The Chemistry Beneath Our Feet: How Soil Bacteria Shape the Atmosphere

by | Sep 21, 2026

A handful of soil contains an enormous microbial community.

Many of those microorganisms spend their lives dismantling material that falls onto the ground: dead leaves, roots, animal waste, sugars released by living plants, and the remains of other microorganisms.

For bacteria, this material is food.

For the atmosphere, bacterial metabolism is part of a much larger chemical cycle.

As soil bacteria consume, transform, and recycle organic matter and nutrients, they can release carbon dioxide, generate nitrogen-containing gases, consume atmospheric methane, and produce volatile compounds that move through tiny air spaces in the soil.

Decomposition is therefore not simply something happening underground.

It is part of the chemistry of the air above it.

Bacteria Help Return Plant Carbon to the Atmosphere

Plants remove carbon dioxide from the atmosphere through photosynthesis and use that carbon to build leaves, roots, stems, sugars, and other organic molecules.

Eventually, much of that material enters the soil.

Bacteria begin breaking those molecules into smaller compounds they can use for energy and growth.

When aerobic bacteria metabolize organic carbon in the presence of oxygen, respiration produces carbon dioxide.

That CO₂ moves through pores in the soil and eventually enters the atmosphere.

This process is part of soil respiration, which also includes respiration from plant roots and other microorganisms.

The carbon dioxide released by bacteria is not newly created carbon. It is carbon being returned to the atmosphere after previously passing through plants and the soil ecosystem.

Temperature and Water Control the Speed

Bacterial decomposition does not occur at a constant rate.

Temperature matters because bacterial enzymes generally work more rapidly within favorable temperature ranges.

Water matters because bacteria require moisture, but too much water can fill soil pores that normally contain oxygen.

A warm, moist, well-aerated soil may therefore support extremely active bacterial decomposition.

Cold or dry soil can slow it dramatically.

When heavy rain saturates the soil, the chemistry changes again because oxygen becomes scarce.

That shift from oxygen-rich to oxygen-poor conditions can completely change which bacterial reactions dominate.

Soil Bacteria Help Run the Nitrogen Cycle

Carbon is only part of the story.

Bacteria are central participants in the transformation of nitrogen compounds.

When organic material decomposes, microbial activity releases nitrogen into forms including ammonium.

Other microorganisms can then perform nitrification, converting ammonia or ammonium into nitrite and eventually nitrate.

Certain bacteria carry out important portions of this process.

Nitrification is useful because it produces forms of nitrogen that plants can use, but it can also generate small quantities of nitrous oxide, or N₂O.

Nitrous oxide is a powerful greenhouse gas and also participates in chemistry that destroys ozone in the stratosphere.

Agricultural soils receiving large quantities of nitrogen fertilizer can become particularly important sources.

When Oxygen Disappears, Denitrification Begins

Wet soil creates another pathway.

When oxygen becomes limited, some bacteria can use nitrate instead of oxygen as part of their metabolism.

This process is called denitrification.

Rather than converting nitrate in a single step, bacteria move it through several chemical forms:

nitrate → nitrite → nitric oxide → nitrous oxide → nitrogen gas

Ideally, the process reaches ordinary nitrogen gas, or N₂, which makes up most of Earth’s atmosphere.

But the pathway does not always run to completion.

Nitric oxide and nitrous oxide can escape from the soil before bacteria finish processing them.

The result is a direct bacterial connection between soil conditions and atmospheric chemistry.

Nitric Oxide Can Influence Air Pollution

Nitric oxide, or NO, is particularly interesting because once it enters the atmosphere it can participate in reactions involved in ozone formation.

Vehicles and combustion sources are major human sources of nitrogen oxides, but soils also produce NO naturally through microbial nitrogen cycling.

Agricultural activity can increase those emissions by supplying large amounts of reactive nitrogen to soil bacteria.

The air chemistry above a fertilized field is therefore influenced partly by reactions occurring underground.

Sunlight and other atmospheric compounds determine what happens after that NO reaches the air.

The bacteria simply begin the chain.

Some Soil Bacteria Remove Methane From the Air

Bacteria do not always add greenhouse gases to the atmosphere.

Some remove them.

Specialized bacteria called methanotrophs can use methane as an energy and carbon source.

Well-aerated forest, grassland, and other upland soils can therefore act as biological sinks for atmospheric methane.

Some methanotrophic bacteria are able to consume methane even at the extremely low concentrations found in ordinary air.

This is an important distinction in a bacterial decomposer story.

Much of the methane produced in oxygen-poor wetlands is generated by archaea, not bacteria. Methane-consuming bacteria can then intercept part of that gas where methane encounters oxygen near the soil surface or around plant roots.

The soil microbiome can therefore contain organisms helping generate methane precursors alongside bacteria that prevent some methane from ever reaching the atmosphere.

Bacteria Can Live on Atmospheric Trace Gases

Methane is not the only atmospheric gas bacteria consume.

Researchers have discovered that many soil bacteria can obtain energy by oxidizing extremely small concentrations of hydrogen and carbon monoxide from the surrounding air.

Some bacteria can survive periods of starvation partly by using these atmospheric trace gases as backup energy sources.

That creates an unusual two-way relationship.

We normally imagine soil organisms releasing gases upward.

In reality, gases also move downward from the atmosphere and become microbial food.

Soil is not merely an emission surface. It is a living chemical filter.

Bacteria Produce Their Own Volatile Chemicals

Anyone familiar with the smell of freshly disturbed soil has encountered microbial chemistry.

Soil bacteria can produce numerous volatile organic compounds, or VOCs.

One famous example is geosmin, a compound associated with the earthy smell of soil after rain and produced by bacteria including Streptomyces.

Bacterial VOCs can serve as chemical signals.

They may attract small soil animals, inhibit competing microorganisms, influence plant growth, or communicate information between organisms separated by soil particles.

Some bacterial volatiles contain sulfur, while others belong to alcohols, ketones, terpenes, and numerous other chemical groups.

Scientists are increasingly studying how these compounds move through soil and whether they meaningfully contribute to the larger pool of biogenic VOCs entering the atmosphere.

Their global atmospheric significance is still much less certain than that of CO₂ or N₂O.

Rain Can Wake the Soil

One of the most dramatic examples of soil-atmosphere interaction occurs after rainfall.

Dry soil can contain bacteria in dormant or slow-growing states.

When water suddenly returns, microbial metabolism accelerates.

Organic compounds become easier to transport through the soil, cells resume activity, and pulses of carbon dioxide and nitrogen gases can follow.

These brief periods of intense microbial emissions are sometimes called hot moments.

For nitrous oxide in particular, rain following dry conditions can trigger disproportionately large emissions because moisture, available nitrogen, and changing oxygen conditions suddenly align.

The atmosphere above a landscape can therefore respond to microbial activity within hours of a weather event.

The Soil Is Part of the Atmosphere

Soil may appear to form a clear boundary between Earth and air.

Chemically, that boundary is extremely porous.

Oxygen moves downward.

Carbon dioxide moves upward.

Methane can move in either direction depending on the microbial community.

Nitrogen compounds are converted between solid, dissolved, and gaseous forms.

Volatile molecules produced by bacteria diffuse through microscopic pores and interact with plants, animals, and eventually the atmosphere.

Soil bacteria are therefore more than decomposers.

They are chemical engineers operating at microscopic scales, continuously deciding—through metabolism—which elements remain underground and which return to the air.

In the next layer of the decomposer story, fungi will add another enormous biological network to that process.

But even without them, bacteria alone make the ground beneath our feet one of the most active chemical interfaces on Earth.

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