Isotopic evidence for axial tree stem methane oxidation within subtropical lowland forests

Knowledge regarding mechanisms moderating methane (CH4) sink/source behaviour along the soil–tree stem–atmosphere continuum remains incomplete. Here, we applied stable isotope analysis (?13C-CH4) to gain insights into axial CH4 transport and oxidation in two globally distributed subtropical lowland species (Melaleuca quinquenervia Casuarina glauca). We found consistent trends flux (decreasing with height) ?13C-CH4 enrichment (increasing relation stem height from ground. The average lower tree (0–40 cm) of Melaleuca (?53.96‰ ?65.89‰) were similar adjacent flooded soil ebullition (?52.87‰ ?62.98‰), suggesting that is derived mainly by sources. Upper stems (81–200 displayed distinct ?44.6‰ ?46.5‰, respectively). Coupled 3D-photogrammetry novel 3D-stem measurements revealed hotspots isotopic fractionation on Melaleuca, which likely due bark anomalies preferential pathways gas efflux enhanced. Diel experiments greater higher rates afternoon, compared morning. Overall, estimated c. 33% was oxidised between upper during transport, therefore potentially representing a significant, yet previously unaccounted for, sink.