This session aims to bring together scientists studying the CH4 and N2O cycles in forest ecosystems under different climatic, hydrological and scale conditions. This is crucial for improving our understanding of CH4 and N2O exchange in these ecosystems. We welcome contributions on production and consumption processes and mechanisms in soils and plant/tree tissues, as well as gas transport processes within the soil-tree-atmosphere continuum. We highly encourage gas flux measurements from forest soils, cryptogams, tree stems, leaves, and canopies using chamber systems or integrated ecosystem approaches (e.g., flux towers with eddy covariance, satellites, or modelling). We also encourage methodological studies investigating CH₄ and N₂O exchange in forest ecosystems.
Orals: Mon, 4 May, 16:15–18:00 | Room 1.31/32
After carbon dioxide, atmospheric methane is the second most impactful anthropogenic greenhouse gas for global warming. Observations of atmospheric methane in ambient air began in 1978, and now include a wide range of in-situ and remote-sensed observations from the surface, aircraft or from space. Those observations have shown that methane mixing ratio have been multiplied by 2.6 since pr-industrial time and the recent period has experienced record methane growth rate in the atmosphere. This is a well-known and established fact. Questions arise when it comes to methane sources and sinks and the causes of such an increase, sustained by at different rate over time. Different approaches are used to estimates methane sources and sinks: atmospheric inversions use atmospheric mixing ratios measurements to infer methane emissions and sinks (top-down approaches), land-surface models simulate the processes that emit methane at the surface (e.g. wetland and freshwater emissions) or remove methane from the atmosphere (e.g. OH radicals), and inventories estimates anthropogenic emissions based on socio-economic statistics (bottom-up approaches).
Despite significant efforts over the last decades, there are still significant uncertainties in the spatial and temporal quantification of methane sources and sinks. The Global Methane Budget (GMB), under the umbrella of the Global Carbon Project, aims to releases regular synthesis of the methane budget at global and region scales.
This presentation will present the well-known facts, the quite-knowns sources and sinks and their uncertainties, the remaining large uncertainties on the methane budget and its changes over the past decades based on the latest Global Methane Budget activities, and will discussion the not-well knowns and unknows in the methane biogeochemical cycles, including the question of the contribution of the forest ecosystem.
How to cite: Saunois, M.: The Global Methane Budget: the knowns and unknowns, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17309, https://doi.org/10.5194/egusphere-egu26-17309, 2026.
Natural wetlands account for approximately one-third of global methane (CH₄) emissions, while northern peatlands store more than 20% of terrestrial carbon. Environmental change has the potential to enhance microbial decomposition of peat, mobilizing long-stored carbon as CO₂ or CH₄. However, predicting future peatland trace gas fluxes remains challenging due to limited mechanistic understanding and a lack of long-term, ecosystem-scale experimental data for model evaluation. The Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment addresses this gap by providing a rare, whole-ecosystem manipulation of warming and elevated CO₂ in an ombrotrophic forested bog in northern Minnesota.
Here, we measured radiocarbon (¹⁴C) and stable carbon (¹³C) isotopic signatures of surface-emitted CH₄ and CO₂ at the onset of experimental treatments and after five and seven years of combined warming and elevated CO₂. Across treatments, CH₄ emissions were on average approximately a decade older than co-emitted CO₂, indicating differences in carbon source age and processing between the two gases. Despite this age offset, surface carbon fluxes were dominated by recently fixed photosynthates rather than older peat-derived carbon. This finding is consistent with previous work at SPRUCE demonstrating rapid incorporation of newly fixed carbon into dissolved organic carbon pools throughout the peat profile.
In plots exposed to elevated CO₂, isotopic signatures of both ¹⁴C and ¹³C in chamber air were depleted relative to ambient conditions. Correspondingly, surface-emitted CH₄ and CO₂ from elevated CO₂ plots exhibited depleted isotopic values compared to non-elevated plots, reflecting rapid transfer of newly assimilated carbon from vegetation to atmospheric fluxes. Peat sampled four years after the initiation of elevated CO₂ treatments also showed depletion in carbon isotopic values within shallow peat layers relative to ambient CO₂ plots, further supporting enhanced incorporation of recent photosynthates into near-surface peat carbon pools.
Unexpectedly, we found little evidence for increased decomposition or mobilization of older peat carbon, even under conditions that would typically favor peat degradation. Warming treatments, combined with episodically dry conditions, resulted in significant lowering of the water table and measurable loss of surface elevation over the course of the experiment. Despite these physical changes, isotopic evidence did not support substantial contributions of deep or old peat carbon to surface CO₂ or CH₄ emissions.
Together, our results indicate that elevated surface CH₄ and CO₂ fluxes observed under warming at SPRUCE are primarily fueled by rapidly cycling carbon recently fixed by bog vegetation, rather than by accelerated decomposition of long-stored peat carbon. These findings underscore the importance of hydrologic and biogeochemical interactions in regulating peatland carbon dynamics and have critical implications for interpreting experimental manipulations, improving process-based wetland models, and extrapolating peatland responses to climate change across boreal ecosystems.
How to cite: Hedgpeth, A., Mcfarlane, K., McNicol, G., and Hanson, P.: Radiocarbon and Stable Isotopic Signatures Reveal Accelerated Carbon Cycling in a Boreal Peatland Subjected to Warming and Elevated CO2, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2469, https://doi.org/10.5194/egusphere-egu26-2469, 2026.
Mineral soil forest floors often act as net methane (CH4) sinks. The contribution of the different components of the forest floor, such as soil, shrubs, mosses and their roots and the roots of trees, to the sink and the factors affecting their contribution are not well known. Predicting the CH4 flux dynamics of forests requires understanding the component fluxes and drivers, such as microbial population, soil moisture and temperature, and composition and coverage of the forest floor vegetation.
The CH4 exchange of the forest floor at the SMEAR II experimental forest in central Finland (Hari & Kulmala, 2005) was monitored using manual and automated chambers for a total of more than 10 years (2006-2016 manually, 2021-mid 2023 and mid 2025 onwards automatically). In addition, a manipulation experiment was conducted using manual chambers where either tree, shrub or mycorrhizal roots were excluded by trenching. Also, the effect of above ground vegetation (shrubs, mosses) on CH4 flux dynamics was studied. The humus and soil layers next to the automated chambers were inspected for presence of methanotrophs.
We found that the forest floor is a persistent sink for CH4 through the year, CH4 being consumed even during winter on all measurement plots. The general trend in the long-term measurements was towards a larger sink during growing season. Increasing soil temperature increased the sink during the growing season, while soil moisture decreased it. During growing season, a diurnal pattern was observed where higher CH4 consumption occurred during night time.
In the trenching experiment the exclusion of tree, shrub or mycorrhizal roots did not affect soil CH4 uptake, however, the cutting all above ground vegetation increase CH4 uptake compared to presence of normal vegetation (shrubs and mosses). Based on the probe-targeted metagenomic sequencing, methanotrophic bacteria within the organic and mineral soil layers consisted mainly of alphaproteobacterial high-affinity oxidizers, including taxa potentially adapted to oxygen-limited conditions.
Hari, P., & Kulmala, M. (2005). Station for Measuring Ecosystem-Atmosphere Relations (SMEAR II). Boreal Environment Research, 10(5), 315-322.
How to cite: Koskinen, M., Polvinen, T., Putkinen, A., Vainio, E., Ryhti-Laine, K., Rantanen, S., Loponen, M., Schiestl-Aalto, P., Kolari, P., Siljanen, H., and Pihlatie, M.: Persistent and increasing forest floor methane consumption in a boreal mineral-soil pine forest over seasons and years, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16952, https://doi.org/10.5194/egusphere-egu26-16952, 2026.
Abandoned peat extraction areas are significant hotspots of major greenhouse gas (GHG) emissions, including CO2, CH4, and N2O, compared to drained or undisturbed peatlands. These areas are subject to restoration through either rewetting or afforestation. However, the long-term successional dynamics of GHG fluxes and the underlying microbial mechanisms remain poorly understood. We present GHG flux monthly dynamics and related microbial functional gene abundances across four different-aged afforested sites in Estonia sampled from 2023 to 2025: a young plantation (YP; 1-3 yrs) of Silver birch (SB), Scots pine (SP), Norway spruce (NS), Black alder (BA), and a reference area without trees, a mid-age plantation (MP; 17 yrs) of SB, SP, NS and a reference area, an older plantation (OP-SB, 30 yrs), and a natural riparian forest (NF-BA, ~80 yrs) on a river bank.
In YP, all tree species showed excellent growth in the first three years, particularly silver birch, which demonstrated that this species is highly suitable for the afforestation of abandoned peat extraction areas. In YP and MP plantations, soil CO2 emissions were higher in areas with trees than in the reference area without trees, which was possibly caused by additional autotrophic respiration and the addition of fresh, easily decomposable carbon from tree roots. On the temporal scale, CO2 fluxes increased significantly across YP, OP-SB, and NF-BA during the latter part of the study period, yet remained stable in MP. Methane dynamics were strongly influenced by stand age and species; the oldest forest (NF-BA) consistently acted as a CH4 sink (mean, -31.6 ± 2.7 µg C m− 2 h− 1), supported by the higher oxygen content in river water and the highest abundance of pmoA-containing methanotrophs. Due to intensive precipitation and increasing soil water content (SWC), the older birch plantation (OP-SB) transitioned from a minor to a major CH4 source (23.8 ± 9.61 µg C m− 2 h− 1), while all young plantations remained persistent sources (75.6 ± 17.1 - 85 ± 8.25 µg C m− 2 h− 1). This was due to the elevated water table in YP throughout the entire study period. Across all sites, CH4 fluxes negatively correlated with pmoA abundance, highlighting the critical role of aerobic methanotrophic potential in peat soils.
Nitrous oxide emissions were highest in the old alder forest (NF-BA, 13.7 ± 2 µg N m− 2 h− 1), followed by mid-age plantation (MP, 8.92 ± 1.14 µg N m− 2 h− 1), which were particularly high during freeze-thaw cycles and post-precipitation periods. Overall, N2O fluxes showed a positive correlation with SWC. In the riparian Black alder forest, N2O fluxes were negatively correlated with the C: NO3- ratio and positively linked to a high abundance of all Nitrogen-cycling functional genes and soil NO3- levels. Random forest modeling identified total Carbon, SWC, and nirK gene proportions as the primary predictors of N2O emissions.
These findings demonstrate that while afforestation of abandoned peat extraction areas can eventually establish CH4 sinks in peatlands, the tree species and stand age significantly modulate the net radiative forcing of the restored ecosystem through altered N-cycling and microbial community structures.
How to cite: Kazmi, F. A., Masta, M., Espenberg, M., Pärn, J., Thayamkottu, S., and Mander, Ü.: Impact of afforestation on GHG fluxes and related microbiome in abandoned peat extraction areas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4992, https://doi.org/10.5194/egusphere-egu26-4992, 2026.
Aerated soils, especially forest soils, are a sink for atmospheric methane, oxidizing an average of 30 to 40 Tg (bottom-up and top-down estimates) of this powerful greenhouse gas each year. Methane-oxidizing microorganisms, i.e., methanotrophs, mediate this methane sink. Soil methane uptake (SMU) depends primarily on environmental factors, such as soil water content and temperature. Climate change is expected to alter these soil properties, affecting SMU, but more research is needed to understand how SMU will respond to combined changes in temperature and precipitation.
To investigate how soil water content and temperature interact to regulate SMU and methanotroph abundance, we established a rain exclusion experiment in an upland forest soil on the Telegrafenberg campus, Potsdam (Germany), and began monitoring SMU and microbial community composition and abundance at the 0-10 cm soil depth. Soil methane uptake is measured biweekly using a chamber-based method, while microbial abundances are assessed monthly by qPCR (pmoA, mcrA, and 16S rRNA gene) and 16S rRNA gene sequencing. Additionally, we measured methane uptake and microbial gene abundances of soil samples from the same location in controlled laboratory incubations at varying water contents and temperatures.
The incubation experiment revealed that SMU was highest at 35% and 65% of the maximum water-holding capacity. The incubations with 100 and 130% WHC even switched to methane production. The community composition shifted along the moisture gradient and differed significantly across water levels. Regarding the methane-cycling community, there was an increase in Methylocystis, Methanobacteria and Methanocella, and in the high-water content treatments. The community composition of methanotrophs was dominated by Methylocapsa and Methylocella. The differences in methane uptake were accompanied by differences in the abundances of microbial genes (mcrA and pmoA). So far, all forest plots show high methane uptake, and the methanotroph community is dominated by type II methanotrophs. Our research will provide valuable insights into how climate change may impact SMU and the associated microbial community in upland forest soils.
How to cite: Täumer, J., Schaffer, O., Kitte, A., and Liebner, S.: Interactive effects of soil moisture and temperature on methane uptake and microbial community dynamics in an upland forest soil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16812, https://doi.org/10.5194/egusphere-egu26-16812, 2026.
Riparian zone soils are being applied as nature-based solutions for treating wastewater treatment plant effluents via intermittent horizontal subsurface flow systems. While their treatment efficiency is well documented, their role in greenhouse gas (GHG) dynamics, particularly emissions mediated through tree stems, remains largely unexplored. This study quantified tree stem and soil emissions of CO2, CH4, and N2O within an innovative riparian-zone wastewater treatment system and evaluated the influence of hydrological conditions, soil properties, and tree species. From April to October 2023, treated wastewater was applied in alternating wet and dry cycles of one week each, with five sampling campaigns per condition. GHG fluxes were measured from soils (N = 15) and from tree stems at approximately 0.5 m height (N = 18). Concurrently, soil temperature, moisture, pH, and carbon and nitrogen content were assessed. The dominant tree species included Alnus glutinosa, Ulmus minor, Fraxinus excelsior, and the non-native Platanus × hispanica. Soil GHG emissions were primarily driven by environmental conditions. Soil CO2 emissions were mainly controlled by temperature, whereas soil CH4 and N2O were ruled by groundwater table fluctuations. Soil N2O emissions increased under shallower water tables and higher soil temperature and moisture. Soil CH4 fluxes were spatially heterogeneous, with higher emissions in areas where groundwater table was shallower. Overall, the intermittent wet/dry management supported both soil GHG production and consumption without causing a substantial net increase in emissions.Tree stem emissions were strongly species-dependent and often exceeded soil CO2 and CH4 emissions, while N2O emissions were almost negligible. Platanus × hispanica consistently showed the highest stem emissions across all gases, emitting approximately threefold more CO2 and over two orders of magnitude more CH4 than soils. Ulmus minor and Alnus glutinosa also exhibited elevated stem CH4 emissions compared to soils (20 and 9 times higher, respectively), whereas stem N2O emissions were generally about half of soil emissions for all species. Notably, Fraxinus excelsior frequently acted as a sink for N2O. Stem CO2 emissions increased with soil temperature and nitrogen content and peaked during the warmest months but were not influenced by hydrological conditions. In contrast, CH4 emissions displayed a significant interaction between species and wet conditions, suggesting transport of CH4 produced in deeper soil layers through stems or in situ microbial production. N2O fluxes from stems were highly variable, with both emissions and uptake observed, indicating control by microscale and potentially internal stem processes.This study provides the first simultaneous assessment of soil and tree stem GHG emissions in a nature-based wastewater treatment system. The results demonstrate that tree species identity is a critical determinant of stem-mediated GHG fluxes and highlight the need to incorporate vegetation structure, particularly tree stems, into GHG budgets and the design of riparian wastewater treatment systems.
How to cite: Poblador, S., Escarmena, L., Izquierdo, A., Mattana, S., Ribas, A., Roca, N., and Sabater, F.: Tree stems dominate methane but not nitrous oxide emissions in a riparian nature-based wastewater treatment system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23183, https://doi.org/10.5194/egusphere-egu26-23183, 2026.
Methane (CH4) is a potent greenhouse gas, yet the role of trees in the global CH4 budget remains uncertain. While some studies report CH4 emissions from wetland and certain upland trees via soil-derived transport or in-tree production, others suggest that upland forests may function as net atmospheric CH4 sinks. In this study, we investigated CH4 exchange in an oak savanna in California (AmeriFlux site US-Ton) using a multi-scale measurement approach. From August 2024 till October 2025, we have conducted biweekly measurements of stem CH4 and CO2 fluxes on six mature oak trees at three heights (0.4, 1.3, and 2.6 m), alongside soil CH4 flux measurements near each tree using LI-COR 7810 analyzers and a Smart Chamber. Ecosystem-scale CO2 and CH4 fluxes were quantified using eddy covariance with open-path LI-COR 7500 and 7700 analyzers. To assess sub-canopy flux variability, an additional eddy covariance system was deployed below the canopy. Tree surface area for flux upscaling was quantified using terrestrial laser scanning. Tree stems generally acted as small CH4 sources throughout the year, whereas soils consistently functioned as minor CH4 sinks, especially in sun-exposed areas. Stem vertical stem flux profiles did not indicate a direct coupling with soil CH4 dynamics. However, during early spring flooding events, the stem bases of some trees emitted episodically large CH4 fluxes, suggesting that transport of soil-derived CH4, in addition to internal production, can contribute to stem emissions. Ecosystem-scale eddy covariance measurements showed no persistent seasonal pattern in CH4 emissions, although modest increases were observed from spring. At the annual scale, sub-canopy eddy covariance CH4 fluxes were comparable to soil chamber-based estimates, indicating that the under-canopy the soil likely functions as a small CH4 sink. In contrast, above-canopy eddy covariance measurements indicated that the ecosystem as a whole is a small net CH4 source. This discrepancy may be explained by non-microbial CH4 production from oak leaves, supported by incubation experiments and the pronounced increase in ecosystem CH4 fluxes following leaf emergence.
How to cite: Kasak, K., Ranniku, R., Beland, M., Verfaillie, J., and Baldocchi, D.: Methane Flux Dynamics in a California Oak Savanna, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2623, https://doi.org/10.5194/egusphere-egu26-2623, 2026.
Our knowledge of how greenhouse gas (GHG) fluxes vary from the soil to the tree canopy is limited, particularly in upland tropical rainforests. In this case study, we show changes in the fluxes of the primary GHGs (carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O)) along the soil - stem continuum, and their relationships with corresponding stem traits at different heights. To do this, we used static chambers to measure the GHG fluxes from three stems, both on the surrounding forest floor and at eight heights ranging from 0.5 m to 30 m, while also assessing tree traits at these heights. We selected representative emergent trees from a tropical forest in French Guiana, South America. We found no clear pattern in the GHG fluxes along the stems, with highly variable CO₂ emissions and alternating CH4 and N2O emissions and uptake. Regression analysis showed that stem traits related to the tree’s surface area, bark, and sapwood partly explain the measured fluxes along the stem height. For CO₂ fluxes, the best explanatory variables are identified as bark surface temperature, bark water content, and sapwood density; for CH₄ fluxes, the key drivers are tree diameter, bark water content, and bark surface temperature; and for N₂O fluxes, the more influential variables are sapwood density, and sapwood water content. We concluded that the variability in GHG fluxes along the stems was not only specific to tree traits, but also to individual trees. These findings pose a challenge for scaling efforts - it will not be trivial to create bottom-up estimates of tree-impacted fluxes, and a convergence of approaches will be needed to generate a complete GHG balance for these ecosystems.
How to cite: Khatiwada, K. R., Janssens, I. A., Richter, A., Runkle, B., Stahl, C., and Bréchet, L. M.: Testing vertical influences on greenhouse gases fluxes (CO2, CH4 and N2O) along tropical tree stems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6055, https://doi.org/10.5194/egusphere-egu26-6055, 2026.
Tropical forests occupy a substantial share of the Earth’s forested land area. In addition to serving as major carbon reservoirs, these ecosystems influence the global greenhouse gas (GHG) balance by acting both as sinks and sources of methane (CH₄) and nitrous oxide (N₂O). Despite their importance, and sensitivity to climate change, the biogeochemical functioning of tropical forests remains insufficiently understood, particularly with respect to processes occurring in above-ground vegetation.
In this study, we investigated GHG cycling in tree canopies at two peat-swamp forest sites in the Peruvian Amazon: a protected palm swamp reserve Quistococha (3.83417° S, 73.31889° W) and a nearby secondary peatland forest Zungarococha, which served as a reference system.
Field campaigns conducted in November 2023 and May 2024 quantified potential CH₄ and N₂O production and uptake in leaves and twigs of three to four representative tree species (Symphonia globulifera, Mauritia flexuosa, Hevea sp., Tabebuia sp.). Aerobic incubations were performed on-site over 48 hours, with daily gas sampling for analysis via gas chromatography. Biological nitrogen fixation was assessed using 15N isotope labeling over a 72-hour incubation. In parallel, branch material was collected for metagenomic characterization of epiphytic and endophytic microbial communities.
Across all tree species, leaves exhibited small but statistically significant fluxes of both CH₄ and N₂O. In contrast, twig samples displayed species-specific behavior: Hevea sp. acted as a weak sink for both gases, whereas Symphonia globulifera was a consisted source. Considerable variability was observed not only among species but also between the two forest sites within the same species. Nitrogen fixation activity was detected in three of the four studied taxa. Metagenomic analyses revealed the genetic capacity for complete denitrification pathways and for N₂ fixation, while genes associated with nitrification (amoA) were rare. All analyzed tree species contained a high diversity of methanotrophic bacteria. Reads related to methanogenic archaea suggested presence of variable CH4 production pathways.
Our findings highlight tropical tree canopies as active components in the GHG cycling. By linking gas fluxes with the microbial functional potential, this work provides new insights into how above-ground plant–microbe interactions can shape ecosystem-level GHG balance in tropical peatland forests.
How to cite: Putkinen, A., Tenhovirta, S., Gyða Gunnlaugsdóttir, E., Kohl, L., Espenberg, M., Mander, Ü., and Pihlatie, M.: Methane and nitrogen cycling within the tropical tree canopies in the Peruvian Amazon wetlands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20187, https://doi.org/10.5194/egusphere-egu26-20187, 2026.
In parts of the northern boreal zone, a significant number of peatlands have previously been drained for forestry. Climate change is increasing the frequency of forest fires, making these peatland forests particularly vulnerable to wildfires due to thick organic layers and low water table levels. Peatlands store approximately 10% of global soil nitrogen (N) and peatland forests in particular may act as a source of nitrous oxide (N2O), which is a potent greenhouse gas contributing to ozone depletion. Although forest fires affect several factors influencing soil N dynamics, very little is known about the impact of wildfires on the N cycle and N2O emissions on burned peatland sites. We investigated these impacts with a peat column experiment by simulating forest fire conditions with controlled burning.
We collected peat profiles up to 50 cm depth from three different undrained and drained peatland sites in Southern Finland in May 2025 (n=50). Peat columns were incubated outdoors for three months, and half of the columns were scorched in mid-summer with a gas torch to simulate a surface fire. During the experiment period, N2O, carbon dioxide (CO2), and methane (CH4) were measured weekly. After three months, incubated columns were dissected, and peat samples were collected to analyze soil physicochemical parameters, microbial community structure, and the quality of soil organic matter.
Preliminary results suggest that nutrient-rich peatland forests act as N2O sources under favorable conditions for N2O production, while nutrient-poor sites are negligible as N2O sources. The fire appeared to shift these patterns and temporarily increase N2O emissions across peatland types. Further analyses will evaluate how post-fire changes in different peat N pools relate to observed N₂O flux dynamics.
How to cite: Hakkola, S., Teikari, J., Korkiakoski, M., Pihlatie, M., Polvinen, T., and Aaltonen, H.: Fire-driven shifts in nitrous oxide emissions in boreal peatland soils , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10870, https://doi.org/10.5194/egusphere-egu26-10870, 2026.
Methane (CH4) is a potent greenhouse gas, and microorganisms play a crucial role in its cycling. While soil microbial processes are well studied, the microbial basis of CH4 production and oxidation within tree tissues remains poorly understood. Trees play an active role in forest CH4 exchange, yet studies on tree-associated microbial contributions are only beginning to emerge. In this study, we aimed to assess the abundance of CH4-cycling genes in shoots (leaves and terminal branches) and wood cores of four tree categories: European beech (Fagus sylvatica), European hornbeam (Carpinus betulus), birch (Betula pendula and Betula pubescens), and Norway spruce (Picea abies) along a transect spanning temperate to subarctic regions. We assessed CH4 exchange through shoot incubation experiments and measured internal CH4 concentrations in stem wood. Targeted metagenomic approach was used to analyze the relative abundance of CH4-cycling genes. Our study revealed that among shoots, birch, spruce and beech showed potential CH4 emissions, while hornbeam indicated potential CH4 consumption in the incubation study. Beech had the highest internal stem wood CH4 concentration, and hornbeam the lowest when compared to the ambient concentration. Metagenomic analysis confirmed the presence of key methanogen and methanotroph genes in both tissues. Soluble CH4 monooxygenase gene (mmoX) were most abundant in birch shoots and spruce shoots. In addition, CH4 exchanges showed strong positive correlation with shoot ammonia, whereas CH4 concentration on stem wood showed strong positive association with particulate CH4 monooxygenase (pmoA) and methanogen-to-methanotroph gene ratio. These findings provide new insights into tree microbiome and its contribution to CH4 exchange in forest ecosystem.
How to cite: Thiyagarasaiyar, K., Paul, D., kerttula, J., Keski-Karhu, M., Soosaar, K., Mander, Ü., Machacova, K., Pumpanen, J., and Siljanen, H.: Methane Exchange and Microbial Functional Potential in Forest Tree Tissues, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4387, https://doi.org/10.5194/egusphere-egu26-4387, 2026.
Nitrous oxide (N2O) is a strong greenhouse gas with the capacity of depleting ozone layer. Nitrous oxide is naturally produced in nitrogen cycle by microbial processes, but anthropogenic activities have increased the emissions to the atmosphere. Agricultural soil management and excessive use of nitrogen fertilizers are the main reason for increased emissions. Nitrous oxide reductase (nosZ) is a key gene required for the reduction of N2O and the consumption of it through microbial processes.
The aim of this work was to observe the effects of increased concentration of N2O to the activation on nosZ genes in microbes from leaf samples. The samples from labelling experiment enabled detecting, whether 15N-N2O labelling affected the nitrogen isotope ratio of the plant tissues. The quantitative analysis of nosZ and 16S rRNA genes was used to evaluate the transcription and activity of the genes. The composition of the microbial population of nosZ genes was determined from data obtained from amplicon sequencing with Illumina Miseq using bioinformatic analysing.
The results showed that amplification of clade I was successful in most of the samples, and there was moderate positive correlation between transcription of clade I and nitrogen fixation to the biomass. Clade II amplified only in one sample. Sequencing analyses revealed a wide range of microbial species with nosZ clade I gene, including species associated with nitrogen fixation.
How to cite: Siljanen, H., Kerttula, J., Thiyagarasaiyar, K., Paul, D., Keski-Karhu, M., Soosaar, K., Mander, Ü., Machacova, K., and Kohl, L.: Active microbial nitrous oxide consumption captures nitrogen for plant tissues , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18971, https://doi.org/10.5194/egusphere-egu26-18971, 2026.
Methane (CH4) is a potent greenhouse gas and the second most important contributor to the Earth’s warming after carbon dioxide (CO2). Atmospheric methane concentrations have nearly tripled since pre-industrial times, exceeding 1,930 ppb in 2025, and its radiative forcing is approximately 28-30 times greater than that of CO2 over a 100-year time scale. As a result, methane is at the centre of the climate agenda, led by the Global Methane Pledge (GMP) launched at COP26. Owing to its relatively short atmospheric lifespan ranging from 7 to 12 years, methane concentration is highly sensitive to changes in the balance between its sources and sinks.
Soils have long been recognised as the primary terrestrial methane sink alongside atmospheric oxidation. However, recent observations suggest that trees growing in free-draining soils may constitute an overlooked and potentially significant methane sink. Despite its possible importance, the magnitude, drivers, and global relevance of this tree-mediated methane uptake remain poorly constrained, introducing substantial uncertainty into current methane budget estimates. This knowledge gap is particularly pronounced in temperate forests, where evidence of tree methane uptake is limited to only two tree species (Fraxinus excelsior and Acer pseudoplatanus), leaving the broader sink potential of these ecosystems largely unexplored.
Here, we present preliminary results on spatial and temporal variability of stem methane fluxes measured across multiple UK native and non-native tree species in newly planted forests under contrasting forest management approaches, including monoculture and mixed-species woodlands. This experiment is conducted at the Norbury Park Estate, Shropshire (central England), close to the Birmingham Institute of Forest Research (BIFoR) FACE facility. These data will provide new insights into potential drivers of tree-mediated methane uptake in temperate forests and help assess the additional climate benefits of forest expansion under different planting strategies.
How to cite: Rabbai, A., Ordoñez, A., Barba, J., Robinson, A., Dryburgh, A., and Gauci, V.: Hidden Figures: how tree species shape methane uptake in temperate forests., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5842, https://doi.org/10.5194/egusphere-egu26-5842, 2026.
Trees are known to emit and consume methane (CH4) and nitrous oxide (N2O), important greenhouse gases (GHGs). Most studies have focused on stems, whereas the role of tree leaves in forest CH4 and N2O exchange remains unknown. In recent decades, forests have been responding to changing environmental conditions, including increasing/elevated atmospheric carbon dioxide (eCO2). However, the long-term effect of eCO2 on tree CH4 and N2O exchange is almost unknown.
We suggested that the conserved stomatal behavior under eCO2 may directly affect N2O and CH4 fluxes from leaves or stems by altering transpiration, carbon assimilation and allocation, and indirectly soil N2O and CH4 fluxes by altering soil moisture and root exudation patterns.
At the Birmingham Institute of Forest Research’s Free Air CO2 Enrichment (BIFoR-FACE) facility, we studied i) CH4, N2O and CO2 exchange from soils, and stems and shoots of mature Common Hazel (Corylus avellana), and ii) the long-term effect of eCO2 on this GHG exchange. The facility dominated by English Oak with sub-canopy hazel includes three arrays with +150 ppm CO2 enrichment above the ambient (eCO2) and three arrays under ambient CO2 (aCO2).
We measured GHG exchange from three hazel trees and three soil positions in each array and in one sunny aCO2 plot in June 2025. Hazel trees at all arrays grow under low photosynthetically active radiation (PAR). Photosynthesis and transpiration were measured in parallel to GHG fluxes at all studied trees. The gas exchange was studied using static chamber systems and portable LiCOR analysers.
The soil was a sink for CH4 and a source for N2O and CO2. The nine years of eCO2 enrichment tended to reduce the soil CH4 uptake by 55%, and significantly increased soil N2O and CO2 emissions by 93 and 62%, respectively. The stem emissions of CH4, N2O and CO2 were not affected by eCO2. However, trees growing under sunny conditions showed significantly higher stem CO2 efflux than shaded trees. The shoots were CH4 sources irrespective of eCO2 treatment. The shoots turned from being an N2O source under aCO2 to a weak N2O sink under eCO2 (non-significant change). The leaves exposed to eCO2 showed higher CO2 assimilation and transpiration rates compared to aCO2. However, the leaves growing under sunny ambient conditions demonstrated much higher physiological activity than leaves under shaded ambient conditions. The eCO2 seems to partly compensate the low PAR intensities at arrays, and approximates the light curve to the sunny leaves.
Concluded, eCO2 seems to affect the GHG fluxes from soils rather than from hazel stems and shoots. The tree CO2 exchange tends to be more related to PAR conditions than to the atmospheric CO2 levels, mainly due to shaded conditions at arrays.
Acknowledgement
This research was supported by the Ministry of Education, Youth and Sports of CR within programs LU-INTER-EXCELLENCE II [LUC23162] and CzeCOS [LM2023048], and project AdAgriF-Advanced methods of greenhouse gases emission reduction and sequestration in agriculture and forest landscape for climate change mitigation [CZ.02.01.01/00/22_008/0004635]. We thank Robert Grzesik and Kris Hart from BIFoR-FACE for all their field support.
How to cite: Machacova, K., Klem, K., Medňanský, T., Warlo, H., and Ullah, S.: Effect of elevated atmospheric CO2 concentration on greenhouse gas exchange of common hazel trees and soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2737, https://doi.org/10.5194/egusphere-egu26-2737, 2026.
There is substantial uncertainty regarding how different components of mature forests respond to rising atmospheric CO₂ concentrations under ongoing climate change. Tree stems, in particular, may act as increased carbon sinks due to enhanced growth under CO₂ fertilization, but they may also release more CO₂ as a consequence of higher metabolic rates and accelerated carbon cycling. Here, we investigated stem CO₂ fluxes in a mature oak (Quercus robur) stand exposed to elevated CO₂ since 2016 as part of a Free-Air CO₂ Enrichment experiment (BIFoR FACE, UK; +150 ppm above ambient concentrations). Stem CO₂ fluxes were measured over one year through monthly campaigns at 1.3 m height, and seasonally along the stem profile up to 4 m height. Stem CO₂ fluxes exhibited a pronounced seasonal pattern, with higher rates during the growing season, a decline in autumn, and consistently low fluxes during winter. However, neither the magnitude nor the seasonal dynamics of stem CO₂ fluxes were affected by elevated CO₂. Furthermore, partitioning total stem fluxes into maintenance respiration (associated with the metabolism of living stem tissues) and growth respiration (associated with the biosynthesis of new stem cells) revealed no significant response of either component to elevated CO₂. Stem CO₂ fluxes also showed no consistent vertical gradient along the stem, and this pattern was similarly unaffected by CO₂ enrichment. Overall, these findings indicate a strong functional resilience of stem CO₂ fluxes in mature trees to elevated atmospheric CO₂. This resilience may have important implications for predicting forest carbon balance responses to future climate conditions, particularly in mature temperate forests.
How to cite: Barba, J., Rabbai, A., Salomon, R., Curioni, G., and Gauci, V.: Strong resilience of stem CO2 fluxes from a mature temperate forest under elevated atmospheric CO2, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22270, https://doi.org/10.5194/egusphere-egu26-22270, 2026.
European beech (Fagus sylvatica L.) is a both native and extensively cultivated species found in Central and Southeast Europe's upland forests. These beech forests soils are known to emit nitrous oxide (N₂O), sequester methane (CH₄), and release carbon dioxide (CO₂), individually influenced by specific site conditions. The interplay of nitrogen (N) and carbon cycling, along with greenhouse gas (GHG) turnover in these forests, is affected by N deposition, but the long-term effects of N-deposition on GHG exchange involving soil and mature trees are not well understood.
We examined how simulated increased N-deposition affects GHG emissions and soil N-composition in a pre-alpine eutrophic beech forest in Northeastern Italy, subjected to high N-addition. Since 2015, the site has undergone N-manipulation involving four treatments with three replicates: control (N0, ambient N-deposition), above canopy N-addition (N30A, 30 kg/ha*yr N), and soil N-addition at 30 and 60 kg/ha*yr, respectively (N30 and N60). For this study, one plot for each treatment was considered. In September 2023, we measured N₂O, CH₄, and CO₂ fluxes from stems and accompanying soil, and analyzed soil samples for biological and physico-chemical properties.
Beech stems acted as net CH₄ sinks and CO₂ sources, with limited N₂O exchange, unaffected by nine years of artificial N-treatment. Similarly, soil CO₂ emissions remained unchanged, but soil CH₄ uptake increased by 40% in N30 and N60 plots. Conversely, N-treated plots showed significantly lower soil N₂O emissions than controls (nearly 50-fold difference). High flux variability suggests that the observed effects cannot be solely ascribed to N-treatment, likely due to the influence of complex micro-topography.
Soil analyses revealed that N-addition strongly affected soil chemistry, and microbial functional diversity. Control plots maintained higher concentrations of nitrate, nitrite, and total dissolved inorganic nitrogen, indicating enhanced N-consumption or transformation rates under elevated inputs. The N-addition reorganized the microbial community, marked by increased richness and evenness and a shift towards reductive processes, confirmed by the enrichment of genes associated with assimilatory and dissimilatory nitrate reduction and denitrification. Furthermore, carbon cycle responses included increased methanotrophic capacity in N60, evidenced by pmoA gene enrichment, while this effect was absent in canopy-applied treatments.
Overall, while long-term N-addition did not significantly alter GHG stem fluxes, it facilitated greater soil CH₄ uptake through increased microbial methane oxidation capacities and caused substantial restructuring of microbial communities with increased N-reduction potential.
This research was supported by the Ministry of Education, Youth and Sports of CR within the programs LU-INTER-EXCELLENCE II [LUC23162] and CzeCOS [LM2023048], project AdAgriF-Advanced methods of greenhouse gases emission reduction and sequestration in agriculture and forest landscape for climate change mitigation [CZ.02.01.01/00/22_008/0004635], and by the Spanish Government grants PID2024-162617NB-I00 funded by MCIN, AEI/10.13039/ 501100011033 EU Next Generation EU/PRTR
How to cite: Schindler, T., Lopez-Sanchez, C., Mattana, S., Warlo, H., Guerrieri, R., Ribas, A., and Machacova, K.: Long-Term Nitrogen Addition Reshapes Methane and Nitrous Oxide Fluxes and Microbial Functional Potential in European Beech Forest Soil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8335, https://doi.org/10.5194/egusphere-egu26-8335, 2026.
Atmospheric methane (CH4) concentrations are rising globally, and evidence suggests natural sources may be responsible. Forests represent the largest terrestrial sink in the global CH4 budget, however CH4 emissions from certain forest ecosystems – wet woodlands (i.e. forested wetlands) – remain poorly constrained. Due to their hydrology, the anoxic soils in wet woodlands provide suitable conditions for methanogenesis. Little is known about the spatial or temporal patterns of CH4 flux in these ecosystems, and the environmental variables that drive these, due to insufficient understanding of biogeochemical mechanisms and limited observations.
To address this, we used hourly-resolved automatic chambers, complimented by a greater expanse of monthly manual chambers to compare CH4 and carbon dioxide (CO2) flux to soil parameters in a temperate wet woodland (Wakehurst, Sussex, UK). From observations over two years, we show that soil temperature is the dominant control of CH4 flux from the wet woodland soil once within high soil moisture (>40%) or water table depth (WTD) (< 0.2m); at lower moisture, changes in WTD and moisture determine CH4 flux. Large seasonal variations were present, where CH4 emissions peaked in summer months (44.05 ±1.15 nmolm-2s-1 (mean)), and reduced in winter (7.54 ± 0.078 nmolm-2s-1 (mean)), with measurements in drier soil moving from source to sink. A diurnal cycle in CH4 flux positively correlated with soil temperature was revealed, with diurnal and seasonal variation comparable in magnitude, highlighting the importance of high temporal resolution flux measurements. Diurnal cycles changed significantly on the hottest days (>90th percentile soil temperature), with diurnal amplitudes of CH4 higher (~100 ppb) than the general trend (~20 ppb).
The large spatial, seasonal and diurnal variability in methane flux we report are significant for quantifying and understanding CH4 emissions from these small fragmented forest ecosystems, which are currently highly uncertain or missing in model estimates. The relationship to soil temperature suggests rising summer temperatures may lead to an increase in summer CH4 emissions in future climate scenarios, and highlights the importance of constraining and understanding this ecosystem within the global CH4 budget.
How to cite: Batten, S., Egan, G., Lee, M., Fisher, R., Milner, A., Wilkes, P., Davidson, S., and Lowry, D.: Constraining temporal and spatial variations of methane flux in a temperate wet woodland , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13079, https://doi.org/10.5194/egusphere-egu26-13079, 2026.
Living trees in forests emit or consume methane (CH4) and nitrous oxide (N2O) through their stems. These stem fluxes can originate directly from the internal tissues, or co-occur from soils and stems. However, the magnitudes, origins, and biogeochemical pathways of these fluxes remain poorly understood.
In our study, we aimed to investigate whether tropical forest habitats (upland versus seasonally flooded areas), tree species and composition of the microbial communities living in the sapwood influence the stem fluxes of CH4 and N2O.
To address this, we measured the in situ CH4 and N2O fluxes in the stems of thirteen tropical tree species using static chambers. We investigated the microbial communities in the sapwood by sequencing the 16S rDNA of bacteria and archaea on an Illumina MiSeq platform. Measurements were taken in two contrasting habitats: well-drained, nutrient-poor soil in an upland area, and waterlogged, nutrient-rich soil in a seasonally flooded area of a tropical forest in French Guiana. Fluxes, woody tissue microbial communities, and related tree traits were measured during the wet season.
Overall, we observed a significant effect of forest habitat on sapwood microbial communities, which remained relatively consistent within specific tree species. Stem fluxes per unit of stem surface area were approximately 2.5 times higher for CH4 and lower for N2O in the seasonally flooded forest, compared to the upland forest. Variability in these fluxes was observed not only between the two forest habitats, but also among and within tree species. Surprisingly, methanotrophs and methanotrophs were barely detectable, and denitrifiers and nitrifiers were also scarce in the stem tissues, despite the high CH4 and, to a lesser extent, N2O emissions measured on the stem surfaces. This suggests that, in our site, CH4 and N2O fluxes mainly result from processes occurring in the heartwood, bark, soil, or a combination of these. Further research is needed to shed light on the microbial mechanisms underlying the exchange of CH4 and N2O between the trees and the atmosphere in tropical forest ecosystems.
How to cite: Bréchet, L., Stahl, C., Le Noir de Carlan, C., Richter, A., Bonal, D., Janssens, I., and Verbruggen, E.: Tree species and forest habitat shape stem methane and nitrous oxide fluxes and sapwood microbial communities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22794, https://doi.org/10.5194/egusphere-egu26-22794, 2026.
Tropical ecosystems are major contributors to global methane (CH₄) emissions, yet substantial uncertainties remain in both top-down and bottom-up estimates. Such uncertainties partly can be attributed to limited understanding of various emissions and uptake pathways in tropical ecosystem. Most field measurement of CH4 focused solely on soil-atmosphere exchange, overlooking other exchange pathways. Furthermore, several studies from natural forest ecosystem confirmed significant CH4 emission from tree stems. However, such quantification remains scarce in tropical forest plantations, which constitute significant proportion of current land use. A better quantitative and process-based understanding of CH4 emissions, removals, and transport pathways is therefore essential for improving regional and global CH4 budgets and mitigation strategies, especially under changing climate and land use.
In this study, we measured soil and stem CH4 fluxes from two managed plantation forests (Acacia and Eucalyptus plantations) and two natural forests ecosystem (peat swamp forests and riparian forests) in Sumatra, Indonesia. We used LI-8200-01S (LICOR, USA) for soil and semi-rigid chambers made with polyethylene terephthalate (PET) plastic sheets for stem measurements. We used LI-7810 (LICOR, USA), connected to the chambers during the measurement period to measure the CH4 concentration. The fluxes were calculated using a linear function of changes in CH4 concentration during incubation time.
The preliminary result shows that plantation emits significantly smaller CH4 from both soil and stem compared to respective natural forested ecosystems, indicating that land-use change substantially alter the methane production, consumption, and transport processes. We observed a clear decreasing stem CH4 fluxes with increasing stem height in both ecosystems on peat, strongly suggest a soil-originated CH4 transport mechanism. Interestingly, no significant difference between stem height was detected in Eucalyptus plantations and adjacent riparian forests. Tree stems acted as net CH4 sources across all ecosystems. Soil surfaces functioned as CH4 sources in peatland ecosystems but as net CH4 sinks in Eucalyptus plantations and adjacent riparian forests. These results demonstrate strong contrasts in soil–stem CH4 dynamics between peatland and non-peatland ecosystems in tropics. Comprehensive, pathway-specific assessments are therefore required to reduce uncertainties in tropical CH4 budgets.
How to cite: Gunawan, S., Nurholis, N., Nardi, N., Susanto, A. P., Ramadhanti, S., Kusumawardhani, S. D., Wenadi, R., Samosir, A. G. A., Jurgen, K. Y., Rohayani, P., Jabbar, A., Pertiwi, N., Kurnianto, S., Gauci, V., Barba, J., Agus, F., and Deshmukh, C. S.: Multi-pathway methane and nitrous oxide emissions from Acacia plantations on tropical peatlands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8685, https://doi.org/10.5194/egusphere-egu26-8685, 2026.
The fluxes of different greenhouse gas (GHG) species have long been studied using a variety of techniques, with the choice of method largely determined by the measurement scale. Small-scale fluxes such as soil chamber measurements may be made using closed transient approaches, whereas direct micrometeorological measurement of ecosystem-scale fluxes predominantly employs eddy covariance or related methodologies. However, methods to directly quantify plant-mediated fluxes at the leaf scale remain limited.
Increasingly, plant-mediated transport (PMT) and plant-mediated exchange (PME) are recognised as important, and in some ecosystems even dominant pathways by which some soil-produced GHGs reach the atmosphere. These processes are influenced by both biotic and abiotic factors, and physiological characteristics of the plant, such as stomatal conductance, are thought to play a significant role. However, a limited body of literature constrains our understanding of this component of GHG flux, largely due to the lack of appropriate instrumentation and methodologies to quantify these fluxes. Clipping studies have been used to remove vegetation from plots and monitor net changes in flux, but this precludes investigation of interactions between plant physiology and the GHG flux.
Plant physiological responses are typically measured in an open flow through system to minimise perturbation of physiology. Portable photosynthesis systems measure CO2 and H2O concentrations before and after interacting with the leaf. The differences between these concentrations (ΔCO2, ΔH2O) permit calculation of physiological parameters including net CO2 assimilation (A), intercellular CO2 concentration (Ci), and stomatal conductance to water vapour (gsw) while the chamber is continuously refreshed with stable air, allowing the maintenance of the leaf in a steady physiological state.
However, the open flow-through nature of the photosynthesis system has traditionally made quantification of plant-mediated trace gas fluxes, such as CH4 and N2O, challenging. The surface area of plant material enclosed is typically small, and the relatively small changes in trace gas concentrations require a high degree of precision to resolve. Additional complexity arises from the large differences in H2O concentration before and after interaction with the leaf due to transpiration. Most systems also show a sensitivity to changing CO2 concentration, which is commonly utilised in plant physiology measurements.
Here we describe and characterise a system that integrates trace gas measurements with a commercial photosynthesis system (LI-COR LI-6800), managing water transients and integrating data from the various gas analysers, including real-time on-board flux calculations. Presented are two commercial OF-CEAS trace gas analysers, measuring CH4 and N2O (LI-COR LI-7810 and LI-7820 respectively). We examine the impact of averaging interval on measurement precision for a range of CO2 mole fractions and assess the dependence of trace gas mole fraction to changing CO2 mole fractions. We also present a sensitivity analysis for zero trace gas flux.
How to cite: Smillie, I., Bachle, S., Lynch, D., Vath, R., and Hupp, J.: Integrating leaf-level CH₄ and N₂O measurements with a field-portable photosynthesis system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5594, https://doi.org/10.5194/egusphere-egu26-5594, 2026.
