Exploring Spatial and Temporal Variations in Stem-Mediated Greenhouse Gas Emissions from Different Species of Mangroves.

Greenhouse gas (GHG) emissions, particularly methane (CH4) and nitrous oxide (N2O), 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 CO2, CH4, and N2O at the stem-atmosphere interface, with A. marina exhibiting the highest GHG fluxes. Notably, stem N2O emissions from A. marina significantly contributed (1.2 to 100.1%) to total ecosystem fluxes, whereas stem CH4 emissions were relatively low (-3.8 to 2.6%). This study is the first to demonstrate seasonal variations in stem N2O flux in mangroves, mainly influenced by temperature, as shown by the structural equation model. The results indicate that stem CH4 and N2O 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 CH4 year-1 and 8.66 [2.46-36.19] Mg N2O 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.