Allowing the soil to breathe more freely

The hidden life beneath our feet

A single gram of soil can contain a billion bacteria. Together with fungi and other microorganisms in the soil, these bacteria decompose dead plant parts, animal remains, and root exudates – the fluids emitted through the roots of plants. This metabolizing of the dead organic material and releases CO₂. This process, known as soil respiration, is a central component of the global carbon cycle. But how exactly does this CO₂ release occur? And what influences it? Until now, the number of microorganisms (or microbes for short) was considered the decisive factor. More microbes, more respiration – that was the equation. “It has always been assumed that microbes in the soil multiply very quickly, even exponentially, under certain conditions,” explains microbiologist Magdalena Nagler. “This was thought to determine higher soil respiration, in other words, more CO₂ being released from the soil.” However, Nagler's study shows that this assumption falls short. The decisive factor is how active the microbes actually are.

Counting cells is not enough

In an experiment on alpine meadows in South Tyrol, Nagler combined CO₂ measurements with genetic analyses of soil microbes. She specifically isolated DNA from intact, living cells to ensure that she did not accidentally count the DNA of dead organisms – a common pitfall in previous research. “The problem is that DNA can still be present even if the microorganism is no longer there,” explains Nagler. “When a microorganism dies, it disintegrates, and its DNA is released. It is then no longer inside a cell, but remains in the soil, where it can survive for a long time.” Nagler removed this extracellular part of the environmental DNA from the soil samples and examined only the intracellular DNA of the microbes. The result: even with similar numbers of microbes, the measured CO₂ values differed significantly depending on how active the microbes were. Nagler used this data to calculate a “gene-specific respiration rate” – how much CO₂ is released per specific gene segment. And it was precisely this value that proved to be decisive.

Dormancy and awakening

What Nagler was able to show in her research was that microbes in the soil fall into a state called dormancy for short periods of time. They are present but when “sleeping” demonstrate little metabolic activity if conditions are unfavorable. As soon as sufficient moisture, warmth, and sunlight are available, they “awaken,” become active, and begin to breathe. What is striking is that sites with steep slopes showed significantly higher microbial activity than flat meadows. This is due to stronger solar radiation. Factors such as the pH value or the carbon-nitrogen ratio in the soil also influenced respiration – not by changing the types of microbes, but by changing the levels of activity within the same community.

Basis for improved climate models

The study not only represents a methodological advance, its findings are also important for better understanding the effects of climate change on carbon fluxes in the soils of mountainous areas – where there are many different microclimatic conditions within very small areas. Due to this particularity, it can be challenging for researchers to develop large-scale climate models. However, by including microbial dynamics, predictions of soil carbon emissions can be improved and the effects of global warming on soils and ecosystems be better assessed. Specifically, how dry periods or heat waves affect CO₂ emissions. Nagler’s experiment also revealed thar even short bursts of moisture, such as after rain, led to sudden CO₂ emissions: a phenomenon known as the Birch Effect. Thanks to the study, the occurrence can now be better understood.

Conclusion: Activity is crucial

Magdalena Nagler’s study brings a new and previously underestimated perspective to soil research: it is not only the number of microbes present that counts for CO₂ release, but above all how active they actually are. If we understand what triggers the switch between dormancy and activity in microbes, we will also better understand how soils respond to climate change. So, should we slow down microbial activity to reduce emissions? “We definitely should not begin by inhibiting soil respiration to reduce CO2. Soil respiration is useful; it is a sign of healthy soil and is crucial for the growth of plants and trees – the basis of our food,” explains Nagler.