Abstract

Greenhouse gas (GHG) emissions, particularly methane (CH<inf>4</inf>) and nitrous oxide (N<inf>2</inf>O), from mangroves can challenge their carbon sequestration capacity. This study measured GHG emissions from the tree stems of four mangrove species (Avicennia marina, Kandelia obovata, Lumnitzera racemosa, and Rhizophora stylosa) along the western coast of Taiwan. All studied species emitted CO<inf>2</inf>, CH<inf>4</inf>, and N<inf>2</inf>O at the stem–atmosphere interface, with A. marina exhibiting the highest GHG fluxes. Notably, stem N<inf>2</inf>O emissions from A. marina significantly contributed (1.2 to 100.1%) to total ecosystem fluxes, whereas stem CH<inf>4</inf> emissions were relatively low (−3.8 to 2.6%). This study is the first to demonstrate seasonal variations in stem N<inf>2</inf>O flux in mangroves, mainly influenced by temperature, as shown by the structural equation model. The results indicate that stem CH<inf>4</inf> and N<inf>2</inf>O emissions can significantly offset soil carbon burial rates (0.19 to 889.28%), particularly in A. marina. First-order estimates suggest global mangrove stem-mediated emissions of 5.94 [0.88–168.65] Mg CH<inf>4</inf> year^–1 and 8.66 [2.46–36.19] Mg N<inf>2</inf>O year^–1, presented as median [Q1–Q3] values, although these estimates carry some uncertainties. Nonetheless, these insights underscore the importance of including stem emissions in carbon budget assessments for mangrove ecosystems, highlighting their essential role in mitigating climate change.