Global warming accelerates the breakdown of carbon stored in permafrost regions, releasing it into the atmosphere and amplifying climate change, particularly during winter when photosynthesis ceases. The Northern Hemisphere's permafrost is primarily concentrated in two key regions — the Arctic and the Tibetan Plateau — each with distinct environmental characteristics. However, previous studies often treat these regions separately, missing the opportunity to compare their winter CO2 emissions within a unified framework. Here, we synthesized 2,487 monthly CO2 flux measurements from 166 in-situ sites to quantify the spatial and temporal variations and key drivers of winter CO2 emissions in these two regions. Our analysis reveals that combined winter emissions from the Arctic and Tibetan Plateau are estimated to be 1,289 ± 25 Tg C yr-1. From 1982 to 2022, winter CO2 emissions increased by 2.10 ± 0.23 Tg C yr-1. Notably, since 2001, winter CO2 emissions have surged in the Arctic while declining in the Tibetan Plateau. The driving factors also differ: soil temperature dominates in the Arctic (51%), whereas soil moisture plays the most significant role on the Tibetan Plateau (33%). These findings highlight the contrasting mechanisms governing winter carbon emissions in these regions and underscore the importance of incorporating region-specific factors when predicting permafrost-carbon feedbacks in a warming world.

Arctic tundra soils can act as an important sink for atmospheric methane (CH4). However, the role and magnitude of this process, and how it will change during future climate scenarios, are poorly understood. The vegetation is changing with a warmer Arctic climate, with taller plants, more shrubs, and altered vegetation patterns. These changes are predicted to be strongest in moist to wet regions, areas usually associated with CH4 production. Additionally, these changes in growth patterns can increase evapotranspiration rates, leading to enhanced soil aeration, favouring CH4 oxidation. Here, we investigate CH4 dynamics within long-term (> 25 years) passive air warming treatments, using five plant communities with contrasting soil moisture and nutrient regimes. These treatments reveal a strong increase in atmospheric CH4 oxidation in two dry ecosystems (140.4% ± 8.1% and 204.2% ± 19.3% for a Dry Heath and Dry Meadow, respectively), and a strong reduction of CH4 emissions (91.2% ± 18.6%) in a Tussock Tundra community. In contrast, our investigation of Mesic and Wet Meadows showed no significant treatment effects, with only limited CH4 exchange in the Wet Meadow. Furthermore, when inhibiting CH4 oxidation in the surface soil, we found evidence of CH4 production even at the driest site (Dry Heath), indicating a potential for CH4 production throughout the landscape. Although soil temperature and moisture have been put forward as strong regulators of CH4 fluxes, they did not consistently explain our observed changes. Instead, we argue for interactions between vegetation change and near-surface soil characteristics. The observed shift in plant composition and increased vegetation height, along with warmer air temperatures, enhanced evapotranspiration and surface soil aeration, thereby stimulating methanotrophy and leading to increased CH4 oxidation. This vegetation-induced climate feedback would aid the predicted temperature-dependent increase of CH4 oxidation in the Arctic, potentially mediating CH4 emissions from the region.

Significant changes in vegetation greenness and browning have been observed across the northern permafrost zone, with important implications for ecosystem functioning and carbon uptake. While recent research has improved our understanding of the drivers of greening, the processes behind browning - especially the low-stature shrubs and herbaceous vegetation, which is more directly exposed to soil and atmospheric moisture deficits - remain less clear. To characterize browning patterns, we integrate multiple remote sensing datasets - including normalized difference vegetation index (NDVI), solar-induced chlorophyll fluorescence (SIF), and foliar chlorophyll concentration (FCC) - with gross primary productivity (GPP) simulations from CMIP6 Earth system models (ESM). We identify significant browning trends (-0.033 to - 0.025 decade-1, from MODIS NDVI) from 2001 to 2018, affecting approximately 20 % (~600,000 km2) of the study region. Browning is primarily modulated by compound soil and atmospheric dryness, reflected by declining soil moisture concurrent with increasing vapor pressure deficit. We further show that regional warming and changes in precipitation, together with permafrost-related constraints on infiltration and storage, modulate the spatial heterogeneity of compound dryness. CMIP6 projections suggest that compound dryness is likely to persist or intensify in permafrost ecosystems, implying continued risk of productivity loss, especially when combined with pulse disturbances such as wildfires.

Measurements of surface-atmosphere carbon dioxide (CO2) and methane (CH4) fluxes have been relatively sparse across the Arctic tundra and boreal biomes, causing significant uncertainties in carbon budget estimates from the region. While the availability of Arctic-boreal carbon flux data has increased substantially over the past decade, the data have remained spread across different repositories, scientific articles, and unpublished sources, making it difficult to leverage. Here we present a new dataset of monthly Arctic-boreal carbon fluxes (ABCFlux v2) across terrestrial (wetlands and uplands) and freshwater (lakes and rivers) ecosystems compiled from previous syntheses including the Arctic-boreal CO2 flux database (ABCFlux v1), the Boreal-Arctic Wetland and Lake Methane Dataset (BAWLD-CH4), and the Global River Methane Database (GRiMeDB). In addition, we consider data from general-purpose (e.g., Zenodo) and flux network repositories, literature, and site principal investigators. The dataset includes surface-atmosphere CO2 fluxes of gross primary production (GPP), ecosystem respiration (Reco), and net ecosystem exchange (NEE), alongside CH4 fluxes. For aquatic ecosystems, we split CH4 fluxes into diffusive and ebullitive flux pathways, and included potential emissions from transient storage in the water column (“storage fluxes”), alongside CO2 and CH4 concentrations dissolved in the surface water. Fluxes are measured through a variety of methods including chamber and eddy covariance techniques alongside bubble traps, ice-surveys, and concentration-based turbulence-driven modelling in aquatic ecosystems. The monthly flux data are reported together with supporting methodological and environmental metadata. The resulting ABCFlux v2 has 23 847 flux site-months, 8182 concentration site-months, and 199 seasonal observations from 1024 sites, and includes 56 139 reported fluxes (i.e. sum of GPP, Reco, NEE, and CH4 fluxes) from the years 1984 to 2024. The majority of monthly observations occurred after 1999. Wetlands had the highest number of site-month observations (8758), followed by boreal forest (6981), lotic ecosystems (6275), lentic ecosystems (3799) and upland tundra (3308). Measurements of CO2 dominated the dataset across most ecosystem types (25 222) except for lentic ecosystems, where CH4 flux site-months (3098) were more frequent than CO2 flux site-months (2915). Overall, ABCFlux v2 includes 160 % more site-months for terrestrial CO2 flux data compared to ABCFlux v1. Integrating and updating BAWLD-CH4 flux data from growing season averages to monthly fluxes resulted in 5671 site-months of chamber CH4 data compared to 762 site-years. This collaborative initiative, involving contributions from over 260 researchers, provides a comprehensive overview of the current state of the Arctic-boreal carbon flux network and its data, and serves as an important step in reducing uncertainties in Arctic-boreal carbon budgets and in enhancing our understanding of climate feedbacks. The data can be accessed at ORNL DAAC at https://doi.org/10.3334/ORNLDAAC/2448 (Virkkala et al., 2026).

Topographic depressions within agricultural fields contribute disproportionately to regional nitrous oxide (N2O) emissions. These low-lying areas accumulate nutrients and fine particles through water inflow and erosion, creating conditions conducive to elevated N2O emissions. Because depressions remain part of fields, understanding how crop presence and management influence their N2O source strength is essential. A greenhouse mesocosm experiment was conducted using soil collected from an agricultural depression under either drained or partially waterlogged conditions (water table maintained 10 cm below the soil surface). Wheat was sown at three dates (57, 43, and 29 days before waterlogging) to represent different vegetative stages and capacities for N uptake. Dissolved organic carbon (DOC), dissolved nitrogen (N), root growth, and N2O emissions were continuously monitored. A 15N-labelled fertilizer was applied during the waterlogging period to trace fertilizer-derived N in emitted N2O, soil, and plant biomass. Early-sown wheat was more strongly impaired by waterlogging than later-sown treatments but nevertheless significantly reduced N2O emissions compared with the unplanted control, irrespective of water regime. Early-sown plants also acted as stronger N sink, indicating that greater plant N acquisition contributed to reduced N availability for N2O production. In contrast, trends in DOC and cumulative N2O emissions across seeding dates were less consistent, particularly under waterlogged conditions. Plant N uptake emerged as the primary mechanism reducing N2O emissions under the tested conditions. Although a general trend of lower N2O emissions with increasing plant age and N uptake was observed, the relationship was not strictly linear, due to plant age-specific interactions with waterlogging. Nevertheless, the results suggest that establishing crops in depression areas can mitigate N2O emissions by strengthening plant competition for available N, while the magnitude of this mitigation depends on both seeding date and waterlogging conditions.

Climate change is particularly important in Arctic environments, which are warming faster than the global average. Despite their importance for local biogeochemical cycling and global climate, we have a limited understanding of how warming can affect Arctic soil microbes, and only few studies have examined Arctic soil fungi and bacteria simultaneously or compared the total and active communities. We show the combined effect of simulated summer and winter warming using open-top chambers and snow fences on a tundra soil microbial community in Greenland after one year. The sampling design considers bacteria and fungi, the total (DNA-based) and active (RNA-based) community and changes over the course of a growing season. We observed differences in soil temperature, soil chemical properties and microbial biomass between warming treated sites and controls. Warming significantly affected microbial community composition with a larger effect on fungi compared to bacteria. However, warming only explained 2.6 and 5.7

Soils across permafrost regions are one of the largest terrestrial pools of mercury (Hg) in the world, storing an estimated 500-1500 Gg of Hg in the top three meters of soil. Ongoing climate-driven thaw threatens to release this legacy Hg into the environment. Efforts to quantify and model this pool have been hindered by a lack of harmonized, spatially resolved observations. To address this, we compiled a database of 117,802 Hg observations collected between 1988 and 2022 from 59 studies across Arctic, sub-Arctic, and alpine permafrost regions of the Northern Hemisphere, including North America, northern Europe, Eurasia and the Tibetan Plateau. The database includes Hg concentration measurements in solid materials - such as soil, leaves, roots, and wood - as well as in water samples from soil porewater, lakes, and rivers across the northern hemisphere permafrost domain. The database enables cross-site synthesis, model calibration and evaluation, and environmental assessments by standardizing and harmonizing data from diverse sources. Data standardization included unit conversion, categorization of observations by type, and quality-control procedures to ensure consistency across studies. Analytical uncertainty was preserved where reported in source studies, and quality control indicators - including range and outlier flags - were applied to support data screening and interpretation. Mercury concentrations vary widely across observations, with lake sediment showing the highest median values (70 ng g-1, IQR: 45-116), followed by soil (50 ng g-1, IQR: 32-90), and vegetation (15 ng g-1, IQR: 9-33). Water observations (total Hg) had a median of 2 ng L-1 (IQR: 2-6). Statistically significant differences in Hg concentrations among observation types were observed at both global and regional scales, generally following the pattern: lake sediment > soil > vegetation, although this ordering is sensitive to regional sampling distribution. These patterns, along with spatial and observation-type biases, highlight the need for improved coverage in underrepresented regions such as Eurasia. The database is freely accessible through Zenodo under the concept 10.5281/zenodo.18300989 (all versions; Olson et al., 2026a), to support ongoing research and model development in Arctic and sub-Arctic Hg cycle studies.

Rewetting is widely promoted as a climate mitigation strategy to preserve soil carbon in drained wetlands, although rewetting may enhance methane production and corresponding emissions. The increase in methane emissions following rewetting might be underestimated without considering near-surface methane oxidation under a fluctuating water table. Here, we refined the methane module in Lund-Potsdam-Jena General Ecosystem Simulator with high-affinity methane oxidation and oxygen parameterization involving water table fluctuations. During 2007-2023, the Danish temperate wetland site functioned as a carbon dioxide sink (−41 gC-CO2m-2yr⁻1) and a methane source (0.71 gC-CH4m⁻2yr⁻1), with significant declines in seasonal amplitudes of methane flux, net ecosystem exchange, and gross primary productivity. Scenario analysis shows maintaining a stable water table at 9 cm depth offers the optimal trade-off between carbon sequestration and methane release. Our findings reduce the uncertainty in wetland methane estimates under climate change and highlight the importance of site-specific rewetting strategies to optimize mitigation efforts. Observations and model work from a Danish temperate wetland during 2007-2023 indicate that the site acted as a carbon dioxide sink and a methane source, and a stable water table at about 9 cm depth can be recommended as the best rewetting solution

Rice paddy soils are a significant source of methane (CH4). Nitrous oxide (N2O) is another potent greenhouse gas (GHG) but its significance to GHG balance in rice paddies remains uncertain. Here, we present high-resolution measurements of CH4 and N2O using automated chambers, combined with subsurface O2 concentrations, over a fallow period and a cabbage-growing season in a subtropical rice-vegetable rotation system. The combination of automated chambers, subsurface oxygen profiling, and LandscapeDNDC modelling calibrated to measured O2 dynamics provides unprecedented mechanistic insight into N2O hot moments in rice–vegetable rotations. Episodic "hot moments" dominated N2O emissions, with 72% of total seasonal flux occurring within 27% of the cabbage season. Mean and peak N2O fluxes during cabbage cultivation reached 104 µg N2O-N m−2 h−1 and 682 µg N2O-N m−2 h−1, respectively. High-emission events were linked to fertilisation, changes in water-filled pore space and subsurface oxygen availability, with N2O fluxes initially dominated by denitrification under saturated conditions and later by nitrification as nitrate and oxygen increased and ammonium decreased. This conclusion was supported by LandscapeDNDC. The emission factor for nitrogen applied was 0.52%, and nitrogen use efficiency was 38%. Total N2O emissions during cabbage cultivation were sevenfold higher than fallow, whereas CH4 fluxes remained unchanged. The global warming potential (GWP) in cabbage was driven by N2O rather than CH4. These findings highlight the importance of capturing N2O emission events in paddy-to-vegetable transition systems and the value of process-based modelling to identify dominant biogeochemical pathways.

In recent decades, the temperature and precipitation patterns in Arctic ecosystems have been highly affected by climate change. Previous studies suggest that changing air circulation and more evaporation from ice-free Arctic seas could increase snowfall and winter snow accumulation in parts of the Arctic, which in turn can change the onset of the growing season. In combination with ongoing and projected temperature rise, such shifts will alter the physical and biogeochemical processes that are associated with soil respiration and production/release of greenhouse gases like CO2 from Arctic tundra soils.Arctic tundra soils experience strong seasonal hydrological dynamics, ranging from frozen conditions in winter to near water saturated and partially water saturated conditions following snowmelt infiltration in early spring. These conditions exert controls (i) on the transport behavior and delivery of O2 into the soil, (ii) on the kinetics of soil respiration and (iii) on the release of CO2 to the atmosphere. Despite the importance of these complex interactions for Earth’s climate, there is still a considerable limitation on the accurate quantification of the interplay between thermo-hydrological, transport and microbial respiration in controlling CO2 emissions from tundra ecosystems under transient field conditions.We investigated how physical and biogeochemical processes, including oxygen transport, soil respiration and CO2 emissions respond to seasonal thermo-hydrological dynamics in a typical well-drained Arctic tundra ecosystems by combining lab experiments and field observations with process-based modelling. Our results show that respiration and CO₂ emissions are strongly constrained by low temperatures during most of the year as oxygen concentration remains close to atmospheric levels and therefore oxygen availability is not a limiting factor. The onset of spring is accompanied by a gradual increase in temperature and melting of snowpack, which reduces the thermal limitation on soil respiration. However, the resulting snowmelt infiltration exerts a series of biochemical and physical controls on soil respiration dynamics and CO2 emission by (i) inducing water saturated conditions in soil; (ii) limiting oxygen transport into the soil and CO2 migration toward the atmosphere due to slow gas diffusivity in water and (iii) reducing oxygen concentration to values close to half saturation constant of oxygen, thereby exerting metabolic constrains. These results highlight the importance of considering the impact of climate forcing (e.g., thermal and hydrological dynamics) on physical and biogeochemical processes that regulate carbon dynamics in Arctic tundra ecosystems.

Knowledge of Arctic soil microbiology and its role in nitrogen (N) cycling is increasing, but research has largely focused on the short summer season. Winter warming (WW) events in the Arctic might cause vegetation browning, but how such events can affect soil microbial functioning and composition is unknown. Therefore, we performed a field experiment with in-situ WW in a dry Arctic heath in Blæsedalen, Disko Island, West Greenland. The aim was to test if N uptake by soil microbes during a week-long in situ experimentally induced WW event could be observed and if this WW caused legacy effects on microbial N uptake and bacterial abundance the following summer. In this pioneering experiment testing the applicability of nanoSIMS, soil was labelled with 15N enriched ammonium during WW in April. Later, in August, we used a 15N enriched amino acid mixture, to further test microbial uptake. The method concept was successful, as both 15N substrates were taken up by living microbes. Our results indicated that N uptake by living bacteria contributes to N cycling and availability during WW. Furthermore, we observed a bacterial legacy effect in summer, with higher bacterial abundance in soils subjected to WW compared to non-warmed plots.

European wetlands store large carbon reserves1, but centuries of land use have eroded carbon stocks and biodiversity2. The European Union (EU) Nature Restoration Law (NRL)3 requires at least 30% of wetland ecosystems not in 'good condition' to be restored by 2030, yet spatially consistent information on wetland types and condition remains scarce. Using 10-m satellite imagery and machine learning, we map six seminatural open wetland types and land-use disturbance across 38 European countries. Wetlands are highly fragmented, with an estimated 27-33% of wetland area occurring in map-defined patches <25 ha and 7-11% in patches <1 ha, exposing many small sites missed by coarser products. We estimate that human activities affect 20.4 ± 3.4% of wetland areas (95% confidence interval), with inland wetland types most affected, and up to 5 Gt CO2-eq of soil carbon potentially lost relative to an undisturbed baseline. Translating disturbed area into NRL restoration targets, we find that several countries' pledges are broadly consistent with our 2030 estimates, whereas others lack quantified commitments despite substantial candidate areas identified by our maps. The resulting standardized, high-resolution products provide an EU-wide baseline tailored to the NRL and a reproducible template for linking satellite mapping to restoration targets, supporting progress tracking.

Abstract Arctic tundra ecosystems have experienced marked changes in temperature and precipitation patterns in recent decades. The impact of these changes on the physical and biogeochemical mechanisms governing soil respiration and CO2 emissions remains poorly understood. We investigate how seasonal thermo–hydrological dynamics impact soil freezing/thawing, soil respiration, and O2 and CO2 transport and exchange in a typical well-drained Arctic tundra ecosystem by combining laboratory experiments and field observations with process-based modeling. Our results demonstrate that low temperatures constrain soil CO2 production and efflux during most of the year, but rising temperatures and large snowmelt infiltration in early spring reduce thermal constraints and induce relatively short yet important periods of soil water-saturated conditions. During these periods, depth-resolved measurements show noticeable limitations in oxygen transport and corresponding CO2 production, which leads to the reduction of CO2 effluxes. The snowmelt infiltration also reduces CO2 efflux by promoting downward CO2 migration and delays its emission by limiting diffusive transport to the atmosphere until the water level recedes. Comparing the simulations with a no-snowmelt scenario, we find that these physical and biogeochemical controls during such short periods collectively reduce annual CO2 efflux by 7%, highlighting the importance of climate-driven forcing in modulating soil greenhouse gas emissions.

Aim: Rapid warming across the tundra biome is driving widespread changes in vascular plant community composition. While species turnover is well-documented, the ramifications for tundra functional diversity are unknown. Here, we quantify biome-scale spatial gradients and temporal trends in the functional diversity of tundra vegetation for the first time. Location: A biome-scale synthesis of in situ vegetation surveys and resurveys from 2087 plots across 45 sites throughout the high-latitude tundra. Time Period: 1984-2022 Major Taxa Studied: 352 vascular plant species encompassing shrub, graminoid and forb functional groups Methods: We used tundra species trait data alongside long-term, plot-based sampling of species composition to estimate three functional diversity metrics: functional richness, functional evenness and functional dispersion. We used Bayesian mixed-models to test for latitudinal gradients in functional diversity, temporal trends in functional diversity and major abiotic and biotic correlates of functional diversity over space and time. Results: Mirroring biogeographic gradients in species diversity, functional richness declined at high latitude and colder sites. However, functional richness exhibited no net directional change across the three-decade study period. Plots dominated by single growth forms had reduced functional diversity when compared with plots where individual growth forms had intermediate abundance. Changes in temperature and precipitation were not linked to temporal changes in functional diversity. Where shrubs were increasing in abundance, functional richness and dispersion declined, whereas increases in forbs were accompanied by increases in both aspects of functional diversity. Main Conclusions: The functional diversity of tundra plants is currently lowest in colder and high latitude sites. Despite rapid warming of the tundra biome, we have yet to see broad-scale changes in functional diversity over time. However, where shrubification occurs, we anticipate accompanying reductions in functional diversity. Our results highlight the potential consequences of changes in tundra species composition for ecosystem functioning over the coming decades.

Arctic regions experience an unprecedented warming due to global climate change. However, the impact of increased summer temperatures on the soil prokaryotic community remains poorly understood. These microorganisms play a central role in organic matter decomposition and regulation of biogeochemical cycles. Here, we investigated the short-term responses of the prokaryotic community inhabiting the dry tundra soil of West Greenland to elevated summer temperatures simulated by open-top chambers. This study uniquely combines seasonal sampling during the plant-growing season (three time points) with analysis of both total and potentially active prokaryotic communities, together with quantification of functional genes involved in nitrogen (N) and methane (CH4) cycling processes, providing an integrated assessment of how warming influences microbial community structure and function in Arctic soils. Our results revealed pronounced seasonal shifts in soil nutrient availability and chemical properties, which were accompanied by significant changes in microbial biomass and prokaryotic community composition. The abundance of genes encoding key steps in N fixation, nitrification, methanotrophy and methanogenesis increased significantly from June to July, indicating enhanced microbial activity during the peak growing period. The short-term warming treatment had a significant positive effect on soil organic matter (SOM) content and microbial biomass N and affected both total and potentially active prokaryotic community structure. Notably, substantial differences between total and potentially active communities were observed, indicating that prokaryotic taxa with low abundance can be highly active in the Arctic soil environment.

The history of Greenland is marked by different waves of Paleo-Inuit immigration from North America from 2,500 BC to the 12th century and from the 10th to 15th century, Norse settlers immigrated from Northwest Europe and flourished in Southwest Greenland with the introduction of domestic livestock. The different Inuit and Norse cultures created middens by dumping and accumulating domestic waste; a latent source of microbes, including potential pathogens, that might have been preserved due to the general wet and cold conditions in the region. The aim of this study was to evaluate whether ancient Arctic settlements might be possible hot-spots for pathogenic agents that may spread to the surrounding environment because of current climate changes. Using metagenomics, we compared the microbial communities and resistomes of 78 samples from middens from different ages and locations in West and South Greenland (two Paleo-Inuit, four Norse and one early Colonial-time middens) to 143 soil samples from nearby surroundings. We found that the middens harbor a distinctive microbial signature enriched in human-associated bacteria. Those include opportunistic pathogens such as Clostridium perfringens and Paeniclostridium sordellii. In some early colonial midden layers, C. perfringens and Paraclostridium tenue together accounted for up to ~40%–50% of MetaPhlAn-derived relative abundance in individual samples. Antimicrobial resistance genes representing 17 resistance classes were detected across all sites, dominated by β-lactam and tetracycline resistance. Transect analyses across an actively eroding midden showed that midden-derived bacteria were confined to local erosion layers and were rapidly replaced by native marine communities, indicating limited environmental dispersal.

Global warming accelerates the breakdown of carbon stored in permafrost regions, releasing it into the atmosphere and amplifying climate change, particularly during winter when photosynthesis ceases. The Northern Hemisphere's permafrost is primarily concentrated in two key regions — the Arctic and the Tibetan Plateau — each with distinct environmental characteristics. However, previous studies often treat these regions separately, missing the opportunity to compare their winter CO2 emissions within a unified framework. Here, we synthesized 2,487 monthly CO2 flux measurements from 166 in-situ sites to quantify the spatial and temporal variations and key drivers of winter CO2 emissions in these two regions. Our analysis reveals that combined winter emissions from the Arctic and Tibetan Plateau are estimated to be 1,289 ± 25 Tg C yr-1. From 1982 to 2022, winter CO2 emissions increased by 2.10 ± 0.23 Tg C yr-1. Notably, since 2001, winter CO2 emissions have surged in the Arctic while declining in the Tibetan Plateau. The driving factors also differ: soil temperature dominates in the Arctic (51%), whereas soil moisture plays the most significant role on the Tibetan Plateau (33%). These findings highlight the contrasting mechanisms governing winter carbon emissions in these regions and underscore the importance of incorporating region-specific factors when predicting permafrost-carbon feedbacks in a warming world.

Background and aimsEastern Denmark’s agricultural landscapes feature numerous topographic depressions that are frequently flooded during late winter and spring. These poorly drained, carbon- and nitrogen-rich depression soils receive eroded material from adjacent slopes. Fertilization and water saturation create N2O emission hotspots. However, the potential legacy effects of these topographic locations on microbial communities involved in N2O production and reduction remain unclear. One approach to mitigating high denitrification rates (as a source of N2O) is to alter microbial pathways by adding nonhazardous levels of copper.MethodsWe conducted an incubation study using upland and depression soils from the same site, incorporating varying Cu levels (0, 130, and 260 mM) and water levels (60% and 90% water holding capacity).ResultsDepression soils emitted eight times more N2O than upland soils at 90% WHC. Cu addition did not reduce cumulative N2O emissions but delayed or lowered the flux peak. Depression soils exhibited 3,000- and 4,000-fold higher 16S rRNA and nosZ clade I abundances, respectively, compared to upland soils. Cu addition significantly decreased 16S rRNA abundance, eliminated AOB amoA in upland soils, and slightly reduced the tested gene abundances in depression soils. The nosZ gene community structure differed significantly between the two soils.ConclusionsOverall, our study suggests that erosional differentiation of soil properties, together with frequent waterlogging conditions, can result in distinct microbial communities, fostering legacy effects that lead to differences in N2O emissions between upland and depression soils. Adding Cu to these intensively managed soils is unlikely to be an effective strategy for mitigating N2O emission hotspots in arable fields.

Methane (CH 4 ) oxidation in well‐drained soils is a key process contributing to the global CH 4 sink. Yet, temporal and depth‐specific CH 4 oxidation is rarely described despite being critical for the surface net CH 4 uptake. Here, we linked year‐round field observations of CH 4 fluxes in well‐drained cultivated soils with subsurface CH 4 concentrations, laboratory incubations, and process‐based modeling to uncover these mechanisms. Field observed CH 4 fluxes ranged from −0.43 to 0.19 mg CH 4 m −2 day −1 with an average of −0.15 ± 0.01 mg CH 4 m −2 day −1 over the year‐round study period. Much higher CH 4 uptakes were observed in summer than in winter, indicating marked seasonal variations. Modeling using the CoupModel to simulate soil temperatures and water content as drivers, along with an analytic reaction‐based model to simulate CH 4 fluxes, shows that the depth infiltration of atmospheric CH 4 is a critical parameter for defining a CH 4 oxidation reaction zone below the surface. The thickness of the reaction zone varied seasonally. Sensitivity tests of CH 4 concentrations and oxidation profiles in response to contrasting precipitation scenarios reveal that CH 4 oxidation during drought scenarios is increased at deeper depths due to higher CH 4 availability. However, CH 4 oxidation in near‐surface layers decreased due to low soil water content, resulting in a significantly lower net surface CH 4 uptake. Our findings suggest that both the depth‐specific CH 4 oxidation profile and net surface CH 4 fluxes will likely change under future warmer and drier periods.

The Arctic–Boreal Zone is rapidly warming, impacting its large soil carbon stocks. Here we use a new compilation of terrestrial ecosystem CO2 fluxes, geospatial datasets and random forest models to show that although the Arctic–Boreal Zone was overall an increasing terrestrial CO2 sink from 2001 to 2020 (mean ± standard deviation in net ecosystem exchange, −548 ± 140 Tg C yr−1; trend, −14 Tg C yr−1; P < 0.001), more than 30