The research, led by Alberto Borges, an oceanographer and head of the CO2 Lab at the University of Liège, represents the largest investigation of its kind ever conducted. The team carried out 503 individual measurements spanning lakes that range from oligotrophic systems with very low algal biomass and strikingly clear waters to hypereutrophic lakes whose waters are rendered green by dense blooms of phytoplankton, the community of microscopic algae suspended in the water column. This extraordinary gradient of lake types allowed the researchers to test, at continental scale, what actually controls the fate of methane once it is produced in lake sediments and diffuses upward through the water.

To understand why this finding matters, it helps to consider the underlying chemistry and microbiology of methane in freshwater systems. Methane emissions from a lake, as Borges explains, are the result of a balance between two opposing processes. On the production side, methanogenesis occurs in the oxygen-free sediments at the bottom of the lake, where archaeal microorganisms decompose organic matter and release methane as a metabolic byproduct. On the loss side, microbial oxidation takes place in the water column, where a specialized group of bacteria known as methanotrophs consume methane as their preferred substrate, using it both as a source of energy and as the raw material for building their own biomass. The net emission that reaches the atmosphere is simply what remains after this microbial consumption has had its effect.

The central discovery of the new study is that methane oxidation increases sharply with the amount of microalgae present in the water. The surfaces of these algae are colonized by communities of bacteria, and among them are methanotrophs that exist in a mutually beneficial relationship with their algal hosts. The methanotrophs supply the algae with carbon dioxide, which the algae use for photosynthesis, while the algae in turn produce the oxygen that the bacteria require to oxidize methane. This tight metabolic coupling means that the more abundant the microalgae become, the more abundant the methanotrophic bacteria become as well, and the more intense the oxidation of methane turns out to be. In the most productive lakes studied, oxidation rates reached levels tens of thousands of times higher than those measured in the poorest lakes.

The scale of this consumption is far from trivial. According to the study, oxidation is the main fate of methane dissolved in the surface waters of the lakes examined, eliminating more than 70 percent of it. That is substantially more methane than ultimately escapes into the atmosphere, which means that without this bacterial activity, lake emissions would be considerably higher than current estimates suggest. The finding reframes the way scientists think about the greenhouse gas budget of inland waters, because a process that was often treated as a secondary detail in methane cycling turns out to be the dominant control on how much methane actually reaches the air.

The study also uncovered a second, geographically distinct source of intense methane oxidation. Lakes bordered by the flooded forests of the Congo Basin were characterized by particularly high levels of oxidation, fueled by an influx of bacteria originating from the submerged forest soils. This suggests that the connection between terrestrial ecosystems and lake methane dynamics extends beyond the simple delivery of organic carbon. Flooded forests appear to seed adjacent waters with methanotrophic communities, adding another layer of biological control to the methane budget of these tropical systems and highlighting the importance of riparian and wetland vegetation in regulating greenhouse gas fluxes.

What makes the result especially consequential is how it interacts with the ongoing global problem of eutrophication, the enrichment of waters with nutrients that drives excessive algal growth. Earlier work by the same team had shown that as phytoplankton biomass increases, methane production in the sediments increases as well, because algal detritus sinking to the lake bottom serves as a rich feedstock for the methane-producing microorganisms living there. On its own, that relationship painted a worrying picture: the greener and more polluted a lake becomes, the more methane it should emit. The new study demonstrates that the reality is more nuanced, because two opposing effects occur simultaneously in eutrophic waters.

As pollution drives phytoplankton to proliferate, methane production in the sediments rises, but the methanotrophic bacteria attached to the algae multiply in parallel and consume an increasing share of that methane. Crucially, in the lakes studied, the increase in oxidation can outweigh the increase in production. In the absence of these algae-associated bacteria, methane emissions into the atmosphere would be much higher than what is actually observed. The bacteria therefore act, in Borges’s words, as natural and welcome filters that partially mitigate the effect of lake pollution on global warming. It is an important piece of the puzzle that was missing, and one that will allow researchers to better predict the future trajectory of methane emissions from lakes as eutrophication continues to spread across the tropics and beyond.

The implications extend well beyond African lakes. Tropical and subtropical freshwaters are among the most productive ecosystems on Earth, and many are experiencing accelerating nutrient loading from agriculture, urbanization, and wastewater discharge. If the coupling between phytoplankton and methanotrophs documented here proves to be a general feature of productive lakes, then global methane budgets for inland waters may need to be revised downward, and the models used to project future emissions will need to incorporate algal-bacterial symbiosis as a first-order control rather than a footnote. Conversely, any environmental change that disrupts this symbiosis, such as shifts in nutrient regimes, light availability, or water chemistry, could tip the balance back toward greater emissions.

For now, the study stands as a vivid reminder that the climate system is shaped not only by vast physical processes but also by intimate partnerships between microscopic organisms. On the surface of a single algal cell drifting in a green African lake, a bacterium consumes methane and exhales carbon dioxide that the alga immediately recycles into oxygen and organic matter. Multiplied across hundreds of lakes and billions of microbial encounters, this quiet exchange removes the majority of the methane that would otherwise warm the planet. Understanding and protecting such natural filters may prove to be an essential part of anticipating how freshwater ecosystems will respond to a changing, increasingly nutrient-rich world.

Subject of Research: Methane oxidation by algae-associated methanotrophic bacteria in African lakes

Article Title: In African lakes, microbes living on algae reduce a powerful greenhouse gas

Article References: In African lakes, microbes living on algae reduce a powerful greenhouse gas. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: methane, methanotrophs, microalgae, African lakes, eutrophication, greenhouse gases, phytoplankton, Nature Communications, University of Liège, Congo Basin, biogeochemistry, freshwater emissions

The central puzzle the study addresses is deceptively simple. Aquatic plants are equipped with internal air channels, known as aerenchyma, that shuttle oxygen down to their waterlogged roots while allowing gases produced in the sediment to escape upward and out into the atmosphere. This plumbing system makes plants the primary conduit through which methane, generated by microbes decomposing organic matter in oxygen-starved sediments, reaches the air. But the same root zone also hosts methanotrophic bacteria, methane-consuming microbes that thrive where oxygen leaking from roots meets methane rising from below. The question has always been how much methane these bacteria intercept before it ever enters the plant’s internal gas highway.

Previous measurements of this process, called rhizospheric oxidation, had been carried out on only a handful of species in natural settings, leaving scientists with little idea of how the phenomenon varies across the enormous diversity of aquatic plants. Some species move gases with remarkable efficiency, using pressure-driven convective bulk flow that can ventilate their tissues rapidly, while others rely on slower molecular diffusion. Grasset reasoned that this variation in transport efficiency might hold the key to understanding why some vegetated habitats emit far more methane than others, and she designed an experiment to test the idea across an unusually broad range of species.

The study examined eleven different aquatic plant species spanning a spectrum of gas transport capabilities. To quantify both methane oxidation and methane transport simultaneously and in situ, Grasset employed a dual stable isotope approach, a technique that tracks the fate of methane molecules by measuring how their isotopic signatures shift as they move through the plant-soil system. Because methanotrophic bacteria preferentially consume lighter isotopes of methane, the residual methane that survives oxidation and reaches the atmosphere carries a distinctive heavy isotopic fingerprint. By reading these fingerprints in the field, the researcher could calculate what fraction of the methane produced in the sediment was being oxidized in the rhizosphere of each species before release.

The results were striking. For plants that transport gases efficiently, up to eighty-one percent of the methane produced in the surrounding sediment was oxidized before it could escape through the plant tissues. In other words, in the most effective gas movers, more than four out of every five methane molecules generated by methanogenic archaea in the anoxic sediment never made it to the atmosphere at all. They were instead converted to carbon dioxide by methane-oxidizing bacteria in the thin oxygenated halo surrounding the roots, a transformation that drastically reduces the climate impact of the carbon leaving the sediment.

Perhaps even more consequential was the pattern that emerged across species. The fraction of methane oxidized was negatively correlated with the amount of methane each plant released. Efficient gas transporters, despite their powerful internal ventilation systems that might be expected to flush methane out rapidly, ended up emitting less methane than their slower-breathing counterparts. This counterintuitive relationship suggests that the very plants best equipped to move gases are also the ones that deliver the most oxygen to their rhizospheres, fueling the methanotrophic bacteria that consume the methane before it can be vented. The efficient plumbing, in effect, feeds the biological filter that neutralizes the gas.

Grasset is careful to note that the correlation, while compelling, does not yet establish causality. It remains possible that other factors, such as sediment chemistry, root architecture, or differences in methane production rates among the studied habitats, contribute to the observed pattern. Further experimental studies will be needed to confirm that high gas transport efficiency directly drives higher rhizospheric oxidation. Even so, the magnitude of the oxidation fractions measured, and their consistent relationship with plant-mediated methane release across eleven species, represents a major advance over the sparse species-level data that existed before.

The implications for global climate science are considerable. Methane emissions from vegetated freshwater habitats are among the most uncertain terms in global greenhouse gas budgets, in large part because emission models struggle to account for the enormous variability observed between different plant communities and species. Current approaches often treat aquatic vegetation as a single functional group, or rely on crude proxies for plant-mediated transport. If rhizospheric oxidation varies systematically with species traits such as gas transport efficiency, as this study suggests, then incorporating that trait into emission models could dramatically reduce the uncertainty in methane budgets for wetlands, lake margins, and other vegetated inland waters.

The study also points toward a practical framework for classifying aquatic plants by their climate behavior. Grasset argues that a mechanistic understanding of how plants release methane is necessary to define aquatic plant functional types with contrasting methane emissions, analogous to the plant functional types long used in terrestrial vegetation models. Species with high gas transport efficiency and high rhizospheric oxidation would fall into one category, emitting relatively little methane per unit of production, while species with sluggish internal ventilation and weak oxidation would form another. Mapping which types dominate which ecosystems could allow Earth system models to generate far more accurate predictions of how freshwater methane emissions will respond to climate change, permafrost thaw, and shifting vegetation distributions.

As researchers work to refine these models, the study stands as a vivid reminder that some of the most important climate regulation on the planet happens at scales invisible to the naked eye, in the oxygenated microzone hugging the roots of a water lily or a reed. The dual isotope technique deployed here offers a template for future in situ measurements across other ecosystems and climates, from boreal fens to tropical floodplains. If the relationship between transport efficiency and oxidation holds up under further scrutiny, the humble root zone of aquatic plants may prove to be one of nature’s most underappreciated methane filters, quietly scrubbing the majority of a potent greenhouse gas from the flux that would otherwise escape into a warming atmosphere.

Subject of Research: Methane rhizospheric oxidation by aquatic plants and its role in regulating freshwater methane emissions

Article Title: Methane rhizospheric oxidation and its ecosystem significance across different aquatic plant species

Article References: Grasset, C. (2026). Methane rhizospheric oxidation and its ecosystem significance across different aquatic plant species. Biogeochemistry. https://doi.org/10.1007/s10533-026-01374-4

Image Credits: AI Generated

DOI: 10.1007/s10533-026-01374-4

Keywords: methane, aquatic plants, rhizosphere, methanotrophy, aerenchyma, greenhouse gas, stable isotopes, wetlands, biogeochemistry, plant-mediated transport, freshwater emissions, climate