Mangrove forests are often regarded as climate heroes that absorb and store carbon dioxide along coastlines more efficiently than most terrestrial forests. These “blue carbon” ecosystems bury organic carbon deep in their sediments, serving as powerful natural sinks that help mitigate global warming. Yet, the more we studied these unique tidal forests, the more we began to wonder whether the story was really so simple. Could these carbon-storing ecosystems also be quietly releasing greenhouse gases back into the atmosphere?
That question set the foundation for our recent research, published as “Mangrove sediment carbon burial offset by methane emissions from mangrove tree stems.” Methane (CH4) is a potent greenhouse gas with a global warming potential dozens of times higher than that of CO2. While scientists have long known that mangrove soils can produce methane, very few considered that the trees themselves might act as release pathways. Our work reveals that mangrove stems can emit substantial amounts of methane, enough to offset up to 16.9% of the carbon that these ecosystems bury annually. This finding reshapes how we view the net climate role of mangroves, showing that they are not just carbon sinks but dynamic systems where both storage and leakage occur simultaneously.
Our journey began deep in the muddy mangroves of southern China. During early field surveys, we noticed unusually high methane concentrations around the roots of certain tree species. Out of curiosity, we placed small chambers directly on the stems to test whether gas was escaping through the bark. To our surprise, the instruments detected clear and consistent methane emissions from the stems themselves. That discovery led us to design a series of in situ measurements at multiple mangrove sites across China. We used gas analyzers to measure methane fluxes from soils, leaves, and stems. The results were striking. Tree stems released far more methane than any other part of the ecosystem, especially near the base, pointing to a strong upward movement of methane from the soil to the atmosphere through the plant.
Once we completed the local observation, we sought to understand its global impact. To do so, we compiled over 1,700 observations from both our fieldwork and published datasets, covering mangrove forests from Asia to South America. We used machine learning models to explore how factors like soil temperature, salinity, and wood traits affect methane fluxes. The model revealed that warm, humid regions with high soil carbon content tended to have stronger stem emissions. By integrating these relationships with global mangrove distribution data, we estimated methane release at the global scale and compared it to mangrove carbon burial rates. The outcome was both fascinating and humbling: the very trees responsible for it were also releasing a portion of that stored benefit back into the atmosphere as methane—a smaller but significant trade-off.
Behind these data lies the story of perseverance. Conducting precise gas flux measurements in mangrove forests is a challenge few outside the field can imagine. Each day meant trudging through thick mud under the tropical sun, synchronizing sampling with the tides, and protecting fragile instruments from saltwater. Despite these challenges, each successful measurement felt like a small victory that revealed an invisible process linking the soil, the trees, and the atmosphere in one continuous breath.
The discovery that mangrove stems can serve as major methane pathways challenges the traditional narrative of blue carbon ecosystems. It does not diminish their value but rather makes our understanding more complete. For climate models and carbon accounting, these findings underscore the need to consider methane emissions alongside carbon burial to obtain a true picture of mangrove contributions to the global carbon budget. More broadly, it reminds us that nature’s balance sheets are complex, and every ecosystem that stores carbon may also release it in another form.
Looking ahead, we hope to explore how tree traits, microbial activity, and environmental changes jointly regulate methane transport in mangroves. Could certain species or restoration strategies minimize methane leakage while maximizing carbon sequestration? Can we harness microbial processes to enhance methane oxidation inside stems? These are the questions guiding our next steps.
In the end, this research taught us that mangrove forests breathe in more ways than one. They inhale carbon dioxide and exhale methane, a dual process that reflects the intricate balance of life in coastal ecosystems. Understanding both sides of this exchange will help us protect mangroves not just as carbon stores, but as living systems whose complex rhythms shape the climate of our planet.