Soil and tree stem greenhouse gas fluxes from nutrient-rich and nutrient-poor tropical peatland forests

Tropical peatland forests are significant sources and sinks of greenhouse gases (GHG), yet the relative contributions of soil and tree stem fluxes have remained poorly quantified, particularly CH₄ and N₂O fluxes across gradients of nutrient availability. We conducted simultaneous measurements of CO₂, CH₄ and N₂O fluxes from both soil and tree stems using soil and stem chamber in two contrasting tropical peat swamp forests: a nutrient-rich in Quistococha, Peru and a nutrient-poor in Maludam, Sarawak, Malaysia. Our results showed higher soil CO₂, CH₄ and N₂O fluxes from Quistococha nutrient-rich forest. Tree stem respiration was consistently higher in the nutrient-poor forest across all dominant species in both forests. Tree stem CH₄ fluxes exhibited distinct patterns, with significantly higher emissions from the nutrient-rich forest, while displaying species-specific behaviour among dominant tree species. Mauritia flexuosa palm stems in Quistococha showed high emission of CH₄ from stems with potential CH₄ sinks from specific species from both forests. N₂O emissions were also species-specific and higher from the nutrient-rich forest, with negligible fluxes observed from the species in the nutrient-poor forest. From stem fluxes to tree fluxes upscaling, we found that the majority of total ecosystem GHG flux originated from soil with minimal contribution from the dominant tree species. In conclusion, these findings highlighted tree stems from tropical peatland can act as sources and sinks and that nutrient availability influence on the magnitude of greenhouse gas emissions.