Mangrove stem methane emissions significantly offset global blue carbon sequestration

This is the authors' abstract. We don't add key points for this paper.

Wetlands, including mangrove forests, are major contributors to global methane (CH4) emissions, a potent greenhouse gas. Recent evidence suggests that CH4 emissions from tree stems may play a significant role in the global carbon budget. This study investigated stem CH4 emissions in mangroves. We find that stem CH4 emissions are greatly neglected in mangroves, and can significantly offset their blue carbon function. The stem CH4 flux rates are well correlated with wood density and wood water content, with lower wood density and higher wood water content facilitating higher emissions. Additionally, stem CH4 emissions are influenced by hydrological conditions, with higher emissions observed under high tidal levels. It is worth noting that the majority of stem CH4 emissions originate from the soil, as evidenced by the strong correlation between stem CH4 emissions and soil CH4 flux. Based on literature synthesis and data integration, we extrapolate our findings and estimate that mangrove stem CH4 emissions on a global scale amount to approximately 0.31 Tg yr-1. This highlights the potential of stem CH4 emissions to partially offset blue carbon burial rates in mangroves, with an average offset of 15.2%. These findings emphasize the importance of incorporating stem CH4 emissions into future blue carbon budgets for mangroves.