Changing Vegetation in Thawing Permafrost Increases Emissions of Greenhouse Gases

Changing vegetation in thawing permafrost increases emissions of greenhouse gases

March 26, 2026
by Christfried Dornis, University of Tübingen

Research indicates that the plant communities emerging on thawing permafrost in the Arctic are evolving, with grasses increasingly replacing slower-growing shrubs. Despite the ability of these grasses to sequester more carbon dioxide than their predecessors, they are associated with significantly higher methane emissions throughout the year. Methane, a potent greenhouse gas, exacerbates global warming at a rate considerably faster than carbon dioxide.

A collaborative team from the University of Tübingen has extensively examined the relationship between vegetation and greenhouse gas emissions within both wet and damp soils. Their primary aim was to accurately measure the impact of various plant species on greenhouse gas emissions over different seasons in the thawing permafrost peatland located in Stordalen, near Abisko, Sweden. Led by Professor Marie Muehe, affiliated with both the University of Tübingen and the Helmholtz Centre for Environmental Research in Leipzig, alongside Professor Andreas Kappler from the University of Tübingen, the findings have been published in the journal Global Change Biology.

Muehe elaborates on the changes occurring, stating, "The typical peat palsas of Stordalen mire are comparatively dry. They lie atop the permafrost, which has historically allowed water drainage over the underlying ice sheet. However, as this ice begins to melt, the drainage patterns are altered. Consequently, the peat palsas transition into bogs and ultimately into fens."

In this increasingly saturated environment, slow-growing, permafrost-adapted shrubs such as bog rosemary and dwarf birch trees struggle to thrive. Although Sphagnum mosses initially establish themselves, they too are ultimately supplanted by faster-growing grass species like cotton grass and sedge as the ice layer continues to melt and the soil becomes increasingly waterlogged.

Through the process of photosynthesis, green plants absorb carbon dioxide from the atmosphere, converting it into organic compounds that support their growth. Marie Mollenkopf, a Ph.D. student working with Muehe and Kappler and the lead author of the study, explains, "Some of these organic substances, including sugars and amino acids, are naturally exuded by the plant through their roots into the soil, providing energy sources for microbial growth."

The type of microbial populations that thrive in the root zones of these plants is influenced by a variety of factors, such as nutrient availability and oxygen levels. "This creates complex food webs, where certain microbes utilize the compounds released by the plants, while others may feed on the byproducts of the first group. Ultimately, varying quantities of greenhouse gases, including carbon dioxide and methane, are released into the atmosphere," Mollenkopf adds.

To obtain their data, the research team systematically recorded the carbon fluxes within the root zones of different plant communities throughout Stordalen mire. They conducted measurements at predetermined intervals during the growing season, focusing on both the natural root exudates and the greenhouse gas emissions produced. Environmental conditions related to soil chemistry were also incorporated into the study. The research involved a comparative analysis across three distinct thaw stages: the original palsas, the bog, and the fens.

The results indicated that grasses primarily drive the seasonal dynamics of carbon fluxes and greenhouse gas emissions in both thawed bogs and fens. As thawing continues, these grasses not only release more carbon but also actively increase methane emissions. Mollenkopf notes, "From early to late summer, particularly between June and August, grasses sequestered substantial amounts of carbon dioxide—far exceeding what was captured by peat bogs or shrubs. However, as the season progressed, methane emissions from these grasses peaked in late summer. In aggregate, the emissions of methane outweighed the beneficial carbon dioxide absorption. Additionally, autumn saw increased CO2 release due to diminished photosynthesis and decaying plant matter, which amplified overall greenhouse gas emissions ninefold."

Muehe highlights the implications of these findings: "As permafrost thaws, it typically shifts from being a carbon sink to a carbon source, with grasses significantly contributing to carbon release at the close of the growing season."

"Permafrost soils sequester nearly half of the carbon present in global soil reserves. Plants can expedite the transition of thawing permafrost regions from carbon sinks to sources by altering soil processes throughout the year, which is happening more rapidly and dramatically than previously understood. Global climate models must incorporate not only the permafrost itself but also the dynamic plant interactions occurring within these ecosystems," asserts Mollenkopf.

Professor Dr. Karla Pollmann, president of the University of Tübingen, concludes, "The findings from Stordalen underline the necessity of comprehensively understanding climate change to effectively mitigate its impacts. We can achieve this through precise knowledge of the processes at play in sensitive ecosystems like permafrost regions. The University of Tübingen's research offers valuable insights into the significant role of soils in the global carbon cycle, which is critical for informed climate and environmental policy."