Nitrous oxide (N₂O) is a powerful greenhouse gas and the main driver of stratospheric ozone depletion. Since soils are the largest source of N₂O, predicting soil response to changes in climate or land use is central to understanding and managing N₂O. Here we find that N₂O flux can be predicted by models incorporating soil nitrate concentration (NO₃⁻), water content and temperature using a global field survey of N₂O emissions and potential driving factors across a wide range of organic soils. N₂O emissions increase with NO₃⁻ and follow a bell-shaped distribution with water content. Combining the two functions explains 72% of N₂O emission from all organic soils. Above 5 mg NO₃⁻-N kg⁻¹, either draining wet soils or irrigating well-drained soils increases N₂O emission by orders of magnitude. As soil temperature together with NO₃⁻ explains 69% of N₂O emission, tropical wetlands should be a priority for N₂O management.

Methane flux from freshwater mineral‐soil (FWMS) wetlands and its variability among sites is largely modulated by plant‐mediated transport. However, plant‐mediated transport processes are rarely resolved in land surface models and are poorly parametrized for plants commonly found in FWMS wetlands. Here, relationships between methane flux and CO₂ uptake, as well as plant conductance of methane were evaluated for three plant species and two characteristic functional types: emergent (narrow‐leaved cattail) and floating‐leaved (American lotus and water lily). We found significant but contrasting correlations between methane flux and CO₂ uptake in cattails (r² = 0.51, slope = −0.16, during morning) and water lily (r² = 0.32, slope = 0.064, after midday). This relationship was not significant in American lotus, showing that stomata regulation of methane fluxes is species‐specific and not generalizable across the floating‐leaved plant functional type. Conductance of methane per leaf area showed distinct seasonal dynamics across species. Conductance was similar among the floating‐leaved species (6.2 × 10⁻³ m d⁻¹ in lotus and 7.2 × 10⁻³ m d⁻¹ in water lily) and higher than conductance in the emergent species (2.7 × 10⁻³ m d⁻¹). Our results provide direct observations of plant conductance rates and identify the vegetation parameters (leaf area, stomatal conductance) that modify them. Our results further suggest that models of methane emissions from FWMS should parameterize plant‐mediated transport in different plant functional types, scaled by leaf area and with variable seasonal phenological dynamics, and consider possible species‐specific mechanisms that control methane transport through plants.

Current estimates of wetland contributions to the global methane budget carry high uncertainty, particularly in accurately predicting emissions from high methane-emitting wetlands. Microorganisms drive methane cycling, but little is known about their conservation across wetlands. To address this, we integrate 16S rRNA amplicon datasets, metagenomes, metatranscriptomes, and annual methane flux data across 9 wetlands, creating the Multi-Omics for Understanding Climate Change (MUCC) v2.0.0 database. This resource is used to link microbiome composition to function and methane emissions, focusing on methane-cycling microbes and the networks driving carbon decomposition. We identify eight methane-cycling genera shared across wetlands and show wetland-specific metabolic interactions in marshes, revealing low connections between methanogens and methanotrophs in high-emitting wetlands. Methanoregula emerged as a hub methanogen across networks and is a strong predictor of methane flux. In these wetlands it also displays the functional potential for methylotrophic methanogenesis, highlighting the importance of this pathway in these ecosystems. Collectively, our findings illuminate trends between microbial decomposition networks and methane flux while providing an extensive publicly available database to advance future wetland research.

Wetlands are the most important natural source of methane (CH₄) to the atmosphere, and there is still considerable uncertainty of CH₄ flux and net carbon budgets of wetlands. This uncertainty is due in part to the complex role of wetland vegetation in controlling methane production, oxidation and transport, which challenge the modeling and forecast of CH₄ fluxes. We combined CH₄ and carbon dioxide (CO₂) fluxes measured by the eddy covariance technique during two consecutive growing seasons with continuous measurements of water levels and water temperature in a Typha angustifolia L patch of a temperate wetland. We seek to evaluate the role of vegetation in CH₄ flux processes. To this end, we determined the relationship between CH₄ and CO₂ fluxes, directly and indirectly linked to plant activity. Our results indicated significant but opposing relationships between CH₄ and CO₂ fluxes during the daytime and nighttime. Consequently, when analyzed on a diel timescale, this relationship was not significant. Both CH₄ and CO₂ fluxes were highly dependent on environmental drivers, and thus, the correlations observed at both the nighttime and daytime were likely the result of a shared response to environmental variables. Focusing on water temperature (the most commonly observed environmental variable in wetlands) and water level (the most commonly controlled one) as operational control variables for wetlands, we identified “hot” condition combinations when CH₄ flux and net ecosystem CO₂ uptake are maximized at half hourly and diel scales.