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over the past decade, the data have remained spread across different repositories, scientific articles, and unpublished sources, making it difficult to leverage.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).

The central Congo Basin hosts the world's largest tropical peatland complex, storing 29.0 Pg of carbon, the equivalent to three years of global CO₂ emissions. These peatlands are significant natural sources of greenhouse gases (GHGs), including CO₂, CH₄ and N₂O, but the environmental controls on their emissions remain poorly understood. To address this, we collected surface peat samples from six regional landscapes, spanning palm- and hardwood-dominated sites, and incubated them under three hydrological regimes: flooded aerobic, flooded anoxic and mesic (aerobic and no surface water). This allowed us to quantify how hydrology and peat chemistry (carbon, nutrients and organic chemistry) influence GHG dynamics. We observed strong differences in GHG production between vegetation types, and high sensitivity to hydrological change. Using random forest models, we assessed 27 potential drivers of GHG fluxes, identifying distinct controls across GHGs and hydrological regimes. Incubation of deeper peat samples (up to 1.5 m) highlighted that surface layers dominate peat GHG production. Taken together, our findings demonstrate that hydrology, vegetation, nutrients and peat organic chemistry shape regional GHG emissions, driving substantial spatial variability. Changes to peatland hydrology, for example from land use or climate change, could significantly shift GHG balances, with important implications for global climate feedbacks. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.

One of Earth's most extensive tropical peatland complexes is in the central Congo Basin. Past climatic drying caused the widespread loss of a large proportion of the peat carbon stock, indicating its vulnerability to climate change. However, the additional effect caused by the interaction of climate change with land-use change-particularly drainage-on peat carbon stores has not been assessed. Here, we simulate the effects of climate and land-use change on Congo Basin peatlands. Our model is driven by an ensemble of 10 climate models to assess changes in peat carbon stocks at global warming levels 1.5, 2, 3 and 4°C. We find that the fate of the peatland carbon store is highly uncertain when we simulate climate change alone (warming level 3°C gives a median change in peat thickness of 0.04 m; range of approx. -5.0 to +0.3 m). By contrast, simulations that couple land-use change with twenty-first-century climate change are unequivocal: the Congo Basin peatlands will become significant emitters of carbon. When the warming level is 3°C, the change in peat thickness of a drained peatland is projected to be -2.6 m; a range of approximately -5.0 to -2.1 m. Our results emphasize the need to protect Congo Basin peatlands from widespread land-use change. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.

The peat swamp forests of the central Congo Basin represent the largest, most carbon-rich peatland complex in the tropics. The maintenance of peat carbon stocks and accumulation relies on persistent soil saturation, yet the hydrological functions of tropical peatlands remain poorly understood, particularly in the central Congo Basin. We report the first measurements of saturated hydraulic conductivity (K sat) from Congolese peats. We used Mini Disk tension infiltrometers to estimate K sat at depths of 0 and 10 cm across three study areas in the Democratic Republic of the Congo. K sat ranged from 1.55 & times; 10-5 to 5.75 & times; 10-4 m s-1, with a mean of 1.78 & times; 10-4 m s-1. A general linear model revealed significantly higher K sat at the surface than at 10 cm depth, while K sat is negatively related to degree of peat humification. However, K sat did not vary between palm, hardwood and mixed forest types, or with proximity to rivers (a proxy for flooding regime). Although our linear model is not sufficiently skilful to predict K sat reliably, our findings suggest that a generalisable model for tropical peat K sat may be attainable with larger datasets that span greater ranges of depths and levels of decomposition. Notably, our surface K sat values are lower than those from deeper layers in Southeast Asia and the Americas, implying lower depth-integrated permeability in peats of the central Congo Basin. This may reflect low rainfall and deeper water tables in the region, which would enhance decomposition and reduce pore space more rapidly.

Wetlands, as the largest natural source of methane (CH₄) emissions, have received increasing attention in climate modelling. Recognising that methanogenesis is governed by anaerobic microbial processes, some models explicitly represent methanogen activity to simulate CH₄ emissions from permanently inundated wetlands. In such models, CH₄ emissions from seasonally flooded wetlands are usually estimated using an empirical oxidation factor to represent methanotrophic consumption. However, this approach neglects an additional important effect of atmospheric oxygen ingress during hydrological drawdown: the stimulation of organic matter decomposition upon rewetting, analogous to the Birch effect in seasonally dry ecosystems.Despite the high annual methane emissions from permanently inundated sites, some of the highest intensity CH₄ emission spikes throughout the year are exhibited by seasonally inundated systems, such as freshwater marshes, floodplain wetlands and fens. Consequently, improved mechanistic representation of biogeochemical processes in seasonally inundated wetlands is needed to robustly assess global wetland greenhouse gas contribution.This study presents a process-based wetland biogeochemical model that explicitly represents oxygen-stimulated substrate dynamics and microbial functional differentiation. Dissolved organic carbon (DOC) is partitioned into a “dry DOC” pool that accumulates during dry periods, and a “wet DOC” pool that is replenished upon rewetting. Microbial processes include distinct aerobic and anaerobic pools, whose activities are regulated by soil water content (SWC). Aerobic microbial activity follows a Gaussian response to SWC, reflecting optimal activity under intermediate moisture conditions. Water table depth (WTD), a relatively commonly measured wetland metric, is used to infer vertical SWC profiles in the soil column through a fitted van Genuchten soil water retention curve.The microbial-DOC framework is coupled with the Joint UK Land Environment Simulator (JULES), a community land-surface model simulating the exchanges of energy, water and carbon between the land surface and the atmosphere, which can also be used as the land surface scheme of the UK Earth System Model (UKESM). JULES drives the microbial-DOC module by providing partitioned pools of litter, soil organic carbon, and root exudates, each characterised by distinct turnover kinetics. Temperature sensitivity is represented using Arrhenius kinetics, while substrate and microbial limitations are described using Michaelis–Menten formulations. Model parameters are constrained using methane and carbon dioxide flux measurements, alongside methanogen abundance data, from flooded hardwood and palm forests in Panama.Resolving oxygen-mediated substrate priming and microbial responses, the framework moves beyond oxidation-only representations and improves estimates of wetland carbon source–sink dynamics under climate change.

The cultures and livelihoods of communities whose customary lands include areas of the Cuvette Centrale peatlands are deeply entangled with seasonal rains and flood pulses. We conducted a mixed method qualitative study in a peatland-adjacent fishing camp in Équateur province in the Democratic Republic of Congo's Cuvette Centrale. Mobility is one way that local residents of this fishing camp cope with and adapt to a dynamic hydroclimate. Here, we explore the outcome of different mobility and livelihood strategies on resilience. We first show how local livelihood activities respond to seasonal variability in the local flooding regime. We then show four (im)mobility patterns and their associated livelihood strategies: long-term residents, short-distance mobility, fishing camp-village-town mobility and inter-river mobility. Lastly, we present how resilience outcomes vary using short vignettes of mobility histories of fishing camp residents. We identify the importance of local and translocal social networks as crucial elements for adapting to, and coping with change in a dynamic hydroclimate. Our findings challenge those unfamiliar with the Cuvette Centrale peatlands to avoid applying a sedentary agriculturalist lens to understand livelihood and resilience dynamics. We offer practical suggestions for how to account for mobility in future conservation and research initiatives in the context of the Cuvette Centrale peatlands. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.

The central Congo Basin hosts the world's largest tropical peat swamp forest (PSF), covering 167 600 km² and storing approximately 29 Pg of carbon below ground. However, estimates of above ground biomass (AGB) remain limited, partly owing to reliance on global wood density (WD) databases that may not reflect local species characteristics. This study assessed the impact of species-specific WD on AGB estimation in five PSF sites of the northern Republic of Congo. Specific WD was collected in one site, and these data were then used to estimate AGB in four additional sites. We collected wood cores using an increment borer from 244 trees to measure the WD of the 20 most abundant species (93% of trees with diameters ≥10 cm). Using global WD values overestimated AGB by 24.7% (p < 0.05). The low average local WD (0.460 ± 0.12 g cm-3) explained this difference. The WD variation was primarily species-driven (58%) and associated with functional traits; pioneer and evergreen species had lower WD. These findings highlight the importance of locally measured WD for accurate biomass and carbon stock estimation in tropical peatland forests. A French translation of this abstract is available in the supplementary material. This article is part of the discussion meeting issue 'African tropical peatlands: function, value and vulnerability'.

The central Congo Basin contains the world’s most extensive tropical peatland complex, spanning 16.7 million hectares. Until now, radiocarbon dating of basal peats has been limited to 14 samples with poor spatial coverage, and suggested that peat typically initiated during the Holocene. We present 38 new basal dates, improving spatial coverage across the region. Some of the new basal dates are much older than any previous dates, indicating that peat initiated in the central Congo Basin at multiple locations in the Late Pleistocene. Our oldest basal date is 42 300 (41 200–43 800) calibrated years before present, making this one of the world’s oldest extant tropical peatlands, and twice as old as previously believed. The temporal distribution of basal dates suggests that changing climatic wetness has played a role in peat initiation in the region; numerous basal dates correspond with climatically wet phases, whilst few basal dates correspond with dry phases such as the Last Glacial Maximum (LGM). Today we find the central Congo Basin peatlands on wide interfluves between rivers, and on floodplains (mostly of the dendritic left-bank tributaries of the Congo River). We find the oldest basal dates on the floodplains of these left-bank tributaries, indicating a surprisingly high degree of channel stability over many millennia. This contrasts with, for example, peatlands on Amazonian floodplains, which are typically just a few thousand years old. The persistence of peat in the central Congo Basin since before the LGM, likely the most climatically dry period during the last 42 000 yr in this region, suggests that these areas may have played an important biogeographical role as forest refugia during glacial-interglacial cycles.

Following rapid climate change, tundra plant communities are experiencing extensive compositional shifts. A conservation concern is the potential encroachment of boreal species into the tundra ('borealisation'). Tundra borealisation has been sporadically reported, but not systematically quantified. Here, we synthesised data from across 32 study areas, spanning 1137 plots and 287 vascular plant species, resurveyed between 1981 and 2023. We (i) quantified tundra borealisation as the colonisation and increase in abundance of Boreal and Boreal-Tundra species, (ii) assessed biogeographical, climatic and local borealisation drivers and (iii) identified species contributing to borealisation and their associated traits. Half of the plots experienced borealisation, although borealisation rates were not different to random expectation. Borealisation was greater in Eurasia, closer to the treeline, at higher elevations, in warmer and wetter regions, where climate change was limited, and where initial boreal abundance was lower. Boreal coloniser species were generally short-statured, and more often shrubs and graminoids. Boreal species colonised around three times less frequently than Boreal-Tundra species. Hence, our findings indicate that tundra borealisation is mainly driven by the spread of already established boreal-low Arctic tundra species. These plant community composition changes could have cascading impacts on land-atmosphere interactions, trophic dynamics and Indigenous and local livelihoods.

Savannahs cover 20 % of the global land surface, but there have been few studies of greenhouse gas (GHG) dynamics from savannah soils. Here, we assess potential turnover of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from surface (0-10 cm) and subsurface (20-30 cm) soils from two contrasting tropical savannah sites in the Republic of Congo, Central Africa, under dry (40 % water-filled-pore-space, WFPS) and wet (70 % WFPS) conditions. Under baseline conditions (25 degrees C), we found soils were sources of CO2 and N2O, but a sink for CH4. Assessment of the temperature response of GHG fluxes between 20 and 35 degrees C revealed variable temperature dependences. That is, CO2 fluxes showed a strong temperature response, whereas the temperature response of N2O fluxes was only significant under dry conditions, and no significant temperature response of CH4 fluxes was observed. The temperature quotient (Q10) of soil respiration increased from 1.58 +/- 0.004 to 1.92 +/- 0.006 at sites with lower soil organic carbon contents. The relative increase in N2O with CO2 fluxes across temperatures was significantly influenced by moisture conditions at both sites. No temperature or soil moisture response was observed for CH4 fluxes, collectively implying divergent GHG responses to changing climatic conditions. Using Rock-Eval pyrolysis we assessed the organic chemistry of all soil types, which indicated contrasting degrees of stability of carbon sources between sites and with depth which, alongside significant differences in a range of other soil parameters (including organic matter content, total carbon, total nitrogen, electrical conductivity, and pH), may account for site-specific differences in baseline GHG emissions. Taken together, our results are amongst the first measures of GHG temperature sensitivity of tropical savannah soils, and demonstrate that soil CO2 emissions are more sensitive to warming and changes in moisture than the emissions of other GHGs, although relatively low compared to responses reported for soils from other tropical ecosystems. This implies that GHG fluxes form savannah soils in the region may be at least partially resilient to climate-induced soil warming compared to other ecosystems.

Following rapid climate change across the Arctic, tundra plant communities are experiencing extensive compositional shifts. One of the most prevalent changes is the encroachment of boreal species into the tundra (‘borealization’). Borealization has been reported at individual sites, but has not been systematically quantified across the tundra biome. Here, we use a dataset of 1,137 plots at 113 subsites across 32 study areas resurveyed at least once between 1981 and 2023 and encompassing 287 vascular plant species. We i) quantified the borealization of tundra ecosystems as the colonisation and the increase in abundance of boreal specialist and boreal-tundra boundary species, ii) assessed biogeographical, climatic and local drivers of borealization, and iii) identified species contributing most to borealization and their associated traits. Around half of the plots experienced borealization, especially at sites closer to the treeline, at higher elevations (mountains), in warmer and wetter regions, and at sites that had undergone the lowest magnitude of climate change. Boreal species were more likely to expand in Eurasia, and at sites with lower initial abundances of boreal species. Boreal species that colonised more plots were generally short, and more likely to be shrubs and graminoids than forbs. Boreal specialist species colonised three times less frequently than boreal-tundra boundary species, yet abundance changes were similar across groups. These findings indicate that borealization is mainly driven by the spread of already established species in the tundra, and suggest that future changes to Arctic ecosystems might not involve rapid, widespread replacement of Arctic species by boreal species. These observed and future plant community composition changes could affect land-atmosphere interactions, trophic dynamics and local and Indigenous livelihoods.

Tropical peatlands are carbon-dense ecosystems that are significant sources of atmospheric methane (CH4). Recent work has demonstrated the importance of trees as an emission pathway for CH4 from the peat to the atmosphere. However, there remain questions over the processes of CH4 production in these systems and how they relate to substrate supply. Principally, these questions relate to the relative contribution of recent photosynthetically fixed carbon, released as root exudates, versus carbon substrate supply from the slowly decomposing peat matrix to CH4 emissions within these ecosystems. Here, we examined the role of root inputs in regulating CH4 production inferred from soil emissions using a combination of in situ tree girdling, in situ13C natural abundance labelling via stem injections, and a 13CO2 labelling of transplanted plants of two contrasting plant functional types, a broadleaved evergreen tree, and a canopy palm. Girdling of broadleaved evergreen trees reduced CH4 fluxes by up to 67%. Stem injections of trees and palms with a natural abundance label resulted in significant isotopic enrichment of CH4 fluxes, reinforcing the link between root carbon inputs and peat CH4 fluxes. Ex situ13CO2 labelling of plants resulted in significant 13C enrichment of peat CH4 fluxes. Taken together, our results demonstrate for the first time that plant root exudates make a substantial contribution to CH4 production in tropical peatlands.

The Arctic is warming four times faster than the global average1 and plant communities are responding through shifts in species abundance, composition and distribution2-4. However, the direction and magnitude of local changes in plant diversity in the Arctic have not been quantified. Using a compilation of 42,234 records of 490 vascular plant species from 2,174 plots across the Arctic, here we quantified temporal changes in species richness and composition through repeat surveys between 1981 and 2022. We also identified the geographical, climatic and biotic drivers behind these changes. We found greater species richness at lower latitudes and warmer sites, but no indication that, on average, species richness had changed directionally over time. However, species turnover was widespread, with 59% of plots gaining and/or losing species. Proportions of species gains and losses were greater where temperatures had increased the most. Shrub expansion, particularly of erect shrubs, was associated with greater species losses and decreasing species richness. Despite changes in plant composition, Arctic plant communities did not become more similar to each other, suggesting no biotic homogenization so far. Overall, Arctic plant communities changed in richness and composition in different directions, with temperature and plant-plant interactions emerging as the main drivers of change. Our findings demonstrate how climate and biotic drivers can act in concert to alter plant composition, which could precede future biodiversity changes that are likely to affect ecosystem function, wildlife habitats and the livelihoods of Arctic peoples5,6.

The Congo Basin is home to the world’s largest tropical peatland complex storing 29 PgC across 16.7 million ha, which poses a major unconstrained source of global wetland CH4. Key controls over their spatio-temporal variability remain unclear, limiting our ability to assess responses to future environmental change. Here, we present the first time series of in situ measurements from four intensive locations covering peat, seasonally flooded and terra firma forest ecosystems. Measurements were done every month for two years and additional widespread in situ CH4 flux measurements from the peat surface and from tree stems, across 12 transects distributed across the region. The intensive sites show a substantial CH4 source from hardwood and palm dominated peat swamp forest respectively, representing the most substantial emissions from peat swamp forests globally. These emissions were accompanied by substantial emissions from non-peat forming seasonally flooded forests while emissions were close to zero from the terra firme sites. Temporal variation in emissions were coincident with seasonal variation in the water levels with greater emissions during the wet seasons and little during the dry season. We demonstrate large spatial variation in net CH4 emissions across the region and that net emissions are dominated by peat emissions with only a small overall contribution of tree emissions. The emissions followed an exponential relationship with water levels and higher CH4 emissions occurred in areas closer to the nearest river and in areas with greater river water rather than rainwater inputs. Taken together, our findings demonstrates that the Congo wetlands have the capacity to produce large amounts of CH4 with distinct differences between dominant vegetation communities, and water levels and sources representing a key control over dynamics.

Growing recognition of the potential vulnerabilities of major crop systems has spurred a growing interest in the potential of alternative crops which may be resilient to climate change and also help mitigate its effects. In Indonesia, such issues are particularly pertinent given that country's particular vulnerability to climate change impacts high dependence on agricultural livelihoods and varied topographies and growing conditions. Cyrtosperma merkusii (giant swamp taro) is a wetland plant which has historically formed part of food systems in the eastern Pacific. The plant has the potential to be cultivated as a source of starch on marginal coastal land and on peatlands with high water tables. The aim of this paper was therefore to determine site conditions that promote growth of C. merkusii and the macro and micronutrient status of the corms. Naturally, the size of the plants varied substantially among sites, with a neutral pH, and low redox and conductivity being strong edaphic predictors of corm size. Despite substantial differences in the soil properties of the different study sites, there were no significant differences in the macro and micronutrient content of the corms. Field trials showed that although the plants grew under dry land conditions, the plants grew bigger and yielded corms with greater concentrations of Fe, Mn and K under waterlogged conditions, indicating that a high-water table is the best cultivation environment for C. merkusii. The nutrient content of the corms suggests that, although primarily a starch crop, C. merkusii could also increase the intake of Fe in populations where Fe deficiency is pervasive. We conclude that the wetland plant C. merkusii has considerable potential as a paludiculture crop in low-lying areas of SE Asia as it was tolerant of a wide range of soil conditions and performed well when cultivated under waterlogged conditions without additional fertilisation.

The on-going climate warming is promoting shrub abundance in high latitudes, but the effect of this phenomenon on ecosystem functioning is expected to depend on whether deciduous or evergreen species increase in response to warming.To explore effects of long-term warming on shrubs and further on ecosystem functioning, we analysed vegetation and ecosystem CO2 exchange after 20 years of warming in the forest-tundra ecotone in subarctic Sweden. A previous study conducted 9 years earlier had found increased evergreen Empetrum nigrum ssp. hermaphroditum in the forest and increased deciduous Betula nana in the tundra. Following current understanding, we expected continued increase in shrub abundance that would be stronger in tundra than in forest. We expected warming to increase ecosystem respiration (R-e) and gross primary productivity (GPP), with a greater increase in R-e in tundra due to increased deciduous shrub abundance, leading to a less negative net ecosystem exchange and reduced ecosystem C sink strength. As predicted, vascular plant abundances were higher in the warmed plots with a stronger response in tundra than in forest. However, whereas B. nana had increased in abundance since the last survey, E. hermaphroditum abundance had declined due to several moth and rodent outbreaks during the past decade. In contrast to predictions, R-e was significantly lower in the warmed plots irrespective of habitat, and GPP increased marginally only in the forest. The lower R-e and a higher GPP under warming in the forest together led to increased net C sink. R-e was negatively associated with the total vascular plant abundance. Our results highlight the importance of disturbance regimes for vegetation responses to warming. Climate warming may promote species with both a high capacity to grow under warmer conditions and a resilience towards herbivore outbreaks. Negative correlation between R-e and total vascular plant abundance further indicate that the indirect impacts of increased plants on soil microclimate may become increasingly important for ecosystem CO2 exchange in the long run, which adds to the different mechanisms that link warming and CO2 fluxes in northern ecosystems.