Of Microbes and Mires: What the Diet of Bacteria Has to Do with the Global Climate

What comes to mind when you hear the word “mire”? A foggy moor from an Agatha Christie novel? The squelch of rubber boots in wet ground? Mires and peat bogs can be found in many places around the world, including Russia, Brazil, Indonesia and Canada. Europe alone has around 59 million hectares of them. 

These soggy landscapes are not just an atmospheric scenery for novels, they are ecological “overachievers". They host rare birds, plants, and insects, they cool their surroundings, filter out excess fertilisers and can buffer floods. Much of this magic is thanks to humble peat mosses. Not only do they squeak under rubber boots, they can also store 20 times their own weight in water.

And they are climate heroes, too. Over millennia, plant remains have been compressed into peat, locking away carbon. Today, peatlands store an estimated 550 billion tons of carbon - twice as much as all the world’s forests combined.

But human intervention has disrupted this balance. Peatlands are natural carbon vaults - but only as long as they stay wet. Once drained, they stop storing carbon and start releasing it. And that shift has global consequences.

Today, about 12% of the world’s peatlands have been drained or degraded. Instead of locking away carbon, they now emit around 2 billion tons of CO₂ equivalents every year or roughly 4% of all global greenhouse gas emissions. That's more than the annual emissions of the entire commercial aviation industry.  In the European Union, the picture is just as stark. Drained peatlands are responsible for 5% of the EU’s total emissions - equivalent to a quarter of all industrial emissions across the bloc.

And it’s not just wild peat bogs. About 2.5% of EU land is made up of former peatlands now used for conventional farming, roughly one in ten cropland hectares. These fields are vital for farmers, but they also release 144 megatons of CO₂ equivalents every year - twice as much as the entire country of Austria.

“Various microbial communities live in peatland soils and mires,” explains microbiologist and ECH member Petra Pjevac. “Some of these single-cell microorganisms, such as bacteria and archaea, thrive in oxygen-poor conditions found in wet mires. Others need oxygen-rich conditions.” In wet peatlands, oxygen is scarce, slowing microbial activity and keeping carbon locked in the soil. But when peatlands are drained, oxygen rushes in. Microbes feast on carbon and release CO₂. Fertilizers add to the problem. They stimulate nitrification processes. These convert ammonia into the potent greenhouse gas nitrous oxide (N₂O), which enters the air, and into nitrate, which enters the groundwater. Ammonium ions can be absorbed to peat and stored for a certain period. However, when oxidized to nitrate, it can easily be washed out and contributes to groundwater pollution.

The takeaway: If we want peatlands to help combat climate change, we must keep them wet - or rewet them. The best thing is: Peatlands don't have to be either wild or wasted. In fact, they can be both productive and intact.

Through a practice known as paludiculture, farmers are cultivating plants that naturally thrive in saturated soils - like reeds, cattails, sedges, alders, and even berries - for use as biomass, building materials, or food. “Reeds, cattails and sedges are the most important products in fens, a type of mire connected to groundwater,” explains geoecologist Stephan Glatzel of the Environment and Climate Research Hub. “Trees like alders can also be cultivated - trials are already underway.” 

But can wet farming really deliver climate benefits? That is what Glatzel and biogeochemist Kyle Boodoo set out to test in the international PRINCESS project. They studied greenhouse gas emissions from 14 re-wetted peatland sites across Germany, the Netherlands, and Poland - each a former pasture or cropland, once heavily fertilized. The team compared emissions from sites under different levels of paludiculture - ranging from low to high harvest intensity - with those left untouched as “wet wilderness.”

The results were striking. “Our findings show that there is no difference in total greenhouse gas emissions between re-wetted sites and those under high or low-intensity paludiculture,” says Boodoo. “That means we can use re-wetted peatlands productively and still get the climate benefits of peat rewetting.”

In other words: farming doesn’t have to drain the land - or the climate.

To better understand how land use affects carbon dynamics in peatlands and why paludiculture could be the solution, biogeochemist Kyle Boodoo teamed up with microbiologist Petra Pjevac to launch a seed-funding project at the Environment and Climate Research Hub. Their goal: to explore how carbon quantity and quality vary across different land uses - including paludiculture - and how this shapes microbial communities that feed on carbon.

They are also examining how factors such as groundwater levels, temperature and nutrient availability influence microbial processes and, ultimately, the release of greenhouse gases. It turns out that the chemistry of the soil is closely tied to the microbial communities that inhabit it. As it turns out, microbial metabolism plays a big part in Peatlands and their Carbon Footprint. In drained or recently re-wetted peatlands, microbes encounter simpler, more digestible carbon compounds - fuel for aerobic respiration, which releases CO₂.

“More CO₂ and nitrous oxide is released from degraded peatlands which have been drained or only recently re-wetted,” Boodoo explains. “This is because microbes have the oxygen and warmer temperatures to carry out aerobic respiration of the carbon in peatlands. Under long-term flooded conditions, the oxygen is used up and CO₂ release halts.”

In drained sites, microbial activity accelerates decomposition, producing both complex, hard-to-break-down compounds and fresh, easily degradable ones. Environmental conditions amplify this effect. “Higher temperatures and oxygen levels in drained sites increase the potential for microbes to convert organic material into CO₂,” says Boodoo. “That contributes to greenhouse gas emissions and climate warming.”

But paludiculture seems to change the equation. “It is clear that there is less available and easily degradable carbon in paludiculture,” Boodoo notes. “Microbes are less able to break it down. This is fantastic news.”

Early results suggest that more frequent harvesting may even enhance carbon storage. And the type of crop - reeds versus sedges, for instance - can influence how much carbon is stored and how accessible it is to microbes.

Through their international and interdisciplinary work, ECH researchers are uncovering how re-wetted landscapes function – microbe by microbe, molecule by molecule. So next time you think of mires, consider not just the mud, but also the dietary preferences of their tiniest residents.