mutually beneficial relationship with plants. In exchange for the carbon food source, they help the plant with nutrient and water uptake. Sometimes, they even protect the plant from disease.

As decomposers, fungi also break down organic matter and bring the carbon components into stable carbon in the soil.

The carbon is safely stored in fungal biomass in the soil.

-eos, boston university

→ Learn more about mycorrhizal fungi in our in-depth article here

Bacteria and carbon storage

Did you know that some soil bacteria actually can carry out photosynthesis, like plants? Cyanobacteria is one example. This process allows them to store carbon in their bodies. As they eventually pass away, the carbon stays in the soil.

Other bacteria have relationships with plants, such as nitrogen fixers. These bacteria also feed on carbon provided to them by the plants, and help keep it in the ground.

-bbc, nih

Protozoa and soil carbon

As soil microbiota population regulators, protozoa take in the carbon from these organisms. As they digest and eventually excrete their meals, the carbon is left behind in the soil.

Interestingly, the nutrients that the protozoa release can also activate other microbes that store carbon in the soil, which in turn, benefits the environment.

As I mentioned above, protozoa also keep the microbe population in check which actually makes it more efficient in carbon storage.

-science direct, science direct 2, grantome

Arthropods break down carbon in the soil

Arthropods are pro-level decomposers. They turn dead plants and animals to small, broken down pieces. This makes it simpler for other microbes to come along and continue the decomposition process. All of this means that the carbon originally found in the dead plants and animals gets placed into the soil.

Part of the reason why the carbon stays in the soil is because some arthropods, like worms, also help form soil aggregates. These aggregates make the soil more healthy and help the carbon to be stored long-term.

-PLOS, MDPI, Erika Young

Nematodes impact the carbon cycle

Nematodes work a bit differently in the soil carbon cycle. They act as triggers for other organisms to grow, and in turn, store more carbon in the soil.

For example, some nematodes eat the roots of plants, and this causes the plants to pump more carbon into the soil.

In turn, this carbon boost can make other microbes grow, which in turn means they can store more carbon in the soil.

Lastly, some nematodes eat other soil microbes, and then digest and excrete their nutrients into plant-usable forms. This means the plants grow better, so they photosynthesize more, and sequester more carbon.

-Science Direct, NIH

How to make microbes love your garden:

Give Microbes a Blanket of Food

Mulching is like tucking the soil in with a cozy comforter. It's a simple act with profound implications for carbon conservation.

Mulch helps with carbon sequestration by:

• Feeding Microbiota: As mulch breaks down, it becomes a feast for soil microbes, which are essential for converting organic matter into stable carbon forms within the soil (Springer).

Grow More Microbe Food

Cover crops are kind of like the essential night shift worker, getting the important work done and sequestering carbon when the “cash crops” are at home sleeping (likely in the pantry).

When fields would otherwise have nothing growing - which means, no photosynthesis, no well-fed microbes - these plants step in.

Here's how cover crops help sequester carbon:

• More Photosynthesis Time: For the carbon sequestration benefits of photosynthesis to occur, the soil needs to have living plants. Studies have proven that cover crops increase carbon storage in soils.
• Organic Matter Multipliers: Once they decompose, cover crops enhance the organic matter in the soil, another crucial element for storing carbon. SARE performed a study that showed that cover crops feed bacterial life, fungi, earthworms, and other soil microbiota. This increases carbon storage in the soil.

Don’t Panic, use Organic Inputs (fertilizers, etc.)

Conventional farming utilizes synthetic inputs that contribute to climate change in major ways. With 300 times the warming potential of carbon dioxide, nitrous oxide is released into the atmosphere with the application of synthetic nitrogen fertilizers.

Organic inputs are kinder to the atmosphere, waterways, and landscape as a whole.

Also, organic inputs work WITH our soil microbe heroes to deliver nutrients to the plants. In contrast, synthetic inputs bypass the microbes all together, and as the microbes become unnecessary, their populations decrease (Teeming with Microbes).

Go Poly…culture

Polyculture is when lots of plants are combined together. It’s the opposite of monoculture. Think of broccoli plants intermingling with nasturtium, pea plants, and oregano, in the same raised bed.

A study published in Nature Communications found that plant diversity increases soil microbial activity and soil carbon storage.

The research suggests that elevated carbon storage in high plant diversity areas is a direct function of the soil microbial community. More plants, more microbes, more carbon, more soil health.

Polyculture has other benefits too: with increased biodiversity comes less pest pressure, less disease, and a more robust soil microbiome.

Make compost, not war

The process of making compost in and of itself reduces the amount of methane emissions that your food waste would create if sent to the landfill.

It also has another benefit fo your garden - it’s that amazing microbe-rich organic matter we’ve been talking about!

As organic matter increases, the plants are able to grow better and actually sequester more carbon.

In fact, a 19-year study found that in semi-arid soils, compost addition was a major component of carbon storage potential.

Just say no to tilling and soil disturbance

Tilling and digging in the garden is the epitome of disturbing the soil, disrupting the soil microbiome, and exposing captured carbon back into the atmosphere.

This is why no-till farming and gardening is an essential part of carbon-smart strategies.

No-till gardens have other advantages, too - more water retention, robust fertility, and more soil microbial life.

Soil erosion is also caused by tillage practices. In fact, tillage was the main cause of the Dust Bowl nearly 100 years ago. So we are able to retain soil and prevent nutrient run-off when we go no-till (sound).

Soil Microbes - a regenerative gardener’s best friend

Soil microbes really do make the world a better place. In fact, their actions make our plant habitable. When you shift your focus from growing plants to building soil health, and then from building soil health to increasing soil microbe populations - then you’ve opened up a whole new world of carbon sequestration potential.

In this way, you turn your yard into a carbon sink. Imagine if every yard was increasing its soil microbe populations? This would be an amazing step towards climate change mitigation.

One of the books that influenced me to create this site was Climate Lyricism by Min Hyoung Song. In it, he asks us to imagine, and create “stupendously, wildly, deliriously better worlds.” And the way I see it, regenerative yards, public spaces, and farms are one wild way to accomplish this better world.

Now go out there and make some microbes happy!

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