Multi-pathway methane and nitrous oxide emissions from Acacia plantations on tropical peatlands

Tropical ecosystems are major contributors to global methane (CH₄) emissions, yet substantial uncertainties remain in both top-down and bottom-up estimates. Such uncertainties partly can be attributed to limited understanding of various emissions and uptake pathways in tropical ecosystem. Most field measurement of CH4 focused solely on soil-atmosphere exchange, overlooking other exchange pathways. Furthermore, several studies from natural forest ecosystem confirmed significant CH4 emission from tree stems. However, such quantification remains scarce in tropical forest plantations, which constitute significant proportion of current land use. A better quantitative and process-based understanding of CH4 emissions, removals, and transport pathways is therefore essential for improving regional and global CH4 budgets and mitigation strategies, especially under changing climate and land use.In this study, we measured soil and stem CH4 fluxes from two managed plantation forests (Acacia and Eucalyptus plantations) and two natural forests ecosystem (peat swamp forests and riparian forests) in Sumatra, Indonesia. We used LI-8200-01S (LICOR, USA) for soil and semi-rigid chambers made with polyethylene terephthalate (PET) plastic sheets for stem measurements. We used LI-7810 (LICOR, USA), connected to the chambers during the measurement period to measure the CH4 concentration. The fluxes were calculated using a linear function of changes in CH4 concentration during incubation time.The preliminary result shows that plantation emits significantly smaller CH4 from both soil and stem compared to respective natural forested ecosystems, indicating that land-use change substantially alter the methane production, consumption, and transport processes. We observed a clear decreasing stem CH4 fluxes with increasing stem height in both ecosystems on peat, strongly suggest a soil-originated CH4 transport mechanism. Interestingly, no significant difference between stem height was detected in Eucalyptus plantations and adjacent riparian forests. Tree stems acted as net CH4 sources across all ecosystems. Soil surfaces functioned as CH4 sources in peatland ecosystems but as net CH4 sinks in Eucalyptus plantations and adjacent riparian forests. These results demonstrate strong contrasts in soil–stem CH4 dynamics between peatland and non-peatland ecosystems in tropics. Comprehensive, pathway-specific assessments are therefore required to reduce uncertainties in tropical CH4 budgets.