Chinese Researchers Reveal Mangrove Tree Stems as Major, Overlooked Methane Source
- MM24 News Desk
- 2 days ago
- 3 min read
Scientists from the South China Botanical Garden have discovered that methane emissions from mangrove tree stems are a globally significant phenomenon, offsetting nearly 17% of the carbon these "blue carbon" ecosystems bury annually.
This finding, published in Nature Geoscience, challenges the traditional accounting of mangroves' climate benefits and reveals a substantial previously unquantified source of the potent greenhouse gas.
Mangrove forests are celebrated as climate heroes, efficiently sucking carbon dioxide out of the atmosphere and storing it in their water-logged soils for millennia. However, this "blue carbon" story has a complicating chapter: these same wet, oxygen-poor soils are also a breeding ground for methane.
While emissions from mud and water were known, the role of the trees themselves was a major blind spot. A team led by researchers at the South China Botanical Garden of the Chinese Academy of Sciences set out to close that gap with the first global assessment of the problem.
The research team, whose work was published on November 14 in the journal Nature Geoscience, didn't rely on a single method. They combined years of on-the-ground monitoring at mangrove sites across China with a sweeping analysis of existing global data and sophisticated machine learning models. This multi-pronged approach allowed them to pinpoint what drives these emissions and, crucially, to calculate their global impact.
What they found was striking. The trees themselves are acting as chimneys, channeling methane from the soil into the atmosphere. The study confirmed that methane produced by microbes in the anaerobic soils is transported upwards through specialized tissues in the trees called aerenchyma, which normally help roots get oxygen. The researchers observed a clear gradient, with the highest emissions occurring at the base of the stems and steadily decreasing with height, a pattern strongly supported by isotopic analysis, reported Nature Geoscience.
So, how big is this "tree chimney" effect on a planetary scale? The numbers are sobering. The study estimates that mangrove tree stems release approximately 730.6 gigagrams (Gg) of methane into the atmosphere every year. To put that into perspective, this single pathway offsets about 16.9% of the carbon that mangrove sediments bury each year—a process central to their blue carbon status.
"This work fundamentally changes how we view the mangrove carbon budget," explained a researcher involved with the study. "We can no longer just look at the soil; we have to look at the entire system, and the trees are playing an active and significant role in greenhouse gas exchange."
When these newly quantified stem emissions are added to the known methane releases from the soil, the total methane loss from mangrove ecosystems could offset up to 27.5% of their blue carbon sequestration capacity. This means that assessments focusing solely on carbon burial are likely substantially overestimating the net climate mitigation benefit of protecting and restoring these vital coastal ecosystems.
The implications for global climate policy and carbon accounting are significant. Blue carbon projects, which often finance mangrove conservation through carbon credits, may need to adopt more comprehensive models that include these stem methane fluxes to accurately represent their true climate impact.
This research, supported by the National Natural Science Foundation of China and the National Key R&D Program of China, provides the critical data needed to make those adjustments, ensuring that the value placed on mangroves reflects the full complexity of their interaction with our climate.
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