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The wetland soil microbiome has a major impact on greenhouse gas emissions. Here the authors characterize how a group of archaea contribute to N2O emissions and find that climate and land use changes could promote these organisms.

Abstract Riparian forests are known as hot spots of nitrogen cycling in landscapes. Climate warming speeds up the cycle. Here we present results from a multi-annual high temporal-frequency study of soil, stem, and ecosystem (eddy covariance) fluxes of N2O from a typical riparian forest in Europe. Hot moments (extreme events of N2O emission) lasted a quarter of the study period but contributed more than half of soil fluxes. We demonstrate that high soil emissions of N2O do not escape the ecosystem but are processed in the canopy. Rapid water content change across intermediate soil moisture was a major determinant of elevated soil emissions in spring. The freeze-thaw period is another hot moment. However, according to the eddy covariance measurements, the riparian forest is a modest source of N2O. We propose photochemical reactions and dissolution in canopy-space water as reduction mechanisms.

Tree stems in tropical peat swamp forests are known as considerable methane (CH4) emitters; however, little is known about their carbon dioxide (CO2) and nitrous oxide (N2O) exchange. Differences between species, especially the role of palm stems in the exchange of greenhouse gasses, have remained largely unknown. We measured stem CO2, CH4, and N2O fluxes from the different heights of widely spread aguaje palms (Mauritia flexuosa) and boarwoods (Symphonia globulifera) and the soil beneath the same trees in a Peruvian Amazon palm swamp using a static closed chamber technique from September 2019 to March 2020. The tree stems were the net emitters of CO2 and CH4 but occasionally showed low N2O uptake. We found the highest stem CH4 emissions (average ± SE) from palm stems of the height of 80 cm (1,601 ± 165.9 μg C m–2 h–1), which are more than 300 times greater compared to the highest fluxes from boarwood stems, at the height of 30 cm (5.12 ± 1.27 μg C m–2 h–1). The average soil CH4 flux was 3,618 ± 465 μg C m–2 h–1. Whereas N2O fluxes from the stems were negligible, the average N2O fluxes from soils beneath the same trees were relatively high, ranging from 53.75 ± 24.04 (close to boarwood trees) to 143.4 ± 68.43 (close to palms) μg N m–2 h–1. While roughly upscaling tree-level fluxes to the stand level of 27,732 km2 of palm swamp in the Pastaza-Marañon foreland basin, these forests are net annual emitters of CH4 and N2O (897 Gg C y–1 and 24 Gg N y–1, respectively). These results highlight the necessity to study this kind of ecosystem more intensely.

In a global field survey across a wide range of organic soils, the authors find that N2O flux can be predicted by models incorporating soil nitrate concentration (NO3 –), water content and temperature. N2O emission increases with NO3 – and temperature and follows a bell-shaped distribution with water content.

The original version of this Article contained an error in the first sentence of the Acknowledgements section, which incorrectly referred to the Estonian Research Council grant identifier as “PUTJD618”. The correct version replaces the grant identifier with “PUTJD619”. This has been corrected in both the PDF and HTML versions of the Article.