The study, published in the journal Biogeochemistry by a team led by Laura Kuusemets and Mikk Espenberg of the University of Tartu in Estonia, together with colleagues including Lulie Melling of the Sarawak Tropical Peat Research Institute, compared two contrasting tropical peat ecosystems side by side: a managed oil palm plantation and a pristine peat swamp forest. The researchers measured fluxes of both nitrous oxide and dinitrogen gas from the soil, quantified the abundances of nitrogen cycling functional genes using quantitative PCR, and conducted metagenomic sequencing of microbial communities drawn from multiple ecosystem compartments, both below ground in the peat soil and litter, and above ground in canopy soil and tree leaves.

The headline numbers are striking. The oil palm plantation soil emitted nitrous oxide at a rate of 65.48 micrograms of nitrogen per square meter per hour, on average, with considerable variability, whereas the peat swamp forest soil consumed the gas, registering a flux of just 0.89 micrograms of nitrogen per square meter per hour. In other words, the intact forest soil acted as a near-complete sink for nitrous oxide, while the drained, cultivated plantation soil released it in substantial quantities. Because nitrous oxide is such a powerful greenhouse gas and also the dominant stratospheric ozone-depleting substance, this reversal carries real consequences for regional and global emission budgets.

To understand what drives this flip, the team looked beneath the flux measurements to the microbes themselves. Soil microbial communities, they found, play a central role in the nitrogen transformations occurring in these ecosystems. Two bacterial genera emerged as particularly informative. The genus Roseiarcus was the strongest single predictor of soil nitrous oxide emissions, while Paludisphaera was most strongly linked to the soil’s capacity to consume the gas. These findings suggest that the direction and magnitude of nitrous oxide exchange in tropical peat can be anticipated, at least in part, from the composition of the microbial community, offering a potential biological fingerprint of whether a given peat landscape is likely to emit or absorb the gas.

The research also breaks new ground by extending the analysis above the soil surface. Microbes are not confined to peat; they colonize leaf surfaces, bark, and the canopy in ways that can influence trace gas exchange. In the oil palm plantation, the researchers calculated that oil palm leaves harbored approximately 89 percent of the ammonia-oxidizing bacteria found per hectare across the studied ecosystem compartments of soil and canopy soil. Ammonia-oxidizing bacteria are key players in the nitrogen cycle, involved in pathways that can ultimately generate nitrous oxide, so their dominance on plantation foliage points to an above-ground dimension of nitrogen cycling that is often overlooked in greenhouse gas accounting.

In the pristine peat swamp forest, the above-ground story takes a different and rather remarkable turn. The leaves of two characteristic tree species, Shorea albida and Combretocarpus rotundatus, showed high nitrous oxide consumption potential. Using a scaling approach based on microbial functional gene abundances, the researchers estimated that these above-ground compartments contribute substantially to the forest’s total nitrous oxide uptake, accounting for up to two-thirds of the gas consumed in the peat swamp forest ecosystem. That finding reframes how scientists think about forest-atmosphere exchange: the canopy is not merely a passive surface but an active zone of greenhouse gas processing, mediated by the microbial communities that live on and in the foliage.

The implications of land-use change therefore run deeper than simple soil disturbance. When diverse tropical peat swamp forests are replaced with monoculture oil palm plantations, specific tree species and their associated soil-leaf-microbe interactions are eliminated. The study indicates that these interactions matter for nitrous oxide emissions and their climate effects. A forest in which leaves actively consume nitrous oxide and soils absorb nearly all of what remains behaves very differently from a plantation in which foliage hosts abundant ammonia oxidizers and drained soils vent the gas to the atmosphere. The loss of particular plant species, in other words, appears to dismantle a biological buffering system that intact forests provide.

Methodologically, the study is notable for combining gas flux measurements with molecular tools across the full vertical structure of the ecosystem. Quantitative PCR allowed the team to count copies of nitrogen cycle functional genes in each compartment, providing a proxy for the potential of different microbial groups to produce or consume nitrous oxide. Metagenomic sequencing then gave a broader picture of the structure and diversity of the microbial communities inhabiting peat soil, litter, canopy soil, and leaves. By integrating these data streams, the researchers could link specific taxa and functional capacities to measured gas fluxes, and scale from leaf-level potentials to ecosystem-level estimates of above-ground uptake.

The broader context is the rapid transformation of Southeast Asian peatlands. These waterlogged, organic-rich soils have accumulated carbon over millennia, but drainage for agriculture, particularly oil palm cultivation, lowers the water table, exposes peat to oxygen, and accelerates both carbon loss and nitrogen cycling. The net effect of this conversion on nitrous oxide emissions had remained unclear, in part because tropical peat nitrogen dynamics are complex and because measurements have traditionally focused on soils alone. By showing that the intact forest’s sink strength depends partly on processes happening in the canopy, the study suggests that conventional bottom-up emission inventories may miss a significant component of the nitrous oxide cycle in tropical forests.

For conservation and climate policy, the message is twofold. First, protecting pristine peat swamp forests preserves not only their carbon stocks but also a microbial machinery that suppresses nitrous oxide, with soils acting as near-complete sinks and tree leaves contributing up to two-thirds of the ecosystem’s uptake of the gas. Second, the findings underscore that restoration efforts may need to consider re-establishing specific tree species and their associated microbiomes, not simply rewetting the soil. The work was supported by the European Union Horizon program, the European Research Council, and Estonian research funding bodies, and was carried out with fieldwork assistance from the Sarawak Tropical Peat Research Institute. As oil palm expansion continues across the region, the invisible communities of bacteria on leaves and in peat may prove to be decisive arbiters of how much nitrous oxide these landscapes send into the atmosphere.

Subject of Research: Microbial nitrous oxide consumption in tropical peatland soils and tree canopies under land conversion to oil palm

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

Article References: Kuusemets, L., Khanongnuch, R., Mander, Ü., Öpik, M., Melling, L., Kikas, K., Pärn, J., Soosaar, K., & Espenberg, M. (2026). Land conversion impacts on soil and above-ground microbial nitrous oxide consumption in tropical peatlands. Biogeochemistry. https://doi.org/10.1007/s10533-026-01379-z

Image Credits: AI Generated

DOI: 10.1007/s10533-026-01379-z

Keywords: tropical peatlands, nitrous oxide, oil palm plantation, peat swamp forest, microbial ecology, metagenomics, nitrogen cycle, greenhouse gases, Sarawak, land-use change, ammonia-oxidizing bacteria, soil emissions