PeatlandN2O - N2O Budgets in Peatlands – from Process to Ecosystem

Selle kollektsiooni püsiv URIhttps://hdl.handle.net/10062/120548

The ground-breaking nature of the PeatlandN2O (N2O Budgets in Peatlands – from Process to Ecosystem) project lies in the integrated use of a combination of innovative methods, yielding a pioneering synthesis and modeling of nitrous oxide fluxes (N2O) at various spatial scales, linked to microbial processes. The Project will:
1. determine the role of rapidly changing environmental factors such as soil moisture, freeze-thaw, and canopy effectson N2O emission, particularly in hot spots and hot moments;
2. distinguish between and quantify key N2O production and consumption processes using labelled nitrogen, isotopologues, and microbiome structure;
3. integrate results of experiments and novel measurement techniques (automated chambers, stationary and mobile eddy covariance towers, canopy profile analysis) into the PEATN2O model of N2O fluxes and related environmental factors to enable the prediction of hot spots and hot moments of N2O emissions;
4. upgrade IPCC emission factors and suitable land-use strategies to mitigate N2O emissions in peatlands, also considering other greenhouse gases;
5. predict the global distribution of N2O emissions according to the land use and five climate change scenarios for a 100-year time horizon.

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Nüüd näidatakse 1 - 20 32

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Impact of drainage on soil CH4 and N2O fluxes in nutrient-rich hemiboreal peatland forests of Europe
(2026) Kamil-Sardar, Muhammad; Laiho, Raija; Jauhiainen, Jyrki; Butlers, Aldis; Schindler, Thomas; Vahter, Hanna; Čiuldienė, Dovilė; Vigricas, Egidijus; Teemusk, Alar; Kull, Ain; Lazdiņš, Andis; Haberl, Andreas; Bārdule, Arta; Līcīte, Ieva; Samariks, Valters; Mander, Ülo; Armolaitis, Kęstutis; Soosaar, Kaido
Background and aims Peatland forests play a significant, yet highly variable, role in atmospheric methane (CH4) and nitrous oxide (N2O) emissions. Drainage reduces CH4 but increases N2O fluxes from nutrient-rich soils, creating complex climate trade-offs. To refine regional climate strategies, a clearer understanding of soil fluxes and influencing factors across forest types in the hemiboreal zone is needed. Methods This study presents two years of soil flux and environmental data collected from 2020 to 2023 using manual chambers at 18 drained (DF) and 7 undrained (UF) sites, with different tree species, in Estonia, Latvia, and Lithuania. Results Soil water‑table depth was the primary control on annual CH4 exchange; DF sites acted as CH4 sinks (–4.6 kg ha–1 y–1), whereas UF sites were net sources (38.2 kg ha–1 y–1). In contrast, N2O emissions occurred at all sites, averaging 5.9 kg ha–1 y–1 in DF and 1.4 kg ha–1 y–1 in UF soils. Within DF sites, Myrtillus‑type pine stands exhibited the lowest N2O fluxes, while alder stands showed the highest, followed by birch- and spruce-dominated stands, reflecting differences in hydrology, pH, and C/N ratios of the soil. Conclusions Our findings reveal significantly lower CH4 and moderately higher N2O emissions from DF soils than the IPCC Tier 1 temperate zone emission factor (EF), which has thus far been used for the hemiboreal zone. This study can improve national GHG inventories using specific information. We recommend applying Baltic region-specific EFs, as the mean annual CH4 and N2O emissions showed no significant difference across the three countries.
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Transitional hypoxia during peatland water table fluctuations drives high N2O fluxes via shifting microbial pathways
(Volume 305, Part 1, 2026) Masta, Mohit; Ali Kazmi, Fahad; Espenberg, Mikk; Visnapuu, Triinu; Sennett, Louise B.; Eving, Lauri; Lewicka-Szczebak, Dominika; Deb, Sushmita; Khanongnuch, Ramita; Kuusemets, Laura; Kupper, Priit; Butterbach-Bahl, Klaus; Mander, Ülo
Nitrogen (N) cycling in peatlands is sensitive to variations in water table, temperature, and soil moisture. Water table fluctuations in peatlands can trigger the formation of transitional oxic and hypoxic zones within the peat and influence N2O fluxes. However, studies exploring these transitions by combining isotopic and microbial analyses are rare. This study assessed the impact of oxic-to-hypoxic transitions on N dynamics in drained peat soil. Birch-planted mesocosms were treated with 15N-NO3- and 15N-NH4+ tracers, while artificial fog generation allowed for the quantification of N2O exchange between the soil surface and the atmosphere. Rewetting reduced soil oxygen levels, significantly increasing N2O fluxes; peak value (162 ± 22.80 μg N m−2 h−1) was recorded under hypoxic conditions. During the transition, the abundance of nirK-type denitrifiers increased. N2O was initially enriched by the 15N-NH4+ tracer, followed by the 15N-NO3- tracer, which contributed significantly to the N2O flux under hypoxic conditions. The 3D FRAME isotope model attributed early N2O production to nitrification (Ni) and nitrifier denitrification (nD); however, it identified a dual contribution from nitrification (Ni) and bacterial denitrification (bD) during the later phases. NosZ genes were detected in birch leaf samples, suggesting a potential aboveground microbial N2O sink. 15N tracer also confirmed the solubility of soil N2O in fog droplets during the experimental period, but the fraction of dissolved N2O was found to be very low (<0.2%). Nonetheless, these findings warrant further research.
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Genetic Potential for N₂O Metabolism in Tree Tissues: Insights From Nitrogen Cycling Gene Prevalence and nosZ Diversity Across Tree Species
(2026) Thiyagarasaiyar, Krishnapriya; Paul, Dhiraj; Kerttula, Johanna; Keski-Karhu, Milja; Soosaar, Kaido; Mander, Ülo; Hallin, Sara; Machacova, Katerina; Pumpanen, Jukka; Siljanen, Henri M.P.
Nitrous oxide (N2O) is a potent greenhouse gas, and microorganisms play a crucial role in its metabolism. While N2O cycling among soil microorganisms is well studied, there is a major knowledge gap regarding the distribution and diversity of these microorganisms within tree ecosystems. In this study, we aimed to comprehensively assess the potential for nitrogen (N) cycling and the diversity of N2O-reducing microorganisms in shoots (leaves and terminal branches) and wood cores of four tree species — European beech (Fagus sylvatica), European hornbeam (Carpinus betulus), birch (Betula pendula and Betula pubescens) and Norway spruce (Picea abies). We assessed N2O exchange through shoot incubation experiments and measured internal N2O concentrations in stem wood. Inorganic N species were studied as indicators of microbial transformation, and a targeted metagenomic approach was used to determine the relative abundance of N-cycling genes and nosZ clade I and II diversity. Our study revealed that hornbeam shoots showed potential N2O emissions (0.002–0.007 ng N2O g⁻¹ FW h⁻¹), while beech shoots indicated N2O consumption (-0.001 to -0.017 ng N2O g⁻¹ FW h⁻¹). Birch had internal stem wood N2O concentration of + 150.39 ppb, and beech − 9.74 ppb when compared to the ambient concentration. Targeted metagenomic analysis revealed the presence of key nitrification and denitrification genes in both tissue types. In particular, nosZ genes were detected in shoots (0 to 26.48 per 100,000 reads) and in wood cores (0 to 31.95 per 100,000 reads), with clade I dominating over clade II and Rhizobiales prevalent within clade I. Overall, our findings show that internal tree tissues harbour distinct N‑cycling microbial assemblages dominated by nosZ clade I, suggesting that trees may function as localized N2O sinks or sources depending on tissue type and microbial composition.
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National-scale geospatial modelling of recommended riparian buffer widths
(2026) Uuemaa, Evelyn; Kmoch, Alexander; Kull, Ain; Mõisja, Kiira; Tominga, Hanna-Ingrid; Guamán-Pintado, Pamela; Mander, Ülo
Determining optimal riparian buffer widths, especially considering landscape spatial heterogeneity, is challenging, often relying on computationally intensive hydrological models with limited scalability. Empirical nomographs, linking terrain, soil, and slope, offer a more tractable alternative. Building upon a nomograph developed for Estonian catchments in the earlier research, we present its first computational implementation within a geospatial modelling framework. We developed a geospatial modelling algorithm in Python to calculate recommended buffer widths based on slope, specific slope length (synthesised from flow length, slope length, and LS factor), and soil type, utilising high-resolution national datasets. This algorithm was applied to the entire territory of Estonia (approx. 43,000 km2). The model produces spatially explicit buffer width recommendations that reflect local variations in topography and soil conditions. The proposed framework provides a computationally efficient and scalable tool for supporting strategic planning, policy development, and prioritisation of riparian buffer implementation. While not intended for direct site-level design, it offers a robust first-order assessment of spatial patterns in buffer width requirements and can be further refined through local calibration and validation.
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Linking nitrogen transformations and soil δ15N to assess drivers of nitrogen losses across a tropical peat swamp forest and an oil palm plantation
(2026) Wangari, Elizabeth Gachibu; Yung Teo, Kien; Mwanake, Ricky Mwangada; Sangok, Faustina Elfrida; Lindang, Herman Umbau; Chaddy, Auldry; Lau, Sharon Yu Ling; Khan, Fawad; Busman, Nur Azima; Lo, Kim San; Vahter, Hanna; Kamil-Sardar, Muhammad; Kanger, Kärt; Willibald, Georg; Ambus, Per; Pihlatie, Mari; Soosaar, Kaido; Espenberg, Mikk; Butterbach-Bahl, Klaus; Kiese, Ralf; Mander, Ülo; Melling, Lulie
Conversion of tropical peatland forests to oil palm plantations has been associated with elevated nitrous oxide (N2O) emissions and nitrate (NO3−) leaching, yet the biogeochemical mechanisms driving these nitrogen (N) losses remain poorly understood. To address this gap, soil N2O fluxes, gross N transformation rates, microbial gene abundances, annual NO3− leaching rates, and bulk soil δ15N signatures were quantified along transects in Malaysia that included intact tropical peat swamp forest and drained oil palm plantation. Oil palm plantation sites had higher topsoil oxygen (O2) concentrations than forest sites, indicating that drainage shifts soils from predominantly anaerobic to aerobic conditions. These redox shifts, together with fertilizer inputs, increased nitrifier gene abundances and enhanced gross nitrification rates, which exceeded ammonification rates by up to 186%, promoting soil NO3− accumulation. The elevated soil NO3− concentrations stimulated N2O production, probably through coupled nitrification-denitrification, and increased NO3− leaching. Overall, these results showed that oil palm plantation sites had higher gaseous and hydrological N losses than peat forest sites. Additionally, nitrification rates, hydrological N export, and gaseous N losses were positively correlated with more enriched bulk soil δ15N values along the land use gradient. These findings demonstrated that bulk soil δ15N patterns may have the potential to serve as indicators of long-term N cycling and losses in tropical peatlands associated with human-induced land use changes.
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Long-term carbon sequestration and heatwave resilience in an old hemiboreal upland coniferous forest
(2026) Rogozin, Svyatoslav; Krasnova, Alisa; Mander, Ülo; Uri, Veiko; Soosaar, Kaido
Boreal forests play an important role in the global carbon cycle due to their extensive area and ability to sequester a considerable amount of atmospheric carbon dioxide (CO2). They are generally stable ecosystems that function as carbon sinks. However, their sink capacity is vulnerable to the impact of extreme weather conditions. In this study, we aim to investigate the multi-year and seasonal carbon dynamics of an old upland coniferous forest in the hemiboreal zone, identify the main environmental drivers influencing annual NEP, and explore the potential legacy effects of the 2018 heatwave. Over an eight-year period (2016–2023), the forest shifted from a carbon sink (mean net ecosystem productivity (NEP) of 238 ± 52 g C m−2 year−1) to a carbon-neutral state in 2020 (NEP = -2 ± 5 g C m−2 year−1) and back to a net carbon sink (NEP = 136 ± 50 g C m−2 year−1). The average NEP over the eight-year period was 170 ± 42 g C m−2 year−1. Our research showed no significant year-to-year changes in GEP during the study period, while the changes in Reco were substantial. Our results confirm that air temperature has the greatest influence on annual NEP. The warmest autumn over the past 19 years, recorded in 2020, and an atypical June together resulted in a noticeable increase in ecosystem respiration, which shifted annual NEP towards negative net values, while no significant impact on GEP was found. Additionally, our study found that the old upland hemiboreal forest showed no legacy effect in the years following the 2018 heatwave, demonstrating its resilience to extreme temperature events. Our results underscore the importance of continuous monitoring carbon dynamics variability to determine the ecosystem's resilience to seasonal temperature fluctuations and to inform management strategies for forests preservation.
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Carbon dioxide dynamics across three stages of tropical peatland conversion to oil palm plantations
(2026) Kiew, Frankie; Hirata, Ryuichi; Hirano, Takashi; Wong, Guan Xhuan; Waili, Joseph Wenceslaus; Lo, Kim San; Soosaar, Kaido; Kasak, Kuno; Melling, Lulie; Mander, Ülo
This study represents the first long-term investigation spanning from a tropical peat swamp forest (PSF) to its conversion into an oil palm plantation (OPP), offering valuable data for assessing carbon dioxide (CO2) dynamics across different conversion stages. The conversion of tropical peat swamp forests to oil palm plantations has significant implications for CO2 dynamics. However, ecosystem-scale studies investigating CO2 dynamics across different stages of land conversion are lacking. This study used the eddy covariance (EC) technique to measure the net ecosystem exchange (NEE) of CO2 above a tropical peat swamp forest in Sarawak, Malaysia, from 2011 until it was cleared in 2017 and ultimately converted into an OPP in 2018. Our study found that the removal of forest biomass during land preparation led to a substantial increase in annual NEE from 25 ± 179 (2011 to 2016) to 2732 ± 655 g C m−2 year−1 (2017 to 2019). This increase was attributed to an 83 % reduction in gross primary productivity (GPP) and a 14 % reduction in ecosystem respiration (Reco). The near-ground environmental conditions also significantly changed across the conversion stages, inducing drier conditions compared to the forest. These changes were found to affect the controlling factors of nighttime NEE during conversion, resulting in a negative relationship with both air temperature and vapor pressure deficit above canopy, in contrast to the typical relationship with groundwater level observed before conversion. The conversion is also found to cause significant reduction in overall ecosystem photosynthetic activity as evidenced by the reduction in maximum gross photosynthetic rate (Pmax), photosynthetic photon flux density (PPFD), quantum yeild (α), and dark respiration (REd). Although ecosystem-scale assessments of CO2 dynamics provide insights into how ecosystems respond to changes in relation to land conversion, it is crucial to assess other respiration components, such as soil respiration and aboveground woody debris, for a more comprehensive analysis.
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Impact of land conversion on environmental conditions and methane emissions from a tropical peatland
(2025) Wong, Guan Xhuan; Hirata, Ryuichi; Hirano, Takashi; Kiew, Frankie; Waili, Joseph Wenceslaus; Mander, Ülo; Soosaar, Kaido; Melling, Lulie
Tropical peatlands are significant sources of methane (CH₄), but their contribution to the global CH₄ budget remains poorly quantified due to the lack of long-term, continuous and high-frequency flux measurements. To address this gap, we measured net ecosystem CH4 exchange (NEE-CH4) using eddy covariance technique throughout the conversion of a tropical peat swamp forest to an oil palm plantation. This encompassed the periods before, during and after conversion periods from 2014 to 2020, during which substantial environmental shifts were observed. Draining the peatland substantially lowered mean monthly groundwater levels from −20.0 ± 14.2 cm before conversion to −102.3 ± 31.6 cm during conversion and increased slightly to −96.5 ± 19.3 cm after conversion. Forest removal increased mean monthly soil temperature by 2.3 to 3.1 °C, reducing net radiation (Rn) and raising vapor pressure deficit (VPD). Following the tree removal, controlled burning temporarily warmed air temperature by 8 °C, increased VPD and significantly attenuated Rn, resulting in negative values owing to radiation interception by smoke and increased surface warming. Contrary to expectations that drainage would lower CH4 emissions, the site remained a consistent net source, with even higher emissions observed during and after conversion. The mean monthly NEE-CH4 during conversion (23.3 ± 8.6 mg C m−2 d−1) was about 2-times higher than before conversion (12.1 ± 5.3 mg C m−2 d−1) and about 1.5-times higher than after conversion (16.3 ± 4.1 mg C m−2 d−1). The heightened CH4 release is likely attributable to emissions from drainage ditches, underscoring their significant role in post-conversion CH4 dynamics. Despite its short duration, controlled burning substantially elevated NEE-CH4, ranging from 0.04 to 0.91 mg C m−2 s−1. Our findings highlight the substantial impact of land conversion on peatland CH4 dynamics, emphasizing the need for accurate flux measurements across various conversion stages to refine global CH4 budgets.
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Dual controls of vapour pressure deficit and soil moisture on photosynthesis in a restored temperate bog
(2025) Thayamkottu, Sandeep; Masta, Mohit; Skeeter, June; Pärn, Jaan; Knox, Sara H.; Smallman, T. Luke; Mander, Ülo
Despite only covering ~3 % of the land mass, peatlands store more carbon (C) per unit area than any other ecosystem. This is due to the discrepancy between C fixed by the plants (Gross primary productivity (GPP)) and decomposition. However, this C is vulnerable to frequent, severe droughts and changes in the peatland microclimate. Plants play a vital role in ecosystem C dynamics under drought by mediating water loss to the atmosphere (surface water vapour conductance) and GPP by the presence/absence of stomatal regulation. This is dependent on soil moisture, air temperature, and vapour pressure deficit (VPD). Although there is ample evidence of the role of VPD on stomatal regulation and GPP, the impact of soil moisture is still debated. We addressed this knowledge gap by investigating the role of bulk surface conductance of water vapour in shifts between climatic (Air temperature (Tair), incoming shortwave radiation (SWR) and VPD) and water limitation of GPP in a peat bog in Canada. A causal analysis process was used to investigate how environmental factors influenced GPP. The results suggested that stomatal regulation in response to increased VPD caused the reduction in GPP in 2016 (~2.5 gC m−2 day−1 as opposed to ~3 gC m−2 day−1 in 2018). In contrast, GPP was limited again in 2019 due to the dry surface. This was driven by the relaxed stomatal regulation adopted by the ecosystem following the initial drought to maximise C assimilation. We found the threshold at which surface water decline limited GPP was at about −8 cm water table depth (82.5 % soil moisture). The causal inference corroborated our findings. The temporal variations of water and energy limitation seen in this study could increasingly restrict GPP due to the projected climate warming.
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Springtime soil and tree stem greenhouse gas fluxes and the related soil microbiome pattern in a drained peatland forest
(2025) Soosaar, Kaido; Ranniku, Reti; Espenberg, Mikk; Truupõld, Joosep; Escuer-Gatius, Jordi; Mander, Ülo
Spring can be a critical time of year for stem and soil methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) emissions as soil freeze–thaw events can be hot moments of gas release. Greenhouse gas fluxes from soil, Downy birch (Betula pubescens) and Norway spruce (Picea abies) stems were quantified using chamber systems and gas analysers in spring 2023 in a northern drained peatland forest. Dissolved gas concentrations in birch sap and soil water, environmental parameters, soil chemistry, and functional gene abundances in the soil were determined. During spring, initially low soil and stem CH4, N2O, and CO2 emissions increased towards late April. Temperature emerged as the primary driver of soil and stem fluxes, alongside photosynthetically active radiation influencing stem fluxes. Soil hydrologic conditions had minimal short-term impact. No clear evidence linked stem CH4 emissions to birch sap gas concentrations, while relationships existed for CO2. Functional gene abundances of the N and CH4-cycles changed between measurement days. Potential for methanogenesis and complete denitrification was higher under elevated soil water content, shifting to methanotrophy and incomplete denitrification as the study progressed. However, our results highlight the need for further analysis of relationships between microbial cycles and GHG fluxes under different environmental conditions, including identifying soil microbial processes in soil layers where tree roots absorb water.
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Soil moisture and microbiome explain greenhouse gas exchange in global peatlands
(2025) Pärn, Jaan; Espenberg, Mikk; Kasak, Kuno; Mander, Ülo; Thayamkottu, Sandeep; Öpik, Maarja; Bahram, Mohammad; Tedersoo, Leho; Davison, John Alexander; Maddison, Martin; Niinemets, Ülo; Ostonen, Ivika; Soosaar, Kaido; Sohar, Kristina; Zobel, Martin
Earth’s climate is tightly connected to carbon and nitrogen exchange between the atmosphere and ecosystems. Wet peatland ecosystems take up carbon dioxide in plants and accumulate organic carbon in soil but release methane. Man-made drainage releases carbon dioxide and nitrous oxide from peat soils. Carbon and nitrous gas exchange and their relationships with environmental conditions are poorly understood. Here, we show that open peatlands in both their wet and dry extremes are greenhouse gas sinks while peat carbon/nitrogen ratios are high and prokaryotic (bacterial and archaeal) abundances are low. Conversely, peatlands with moderate soil moisture levels emit carbon dioxide and nitrous oxide, while prokaryotic abundances are high. The results challenge the current assumption of a uniform effect of drainage on greenhouse gas emissions and show that the peat microbiome of greenhouse-gas sources differs fundamentally from sinks.
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Importance of N2O in greenhouse gas budgets of tropical peatlands
(2025) Pärn, Jaan; Espenberg, Mikk; Soosaar, Kaido; Kasak, Kuno; Thayamkottu, Sandeep; Schindler, Thomas; Ranniku, Reti; Sohar, Kristina; Malaverri, Lizardo Fachín; Melling, Lulie; Mander, Ülo
Tropical peatland ecosystems significantly influence Earth’s climate through their greenhouse gas exchange. Permanently wet peatlands take up carbon dioxide in plants and accumulate organic carbon in soil but release methane. Man-made drainage of peat releases carbon dioxide and nitrous oxide. Exchange of the greenhouse gases in relationship with tropical conditions are poorly understood. This is a global-scale field study of fluxes of three greenhouse gases – carbon dioxide, methane and nitrous oxide – and their environmental drivers across the full moisture range of tropical peatlands. We show that net emission of carbon dioxide dominates greenhouse gas budgets in drained tropical peatlands while nitrous oxide emission is the second most important contributor. Tropical peat swamp forests in their natural wet states are large greenhouse gas sinks and should be a global conservation and restoration priority.
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Temporal dynamics of soil microbial C and N cycles with GHG fluxes in the transition from tropical peatland forest to oil palm plantation
(2025) Midot, Frazer; Goh, Kian Mau; Liew, Kok Jun; Lau, Sharon Yu Ling; Espenberg, Mikk; Mander, Ülo; Melling, Lulie
Tropical peatlands significantly influence local and global carbon and nitrogen cycles, yet they face growing pressure from anthropogenic activities. Land use changes, such as peatland forests conversion to oil palm plantations, affect the soil microbiome and greenhouse gas (GHG) emissions. However, the temporal dynamics of microbial community changes and their role as GHG indicators are not well understood. This study examines the dynamics of peat chemistry, soil microbial communities, and GHG emissions from 2016 to 2020 in a logged-over secondary peat swamp forest in Sarawak, Malaysia, which transitioned to an oil palm plantation. This study focuses on changes in genetic composition governing plant litter degradation, methane (CH4), and nitrous oxide (N2O) fluxes. Soil CO2 emission increased (doubling from approximately 200 mg C m−2 h−1), while CH4 emissions decreased (from 200 µg C m−2 h−1 to slightly negative) following land use changes. The N2O emissions in the oil palm plantation reached approximately 1,510 µg N m−2 h−1, significantly higher than previous land uses. The CH4 fluxes were driven by groundwater table, humification levels, and C:N ratio, with Methanomicrobia populations dominating methanogenesis and Methylocystis as the main CH4 oxidizer. The N2O fluxes correlated with groundwater table, total nitrogen, and C:N ratio with dominant nirK-type denitrifiers (13-fold nir to nosZ) and a minor role by nitrification (a threefold increase in amoA) in the plantation. Proteobacteria and Acidobacteria encoding incomplete denitrification genes potentially impact N2O emissions. These findings highlighted complex interactions between microbial communities and environmental factors influencing GHG fluxes in altered tropical peatland ecosystems.
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Human-Impacted Natural Ecosystems Drive Climate Warming
(2025) Mander, Ülo; Pärn, Jaan; Espenberg, Mikk; Peñuelas, Josep
Current greenhouse gas budgets do not account for most indirect anthropogenic impacts. In this perspective, we call for attention to greenhouse gas fluxes from human-impacted natural ecosystems and their mitigation measures. The article highlights the increasing greenhouse gas (GHG) emissions from natural ecosystems, including CO2, CH4, and N2O. These emissions are becoming significant drivers of global warming, surpassing those from fossil fuel combustion. We introduce the concept of “anthro-natural emissions” on the example of peatlands, referring to emissions from natural ecosystems indirectly impacted by human activities. The concept helps bridge the gap between natural and anthropogenic impacts, providing a more comprehensive understanding of GHG emissions. Anthro-natural emissions are expected to rise as climate warming progresses, contributing to the overall GHG balance. Peatlands, which store approximately 30% of the world's soil carbon, are under increasing pressure from climate warming and human activities. The article emphasizes the importance of addressing both natural and human-impacted ecosystems to mitigate climate change effectively. Increasingly frequent droughts are identified as a major threat to global terrestrial ecosystems, particularly wetlands. The drying of wetlands challenges their capacity to act as carbon sinks and alters their roles in climate regulation. The insights provided are essential for developing effective adaptation strategies relying on soil carbon sequestration as a long-term solution against climate warming. According to our study, the proportion of natural, anthro-natural, and directly disturbed peatlands is approximately 40–20–40, and the ratio is increasing towards anthro-natural peatlands. We highlight a change of paradigm for assessing the importance of different GHG sources. Further, it highlights the need for conservation and restoration of peatlands and renaturalization of forest ecosystems.
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Global peatland greenhouse gas dynamics: state of the art, processes, and perspectives
(2025) Mander, Ülo; Espenberg, Mikk; Öpik, Maarja
Natural peatlands regulate greenhouse gas (GHG) fluxes through a permanently high groundwater table, causing carbon dioxide (CO2) assimilation but methane (CH4) emissions due to anaerobic conditions. By contrast, drained and disturbed peatlands are hotspots for CO2 and nitrous oxide (N2O) emissions, while CH4 release is low but high from drainage ditches. Generally, in low-latitude (tropical and subtropical) peatlands, emissions of all GHGs are higher than in high-latitude (temperate, boreal, and Arctic) peatlands. Their inherent dependence on the water regime makes peatlands highly vulnerable to both direct and indirect anthropogenic impacts, including climate change-induced drying, which is creating anthro-natural ecosystems. This paper presents state-of-the-art knowledge on peatland GHG fluxes and their key regulating processes, highlighting approaches to study spatio-temporal dynamics, integrated methods, direct and indirect human impacts, and peatlands' perspectives.
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Interactions of fertilisation and crop productivity in soil nitrogen cycle microbiome and gas emissions
(2025) Kuusemets, Laura; Mander, Ülo; Escuer-Gatius, Jordi; Astover, Alar; Kauer, Karin; Soosaar, Kaido; Espenberg, Mikk
Fertilised soils are a significant source of nitrous oxide (N2O), a highly active greenhouse gas and a stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N2O emissions into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N2O and N2 emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N2O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with an increased mineral N fertilisation rate. Crop type also has a significant impact on soil N2O emissions. Higher N2O emissions were attained with the application of manure in comparison to mineral fertilisation. Manure amendment also increased the number of N cycle genes that are significant in the variations of N2O. The study indicates that N2O emissions were mainly related to nitrification in the soil. Quantification of nitrogen cycle functional genes also showed the potential role of denitrification, comammox (complete ammonia oxidation) and dissimilatory nitrate reduction to ammonium (DNRA) processes as a source of N2O. Our study did not find soil moisture to be significantly linked to N2O emissions. The results of the study provide evidence that, for wheat, a fertilisation rate of 80 kg N ha−1 is closest to the optimal rate for balancing biomass yield and N2O emissions and achieving a high NUE. Sorghum showed good potential for cultivation in temperate climates, as it showed a similar biomass yield compared to the other crop types and fertilisation rates but maintained low N2O emissions and N losses in a mineral N fertilisation rate of 80 kg N ha−1.
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A comprehensive porewater survey of European peatlands reveals sustained elevated phosphorus levels after 10–20 years of rewetting
(2025) Krishnankutty,; Gelbrecht, Jörg; Petersen, Rasmus Jes; Rayner, Dylan; Lau, Maximilian P.; Frank, Stefan; Andersen, Roxane; Pärn, Jaan; Mander, Ülo; Kotowski, Wiktor; Liu, Haojie; Iversen, Bo V.; Heckrath, Goswin; Hansen, Hans C.B.; Hoffmann, Carl C.; Mäenpää, Maarit I.; Goldhammer, Tobias; Kull, Ain; Florea, Adrian-Florin; Zak, Dominik
Rewetting drained peatlands can lead to high nutrient mobilization, increased methane emissions, and a slow re-establishment of peat-forming vegetation. To guide effective restoration and management, understanding the temporal and spatial variability in porewater chemistry is essential. This study surveyed 64 natural and rewetted peatlands across Germany, Poland, Estonia, Sweden, Georgia, and Scotland from 1997 to 2017. A total of 812 anoxic porewater samples were collected using dialysis samplers (0–0.6 m depth). The rewetted fens exhibited a wide range of dissolved substances, spanning orders of magnitude for soluble reactive phosphorus (SRP: 0.1–18.9 mg L−1), ammonium (NH4+-N: 0.1–117.3 mg L−1), and dissolved organic carbon (DOC: 13–313 mg L−1). However, the mean concentrations were significantly higher than those observed in natural fens (p < 0.05). Depth-integrated mobilization rates for nutrients in rewetted fens were, on average, 23 times higher for SRP (1.8 mg P m−2 d-1) and 4.6 times higher for NH4+-N (3.6 mg N m−2 d-1) compared to their natural counterparts (0.1 mg P m−2 d-1 and 0.8 mg N m−2 d-1). Seasonal variation was also evident in rewetted fens densely colonized by helophytes, with SRP concentrations being lower in the growing season. Notably, SRP concentrations remained elevated 10–20 years after rewetting; however, a 50–80 % decrease was observed at sites characterized by comparatively low iron content in the peat (< 20 mg g−1 dry mass). Further investigations should explore how nutrient dynamics evolve over extended rewetting periods in different contexts, including climate change.
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Mature riparian alder forest acts as a strong and consistent carbon sink
(2025) Krasnova, Alisa; Soosaar, Kaido; Rogozin, Svyatoslav; Krasnov, Dmitrii; Mander, Ülo
Alder forests are widespread across the Northern Hemisphere, often occupying riparian zones and enhancing soil fertility through symbiosis with nitrogen-fixing bacteria. Despite their ecological importance, the ecosystem-level carbon and water exchange of alder forests remains poorly studied, particularly under contrasting hydroclimatic conditions. We studied ecosystem carbon and water fluxes over three contrasting years (“wet”, “drought”, “recovery”) in a mature riparian grey alder forest in Estonia. The forest was a strong and consistent net carbon sink with annual net ecosystem exchange (NEE) ranging from −496 to −663 g C m−2 yr−1, gross primary production (GPP) from −1258 to −1420 g C m−2 yr−1, ecosystem respiration (ER) from 595 to 923 g C m−2 yr−1 and evapotranspiration (ET) varied from 194 to 342 kg H2O m−2 yr−1. Moderate soil water saturation (40 %–50 %) enhanced all ecosystem fluxes. In contrast, progressive drought reduced ER, ET, and to a much lesser extent GPP, with elevated EWUE and suppressed canopy conductance indicating strong stomatal regulation to limit water loss while maintaining carbon sequestration. While soil saturation affected canopy conductance, its effect was outweighed by vapour pressure deficit during the drought year, even after soil water availability recovered. We observed a full recovery in the following year, which was supported by favourable temperature and precipitation, although partially suppressed canopy conductance suggested some vulnerability to possible consecutive droughts in the future. Overall, the forest demonstrated drought resilience and high net carbon uptake across contrasting years, underscoring the capacity of riparian alder stands to sustain carbon sequestration under variable hydroclimatic conditions.
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Nitrogen cycling genes abundance in soil and aboveground compartments of tropical peatland cloud forests and a wetland on Réunion Island
(2025) Kazmi, Fahad Ali; Espenberg, Mikk; Mander, Ülo; Ranniku, Reti; Öpik, Maarja; Püssa, Kersti; Soosaar, Kaido; Kasak, Kuno; Masta, Mohit; Ah-Peng, Claudine
Peatland cloud forests, characterized by high altitude and humidity, are among the least-studied tropical ecosystems despite their significance for endemism and the bioavailable nitrogen (N) that can be emitted as N2O. While research has mainly focused on soil, the above-ground microbial N cycle remains largely unexplored. We quantified microbial N cycling genes across ecosystem compartments (soil, canopy soil, tree stems, and leaves) in relation to N2O and N2 fluxes and soil physicochemical properties in two peatland cloud forests and a wetland on Réunion Island. Complete denitrification minimized N2O emissions and increased N2 fluxes in wetland soils. In cloud forest soils, archaeal nitrification primarily produced nitrate (NO3–), while low pH potentially slowed denitrification, resulting in minimal N2O emissions. Soil N-fixers were more abundant in Erica reunionensis-dominated forests than in mixed forests. Tree stems varied between weak N2O sinks and sources, with fluxes unrelated to gene abundances in stems. High prokaryotic and fungal nirK gene abundance in forest canopy soil suggests potential for above-ground denitrification in wet conditions. nosZ-I genes found in forest canopy soil and leaves (E. reunionensis, Alsophila glaucifolia, and Typha domingensis) indicate that plants, including forest canopy, may play a significant role in the reduction of N2O.
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Distinct microbial communities drive methane cycling in below- and above-ground compartments of tropical cloud forests growing on peat
(2025) Kazmi, Fahad Ali; Mander, Ülo; Khanongnuch, Ramita; Öpik, Maarja; Ranniku, Reti; Soosaar, Kaido; Masta, Mohit; Tenhovirta, Salla A. M.; Kasak, Kuno; Ah-Peng, Claudine; Espenberg, Mikk
Cloud forests are unique yet understudied ecosystems regarding CH4 exchange despite their significance in carbon storage. We investigated CH4 fluxes in peat soil and tree stems of two tropical cloud forests on Réunion Island, one featuring Erica reunionensis and the second a mix of E. reunionensis and Alsophila glaucifolia. The study examined microbiomes across below-ground (soil) and above-ground (canopy soil, leaves, and stems) forest compartments. Metagenomics and qPCR analyses targeted key genes in methanogenesis and methanotrophy in soil and above-ground samples, alongside soil physicochemical measurements. CH4 fluxes from peat soil and tree stems were measured using gas chromatography and portable trace gas analyzers. Peat soil in both forests acted as a CH4 sink (− 23.8 ± 4.84 µg C m− 2 h− 1) and CO2 source (55.5 ± 5.51 µg C m− 2 h− 1), with higher CH4 uptake in sites dominated by endemic tree species E. reunionensis. In forest soils, a high abundance of n-DAMO 16 S rRNA gene (3.42 × 107 ± 7 × 106 copies/g dw) was associated with nitrate levels and higher rates of CH4 uptake and CO2 emissions. NC-10 bacteria (0.1–0.3%) were detected in only the Erica forest soil, verrucomicrobial methanotrophs (0.1–3.1%) only in the mixed forest soil, whereas alphaproteobacterial methanotrophs (0.1–3.3%) were present in all soils. Tree stems in both forests were weak sinks of CH4 (-0.94 ± 0.4 µg C m− 2 h− 1). The canopy soil hosted verrucomicrobial methanotrophs (0.1–0.3%). The leaves in both forests exhibited metabolic potential for CH4 production, e.g., exhibiting high mcrA copy numbers (3.5 × 105 ± 2.3 × 105 copies/g dw). However, no CH4-cycling functional genes were detected in the stem core samples. Tropical cloud forest peat soils showed high anaerobic methanotrophy via the n-DAMO process, while aerobic methanotrophs were abundant in canopy soils. Leaves hosted methanotrophs but predominantly methanogens. These results highlight the significant differences between canopy and soil microbiomes in the CH4 cycle, emphasizing the importance of above-ground microbiomes in forest CH4 gas budgets.

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