Land conversion impacts on soil and above-ground microbial nitrous oxide consumption in tropical peatlands

Abstract As tropical peatlands in Southeast Asia are increasingly drained for agriculture, the net effect of this conversion on nitrous oxide (N 2 O) emissions remains unclear. We examined how this land-use change affects nitrogen (N) cycling by comparing two contrasting tropical peat ecosystems in Sarawak, Malaysia: a managed oil palm plantation and a pristine peat swamp forest. We measured soil N 2 O and dinitrogen (N 2 ) emissions, and for microbial functional and structural community and diversity, we quantified the abundances of N cycle functional genes and conducted metagenomic sequencing of microbial communities from below-ground (peat soil and litter) and above-ground (canopy soil and tree leaves) ecosystem compartments. The oil palm plantation soil was a significant N 2 O emitter (65.48 ± 43.18 μg N m −2 h −1 ), whereas the peat swamp soil acted as a near-complete N 2 O sink (0.89 ± 1.18 μg N m −2 h −1 ). Soil microbial communities played a central role in N transformations, with the genus Roseiarcus being the strongest predictor of soil N 2 O emissions, and Paludisphaera most strongly linked to soil N 2 O sink capacity. Oil palm leaves harboured approximately 89% of ammonia-oxidizing bacteria (AOB) per hectare relative to other studied ecosystem compartments (soil and canopy soil) within the oil palm plantation. High N 2 O consumption potential by tropical tree leaves ( Shorea albida and Combretocarpus rotundatus ) indicated that the above-ground compartments contribute substantially—up to two-thirds—to N 2 O uptake in peat swamp forests, as estimated using a scaling approach based on microbial functional gene abundances. Land-use change replaces diverse plant species communities with monoculture oil palm plantations, eliminating specific tree species and their associated soil-leaf-microbe interactions that affect N 2 O emissions and climate effects.