Orals: Mon, 4 May, 14:00–15:45 | Room 1.31/32
Enhanced ‘woody growth’ (dry matter increments, specifically), averaging 10%, has been sustained in patches of long-established (180+ years old) oak forest through 9 years of treatment with elevated CO2 (eCO2; 150 ppm above ambient). Root exudation of carbon (C) into the rhizosphere increased by 63%, which primed the microbes for nutrient acquisition to meet enhanced tree N demands. A ‘faster-tighter’ nitrogen cycle accelerates the return of nitrogen via ammonification to plant-available forms and suppresses processes such as nitrification. This ecosystem-scale N conservation strategy supports increased net productivity by maintaining the nutritional balance of the trees in the C-rich atmosphere. The faster-tighter N-cycle makes an additional 25 kg N ha-1 yr-1 available to the trees under eCO2. That is, the forest’s N-cycle adjusts to the increased C supply, but whether this capacity to adjust endures may be constrained by soil organic N stocks and anthropogenic N deposition. Further, when considering broader aspects of the forest under eCO2, we find nutritional deficiencies producing a cascade of nascent ecosystem fragility in pollen, seeds, seedlings, and food webs. The clear policy implications are: (i) that enhanced net primary productivity does not, in itself, guarantee forest resilience; (ii) that both C and N emission pathways must be accounted for when forecasting 21st-century C uptake into temperate forests; and (iii) that, when proposing forests as natural climate solutions, understanding C-nutrient interactions is of primary concern.
How to cite: MacKenzie, R., Rumeau, M., Reay, M., Handy, G., Mayoral, C., Gardner, A., Norby, R., Smith, A., Hartley, I. P., Hamilton, R. L., and Ullah, S.: They say “carbon!”, we say “…and nutrients!”: N-cycle biogeochemistry sustaining net productivity in a long-established temperate broadleaf forest under elevated CO2, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12836, https://doi.org/10.5194/egusphere-egu26-12836, 2026.
Human activities have increased atmospheric reactive nitrogen (N) deposition, with important consequences for ecosystem biogeochemical cycles. In forest ecosystems, tree canopies act as active filters that intercept, transform and redistribute atmospheric N before it reaches to the soil. These canopy-level processes determine the chemical forms of N that become available for biological uptake or are transferred to the soil. Despite their importance, the temporal variability of these processes remains poorly understood, particularly in Mediterranean ecosystems with pronounced seasonal contrasts.
In this study, we investigated the seasonal dynamics of atmospheric N transformations within the canopy of a Mediterranean Holm oak forest (Quercus ilex / Q. rotundifolia) in Spain. We focused on canopy-scale nitrification processes and the abundance of N-fixing and nitrifying microorganisms associated with the phyllosphere and precipitation. Canopy N fluxes were quantified, nitrate sources were identified using Δ¹⁷O isotopic signatures, and microbial abundances were quantified by qPCR, to explore seasonal dynamics and their environmental drivers.
Our results show that the canopy acted as a net sink for atmospheric N throughout the year, indicating that N inputs did not exceed ecosystem demand and suggesting potential N limitation. The nitrate measured in throughfall samples indicated a predominantly atmospheric origin during most of the year (76–92%). In contrast, during summer up to 76% of the nitrate was derived from in situ biological processes at canopy level. These enhanced biological transformations were correlated with weather conditions, particularly the higher temperatures and dry conditions typical of summer, which may favour nitrification and promote the accumulation of N compounds on leaf surfaces. Reduced plant activity and lower N uptake during summer further prolong N residence time within the canopy, increasing the likelihood of microbial transformations. Both archaeal and bacterial nitrifiers, as well as N-fixing microorganisms, were detected year-round in the phyllosphere and precipitation. Archaeal nitrifiers consistently outnumbered bacterial ones, and showed a marked increase during summer, driven by higher radiation, temperature and lower humidity. This pattern suggests that archaea may play a significant important role in nitrification, coinciding with the highest nitrification rates observed in summer. These findings highlight the crucial function of canopy processes in regulating N fluxes in Mediterranean forests, particularly during summer. The seasonal dynamics of biological transformations and microbial communities emphasise the influence of environmental conditions on N cycling.
How to cite: Ruiz-Checa, R., Elustondo, D., Ávila, A., Guerrieri, R., Walter, W., Mattana, S., and Alonso, R.: Biological nitrogen transformations within the tree canopy: seasonal variations and microbial contributions to nitrogen fluxes in a Mediterranean Holm oak forest, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20602, https://doi.org/10.5194/egusphere-egu26-20602, 2026.
Temperature sensitivities (Q10) of nitric oxide (NO) and nitrous oxide (N2O) emissions are the core parameters to project future trajectories of soil nitrogen (N) cycling and climate feedback. However, spatial variations in Q10 and their underlying microbial processes are unknown, hindering accurate projection. We sampled 21 upland soils across a 4000-km transect in China and conducted incubations at 5 to 40°C with 15N tracer to quantify Q10 of NO and N2O emissions, alongside process-specific emissions from nitrification, denitrification and co-denitrification. Optimal temperatures (Topt) for these processes exceeded 30°C and increased with mean annual site temperature. Q10 ranged widely from 1.3 to 5.7 (averaged 3.3) and 1.0 to 5.9 (averaged 3.5) for NO and N2O emissions, respectively, showing higher values observed in lower mid-latitudes and high-pH croplands. The Q10 values were governed by shifts in the ratios between nitrifier and denitrifier functional genes, which are in turn regulated by edaphic and climatic factors. Our observed Q10 values are significantly higher than the default of 2 set in Earth System Models (ESMs). Integrating the experiment-derived Q10 values into model projections reveals that current ESMs underestimate future NO and N2O emissions by 17.5–26.6% across the Shared Socioeconomic Pathways (SSP3-7.0 and SSP5-8.5) by 2100. This suggests a substantial underestimation of future gaseous N losses from global croplands under warming.
How to cite: Ba, W., Yu, H., Yu, L., Dörsch, P., Nie, M., Han, P., Hobbie, E., Fang, Y., and Zhou, F.: Substantial underestimation of soil nitrogen gaseous losses from global croplands under warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8694, https://doi.org/10.5194/egusphere-egu26-8694, 2026.
Nitrogen dioxide (NO2) is a critical atmospheric pollutant and ozone precursor, yet biogenic soil sources remain poorly constrained. Current models assume soil NO2 flux is exclusively depositional. Here we demonstrate that soils can produce NO2 through microbial superoxide (O2–) production. Using manipulative slurry experiments, native microbial communities produced 6-10 times more NO2 than sterile controls following NO exposure. Stimulating superoxide production with NADH increased NO2 formation 15-fold, while inhibiting NADH oxidase reduced production to near-sterile levels. Superoxide dismutase decreased NO2 production by 50-75%, and superoxide concentration explained 60% of variation in NO2 production rates. Addition of peroxynitrite to soil increased headspace NO2, confirming this intermediate as the mechanistic link. These findings reveal a novel pathway linking carbon and nitrogen cycling where heterotrophic decomposers facilitate biogenic NO to NO2 via superoxide chemistry, potentially explaining discrepancies between satellite observations and modelled soil NOx emissions.
How to cite: Mushinski, R., Purchase, M., Raff, J., and Wang, D.: Microbial superoxide production influences biogenic nitrogen dioxide formation in soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20705, https://doi.org/10.5194/egusphere-egu26-20705, 2026.
Excessive emissions of greenhouse gases (GHGs), are driving uncontrolled planetary heating. This is already causing devastating consequences for our climate and to avoid the worst consequences of climate change, we mustn’t let global heating exceed 1.5°C.
Nitrous oxide (N2O) is 265 times as powerful a GHG as CO2 and persists in the atmosphere for 120 years, meaning today’s N2O emissions will still be affecting the climate in five generations’ time. Given the ongoing trajectory of global GHG emissions, we already require negative emissions technology to limit global heating to 1.5ºC
Current understanding is that the only process that consumes N2O in soils is complete denitrification, which occurs under extremely wet conditions when a proportion of N2O produced is converted to nitrogen gas and returned to the atmosphere. New technologies, however, have provided data which suggest that there may be a previously unknown biological process which consumes N2O in soils, under dry aerated conditions.
We will present initial data describing soils which have this capacity and discuss approaches to answer the following key questions: how N2O uptake occurs in soils; who is responsible; why these organisms take up N2O; where within the soil N2O uptake occurs; when it occurs and under what conditions and; how much N2O is drawn down.
How to cite: Keane, J. B., Ineson, P., Moir, J., and Hodson, M.: Investigating biological uptake of nitrous oxide (N2O)in soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21533, https://doi.org/10.5194/egusphere-egu26-21533, 2026.
Peatlands are globally significant sinks for carbon and nitrogen. The carbon and nitrogen cycles in peatlands are highly sensitive to changes in water table, temperature, and soil moisture. Long-term rewetting has been suggested as a potential restoration strategy for peatland restoration; however, if done improperly, it can create transitional oxic and hypoxic zones, which can act as major hotspots for N2O emissions. In this study, we investigated the effect of transitioning from oxic to hypoxic conditions in a drained peat soil prepared in mesocosms, which were installed in a climate chamber to simulate day and night conditions. The humidity in the climate chamber was maintained above 90% to study the interaction of the produced N2O with artificial fog, generated using foggers. We prepared 12 mesocosms, out of which 4 received a 15N-NO3- tracer, 4 received a 15N-NH4+ tracer, and the remaining 4 were kept as controls. One birch plant sapling was also planted in each mesocosm before the start of the experiment. Soil oxygen levels were reduced from 9 mg/L to 1.5 mg/L over the course of ten days, and the effects of this change from oxic to hypoxic conditions were studied.
Our results indicate that due to a decrease in soil oxygen over time, N2O emissions increased and peaked on the final day (162 ± 22.80 μg N m-2 h-1) of the experiment. During this transition (oxic to hypoxic), we observed a significant increase in the abundance of nirK-type denitrifiers. Our 15N tracers indicate that on the initial days, the produced N2O was dominated by the 15N-NH4+ tracer, but on the final days, the 15N-NO3- showed a significant contribution to the N2O flux. The birch sapling showed a major uptake of 15N-NO3- in its roots and leaves. This indicates a preference for birch saplings towards the soil nitrate pool compared to the soil ammonium. We also applied the 3D Frame isotope model to the natural isotopomers of soil-produced N2O and observed a change in the N2O production processes over the course of the experiment. The initial days were dominated by nitrifiers’ denitrification and nitrification; however, by the end of the experiment, isotopic mapping revealed the dominance of nitrification, coupled with bacterial and nitrifier denitrification. We also found evidence of the solubility of tracer-produced N2O in the fog water.
Our study demonstrated that the improper restoration of peatlands through rewetting can create transitional oxic-hypoxic zones, which can serve as hotspots for N2O emissions. Moreover, soil-produced N2O can be dissolved in fog during colder seasons, which can be further coupled by tree leaves as they also possess potential for N-cycle processes.
How to cite: Masta, M., Ali Kazmi, F., Espenberg, M., Visnapuu, T., Sennett, L. B., Eving, L., Lewicka-Szczebak, D., Deb, S., Khanongnuch, R., Kuusemets, L., Kupper, P., Butterbach-Bahl, K., and Mander, Ü.: Transitional hypoxia during peatland rewetting drives high N2O fluxes via coupled microbial pathways with evidence of N2O sink potential by fog and tree leaves., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7079, https://doi.org/10.5194/egusphere-egu26-7079, 2026.
Deep meromictic lakes are anoxic below the chemocline and accumulate chemically reduced solutes in bottom waters. In the 120 m deep meromictic Lake Idro (Italy), nitrate is almost completely consumed at the chemocline depth, yet measurable concentrations (≈ 3 μM NO₃⁻) are consistently found in the sulphide-rich bottom water and surficial sediment. Under strongly reducing conditions, nitrate is expected to be rapidly consumed as evidenced by measured denitrification rates, and its presence suggests the existence of a hidden source.
Two potential nitrate sources were hypothesized: (i) the oxidation of NH₄⁺ to NO₃⁻ via manganese oxides (MnOx) as the lake sediment is rich in Mn; and (ii) allochthonous inputs, supported by nitrate-rich sinking particles.
To test the first hypothesis, potential nitrification was measured in sediment slurry incubations amended with ¹⁵NH₄⁺ and MnOx. These experiments showed no clear evidence of NH₄⁺ oxidation, indicating that Mn-driven nitrification is unlikely to sustain the observed nitrate pool. The analyses of intracellular nitrate storage revealed nitrate concentrations an order of magnitude higher than the dissolved fraction, suggesting that sinking diatoms are potential nitrate sources for the benthic system.
Diatoms are well known for their ability to accumulate nitrate in vacuoles and to respire it under unfavourable or anoxic conditions. Lake Idro experiences frequent diatom blooms, and the sediment is enriched in diatom frustules, primarily from the genus Aulacoseira, which is capable of surviving in anoxic sediments for extended periods. These observations support the hypothesis that sinking diatoms may act as carriers of nitrate to the deep sediments of Lake Idro, fuelling benthic nitrogen transformations.
The application of the ¹⁵N isotope-pairing technique on intact sediment cores confirmed active 14N-NO3- denitrification in the monimolimnion sediment, with measured rates of 5.9 ±1.5 µmol 14N-NO3- m-2 h-1, accounting approximately for 25 % of total benthic denitrification in the entire lake. Dissimilative nitrate reduction to ammonium (DNRA) rates were also detected but were five times lower than denitrification. These findings demonstrate that diatom-mediated delivery of intracellular nitrate may represent a quantitatively significant and previously overlooked nitrate source to sediments in stratified lakes. Consequently, this mechanism represents an important sink for nitrate and must be considered in future nitrogen-cycle models of meromictic and stratified lakes.
How to cite: Morini, L., Sudo, M. L., Arroyave-Gomez, D. M., Magri, M., Benelli, S., Marzocchi, U., Castaldelli, G., and Bartoli, M.: Hidden source of nitrate fuel benthic denitrification in the anoxic monimolimnion of a deep meromictic lake., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1371, https://doi.org/10.5194/egusphere-egu26-1371, 2026.
Freeze–thaw cycles (FTCs) are recognized as important regulators of nitrous oxide (N₂O) emissions in temperate and boreal soils, yet the underlying drivers and processes during FTC remain poorly understood.
We set up two controlled incubation experiments to investigate the effect of freezing and thawing on N2O emissions, emission drivers and N2O forming processes. Soil samples were collected during spring freeze-thaw period from a biodiversity cover crop plot trial in Helsinki, southern Finland. In experiment 1, we studied the effects of soil depth and cover crops (CC) on N₂O emissions, soluble nutrients (N, P, C) and active N cycling genes (RNA) during consecutive freezing and thawing phases over a 3-week period. In experiment 2, we studied N2O emissions and their isotopologue ratios in a dynamic automated FTC experiment with alternating freezing (–4 °C) and thawing (+4 °C) cycles. To support the controlled experiments, we conducted twice weekly N2O flux measurements in the field during the spring freezing-thawing period.
Throughout the experiment 1, we found significantly greater N2O production at the surface (0 – 2 cm) compared to the subsurface (9 – 11 cm) soil depth. To support this, soil nitrate, ammonium, total dissolved N, dissolved organic C and soluble reactive P concentrations where higher in the topsoil compared to the subsurface. In experiment 2, N2O emissions occurred during thawing periods but were stimulated by freezing. Based on isotopologue ratios, the N2O originated predominantly from denitrification. Field N2O flux data support the laboratory results showing higher N2O emissions during freeze-thaw, and smaller during warm periods, and that cover crop treatments potentially lead to higher N2O emissions during soil freeze-thaw. Overall, the findings demonstrate the episodic nature of freeze-thaw related N2O emissions governed by substrate dynamics in soil that support conditions suitable for “hot moments”.
How to cite: Pihlatie, M., Virta, O., Aaltonen, H., Teikari, J., Turunen, P., Kohl, L., Znamínko, M., Palacin Lizarbe, C., Nykänen, H., Biasi, C., and Koskinen, M.: Cover crops, soil depth and nutrient dynamics drive N2O emissions and N2O forming processes during soil freezing and thawing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16855, https://doi.org/10.5194/egusphere-egu26-16855, 2026.
Sub-Saharan Africa (SSA) faces a critical dilemma: how to close yield gaps and ensure food security while minimizing agriculture's climate footprint. While nitrogen (N) fertilisation is essential for boosting crop productivity, it can also lead to increased nitrous oxide (N₂O) emissions, thereby further fueling climate change. SSA is highly vulnerable to changes in climate. Yield-scaled N₂O emissions offer a framework to evaluate agricultural climate efficiency, but regional estimates require robust modeling approaches that are calibrated to local conditions. Here, we calibrated LandscapeDNDC, a process-based biogeochemical model, using the most comprehensive dataset on N2O emissions and yields as obtained from 25 field experiments conducted across 12 locations in SSA. These experiments focused on the dominant food crops of maize, sorghum, millet, and rice, and legumes (soybeans and beans). Site-specific parameterization was achieved through Latin hypercube sampling via SPOTPY-LDNDC, followed by validation against an independent dataset of 256 treatment-years across 44 sites representing SSA's major agroecological zones. We assessed the model’s performance in terms of absolute N₂O emissions, yields, and yield-scaled emissions (YSE). We then applied sensitivity analysis to identify the primary drivers of emission variability. Our results show that LandscapeDNDC effectively captures the variability in N₂O and YSE across various cropping systems, highlighting its potential as a tool for national and regional GHG inventories. This could be an efficient way to improve greenhouse gas inventories, enabling better-targeted mitigation and sustainable intensification strategies.
How to cite: Barbacias, M. G., Butterbach-Bahl, K., and Rahimi, J.: Site-Calibrated LandscapeDNDC Modeling of Yield-Scaled N₂O Emissions from Smallholder Cropping Systems in Sub-Saharan Africa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1215, https://doi.org/10.5194/egusphere-egu26-1215, 2026.
Atmospheric wet nitrogen deposition (NDepwet) represents the key pathway through which anthropogenic nitrogen emissions are transferred to terrestrial ecosystems. However, global assessments remain limited by sparse observations and strong regional variability in emissions, atmospheric chemistry, and transport. To overcome these constraints, we developed a global ensemble machine-learning framework to generate annual NDepwet estimates for all terrestrial regions from 2005 to 2019 by integrating satellite-derived reactive nitrogen concentrations, meteorological fields, and data from major ground-based monitoring networks. The model achieved strong predictive performance (R² > 0.8), enabling a consistent reconstruction of global deposition trends.
Globally, NDepwet declined from 61.24 Tg N yr⁻¹ in 2005 to 52.31 Tg N yr⁻¹ in 2019 (−14.6%), driven mainly by reductions in NOₓ emissions. Yet this decline was highly uneven. Developed regions reduced NOₓ emissions by 26% and NH₃ by 5%, but achieved only ~15% reductions in NDepwet , revealing a clear decoupling between emission controls and deposition outcomes. In contrast, developing regions exhibited minimal declines (−3.4% in Africa; −0.6% in India) or slight increases (+0.8% in South America), reflecting continued emission growth and shifts in atmospheric circulation that enhanced cross-boundary nitrogen transport.
Trajectory-derived backward/forward ratios further revealed changes in each region’s role as a net importer or exporter of reactive nitrogen. Africa and India showed sharp decreases in these ratios (Africa: 0.94→0.36; India: 1.16→0.88), indicating a transition toward export-dominated regimes and reduced sensitivity of NDepwet to domestic emissions. Across most regions, only 18–35% of deposition originated from local emissions, implying that long-range transport is the dominant driver of NDepwet.
These findings demonstrate that regional emission controls alone cannot effectively reduce nitrogen deposition when transboundary imports remain high. Effective mitigation will require internationally coordinated emission reductions and targeted support for developing regions where emissions continue to rise.
How to cite: Mohinuddin, S., Huang, J.-C., and Chen, Y. Y.: Uneven decline and role of long-range atmospheric transport of global wet nitrogen deposition , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1717, https://doi.org/10.5194/egusphere-egu26-1717, 2026.
Oxides of Nitrogen (NOx) are key precursors of tropospheric ozone and particulate nitrate (NO3-), both of which contribute to air quality degradation and climate forcing. NOx is oxidized to nitric acid (HNO3), which partitions into particulate NO3-, an important component of PM2.5. The formation of HNO3 and ultimately NO3- occurs through multiple chemical pathways and is influenced by atmospheric chemistry as well as meteorological parameters like temperature, relative humidity, and boundary layer dynamics. India has been recognised a global hotspot for NOx emission, owing to rapid urbanization and population growth. Major sources of NOx include emissions from traffic, agriculture, biomass burning, and combustion. Despite being a major contributor of NOx, large uncertainties exist in regional emission inventories due to limited observational constraints. Stable isotopic signature of particulate NO3- serves as an excellent tool to understand its formation pathways and sources of its precursor. Here, we have applied a dual-isotope (δ15N and δ18O) approach to understand seasonal and diurnal variations in NO3- formation pathways and NOx sources over Ahmedabad, an urban megacity in western India, during winter and summer. In winter, overall particulate NO3- formation was driven mainly by the OH oxidation pathway (P1, 61.9 ± 7%) and N2O5 hydrolysis (P2, 24.6 ± 6%), with smaller contributions from VOC-derived (P3, 7.6 ± 4%) and ClNO2 pathways (P4, 5.9 ± 3%). However, strong diurnal contrasts were evident, with P1 accounting for 69.4 ± 5% during the day and P2 increasing to 32.8 ± 7% at night, reflecting enhanced photochemical activity during day and nocturnal buildup of N2O5 under cooler, low-light conditions at night. In summer, NO3- formation was dominated by the OH pathway throughout the day and night (67.5 ± 7%), with no significant diurnal variability. This seasonal shift was attributed to elevated boundary layer height and enhanced atmospheric mixing, which stabilized particulate NO3-, which was particularly associated with stable non-volatile cations. Source apportionment of NOx using the Bayesian model (MixSIAR) revealed no significant diurnal differences within either season; however, a distinct seasonal pattern in NOx sources was observed. In winter, traffic was the largest contributor (46.7 ± 19%), followed by soil emissions (24.4 ± 12%), biomass burning (18.0 ± 9%), and coal-fired power plants (10.9 ± 8%). In summer, soil-related emissions increased to 38.4 ± 12% due to temperature-enhanced microbial activity and volatilization from urban waste, livestock areas, and fertilized land, while traffic remained a dominant source (40.1 ± 17%). Biomass burning and power plant contributions remained lower but persistent across both seasons. Together, these results provided the first dual-isotope-based evidence from western India showing how meteorology and emission processes jointly influence NO3- formation and NOx source, thus offering critical observational insight needed to improve regional nitrogen budgets and air quality mitigation strategies.
How to cite: Shaw, C., Rastogi, N., Mandal, R., and Sanyal, P.: Sources and formation pathways of particulate nitrate over the western India: Insights through δ15N and δ18O isotopes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-128, https://doi.org/10.5194/egusphere-egu26-128, 2026.
Excessive reactive nitrogen (Nr) is a growing challenge for sensitive terrestrial habitats like forests. Nepal is experiencing threats of nitrogen (N) pollution largely transported from the Indo-Gangetic Plain (IGP) – a global nitrogen pollution hotspot – which affects biodiversity, ecosystem functioning and human health. This urges the quantification of the impacts of those pollutants in the Himalayan region. Our analysis, based on the atmospheric chemistry transport model (European Monitoring and Evaluation Programme-Weather Research and Forecasting 2010 emission with 2018 chemistry and meteorology) with land use land cover and digital elevation model, shows that 95-99% of Nepal’s forests have already exceeded the United Nations Economic Commission for Europe (UNECE)-recommended ammonia (NH3) critical levels and N critical loads. Overall, ammonia (NH3) (0.54-13.13 μg m–3) and nitrogen oxides (NOx; 0.05-13.64 μg m–3) concentrations are higher at low elevation forests, but a contrasting pattern of bulk N deposition (4.52-38.56 kg N ha–1 yr–1) is observed in forests along the elevation gradients and forest types. Wet deposition of N is exceptionally high in forested areas receiving high precipitation, but dry deposition is heterogeneously distributed over different parts of the country. The forests in the lowland Tarai and Mid-hills that are near IGP are exposed to high concentrations of NH3 and NOx – thus are at a higher risk of biodiversity loss. Contributing only small shares, deciduous and needleleaf forests are vulnerable to N pollution as they cover the subtropical to subalpine region of the Mid-hills and host most of the sensitive species like lichens. This demonstrates a serious concern of N pollution on biodiversity and ecosystem services in the region. The empirical testing of N impacts on Nepal’s forested ecosystems is now crucial to establish the field-based toxicity threshold of N-based pollutants for biodiversity conservation and policy negotiation.
How to cite: Pradhan, S. P., Ellis, C. J., Deshpande, A. G., Wang, Y., Vieno, M., Jones, M. R., Rai, S. K., Raut, N., Weerakoon, G., Stevenson, D. S., and Sutton, M. A.: Nitrogen air pollution concerns for Nepal’s forested ecosystems and lichen bioindicators , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-914, https://doi.org/10.5194/egusphere-egu26-914, 2026.
The transition towards circular nutrient management requires fertilizers that enhance nitrogen (N) use efficiency while minimizing environmental losses. Struvite, a recovered magnesium ammonium phosphate, is increasingly proposed as an alternative to conventional mineral fertilizers such as monoammonium phosphate (MAP). However, the extent to which fertilizer chemistry interacts with soil properties to regulate microbial functioning and N cycling processes remains insufficiently understood.
In this study, we investigated short-term N transformations, microbial activity, and greenhouse gas emissions in two agricultural soils differing in pH (acidic and alkaline) following fertilization with struvite and MAP. Soils were incubated under controlled conditions, and temporal changes in mineral N forms, soil chemical properties, and CO₂ and N₂O emissions were monitored. Microbial respiration and growth were quantified to assess microbial carbon use efficiency (CUE) and biomass turnover. To resolve underlying process rates beyond net fluxes, stable isotope techniques were applied to quantify gross ammonium and nitrate production and consumption, allowing the calculation of microbial nitrogen use efficiency (M-NUE).
Fertilizer effects were strongly regulated by soil pH. In acidic soil, struvite promoted a more gradual and microbially efficient N turnover compared to MAP, characterized by distinct ammonium and nitrate transformation pathways and higher M-NUE. In alkaline soil, N cycling was dominated by rapid nitrification, which reduced functional differences between fertilizer types. Across both soils, fertilizer-specific shifts in microbial growth, CUE, and biomass turnover revealed changes in microbial resource allocation and N processing pathways.
By integrating gas flux measurements, microbial efficiency indicators, and stable isotope–derived gross N transformation rates, this study highlights how soil chemical context governs the biogeochemical performance of recovered fertilizers. Our findings emphasize the need to account for soil pH and microbial functioning when optimizing the use of struvite and other circular fertilizers in sustainable agricultural systems.
How to cite: Alberghini, M., Friedl, J., Rosinger, C., Weinrich, F., Hood-Nowotny, R., Ferretti, G., Keiblinger, K., and Coltorti, M.: From fertilizer form to microbial function: soil pH controls nitrogen cycling pathways under conventional and recovered phosphorus fertilization, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5550, https://doi.org/10.5194/egusphere-egu26-5550, 2026.
Degrading topsoil, declining habitat and biodiversity, climate change and social and political unrest alongside a growing population and demand for food are calling for a sustainable alternative to the current industrialised agricultural systems. Permaculture and agroecology are two potential alternative sustainable food systems that are currently lacking scientific evidence base. This study compared the two alternative management approaches against a conventionally practiced control in terms of their soil fertility, microbial abundance and diversity (via PLFA analysis) and greenhouse gas mitigation potential. The permaculture site comprised of a no-dig, organically amended market garden for vegetable production, while the agroecology site was minimally tilled and organically amended, whereas the control was tilled & fertilised with a legacy of herbicide and pesticide use. Monthly soil sampling and greenhouse gas emission monitoring via closed chambers over a 12-month period assessed the soils biogeochemistry, microbial abundance and greenhouse gas fluxes. Permaculture soils supported the most abundant microbial community, with an annual mean total microbial biomass of 89.92 ± 20.84 µg g-1 (23.23 ± 30.7 µg g-1 and 28.69 ± 30.7 µg g-1, more than the minimally tilled and conventionally managed soil, respectively). The same soils also exhibited more than double soil organic matter content (annual mean 16.87%) relative to the conventional management, alongside a significantly lower proportion of soil organic carbon (SOC) loss as CO2 (1.98%, compared to 7% under conventional management). Surprisingly, nitrous oxide (N2O) fluxes at the conventional site were limited, despite the build-up of the soil nitrate pool during summer, which was attributed to the exceptionally dry soil conditions that prevailed during the year of study, suppressing microbial N2O production. However, the denitrification product ratio (N2O/N2+N2O) was consistently lower under permaculture soils compared with agroecology and conventional soils, an indication of a strong potential for N2O emission mitigation. Seasonal warming during spring further stimulated microbial activity, accelerating nutrient acquisition and carbon turnover, with permaculture no-dig soils maintaining three times greater total soil carbon (0.67 ± 0.02 %, annual mean), suggesting a more stable carbon pool. Overall, this study demonstrates permaculture and agroecology practices, particularly no dig management combined with organic amendments, enhances soil fertility, microbial activity, and carbon retention, indicative of a more balanced food system. Multi-year assessments across contrasting climatic conditions are warranted to reduce the uncertainty of temporal variability in GHG flux dynamics and assess long-term carbon stability under these managements.
How to cite: Sgouridis, F., Williamson, R., Reay, M., and Williamson, C.: The effect of sustainable agricultural land managements (agroecology & permaculture) on soil nitrogen and carbon cycling, microbial diversity and greenhouse gas emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5670, https://doi.org/10.5194/egusphere-egu26-5670, 2026.
Soil nitrogen (N) supply and plant N acquisition strategies are central to species coexistence and ecosystem functioning, but how topography regulates plant N acquisition strategies remains poorly understood. Here, we used 15N natural abundance approach to quantify plant N uptake proportions along a valley to slope gradient in Southwest China. We further measured leaf and root functional traits with soil N transformation rates to explore topography controls of plant N acquisition strategies.
The results showed that soil nitrate (NO3–), decreased significantly from valley to slope, whereas soil ammonium (NH4+) and extractable organic N (EON) increased significantly. These differences were attributed to distinct soil N transformation pathways, with markedly higher soil N mineralization and nitrification rates in valley soils. Consistent with the shifts of soil N availability, plants predominantly utilized NO3– (83.1%) in the valley, but markedly increased the uptake proportions of organic N and NH4+ at slope. In addition, leaf functional traits shifted from an acquisitive strategy in valley plants, characterized by high leaf N concentrations, to a conservative strategy in slope plants with higher leaf carbon (C) to N ratios and increased leaf thickness. In contrast, root functional traits changed from “amount” strategies in the valley, indicated by high specific root length, to “efficiency” strategies reflected by high root N uptake rates at slope. Our structural modeling indicated that topography-driven shifts in plant biomass, leaf and root C: N, soil physicochemical properties, and soil enzyme activity constrain soil N mineralization and nitrification rates on slopes, thereby increasing the relative contribution of EON and NH4+ in soils and driving a corresponding shift in plant N acquisition strategies.
Together, these findings highlight that plants adapt to topography-driven variations in soil N supply by coordinating above and belowground functional traits. Our results provide a scientific basis for future forest restoration and species selection across topographic gradients.
How to cite: Yang, S. and Zhu, T.: Topography-driven divergence of plant nitrogen acquisition strategies in forests, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5881, https://doi.org/10.5194/egusphere-egu26-5881, 2026.
Quantifying the response of cropland N2O emissions to future warming is critical for predicting the feedback between nitrogen cycling and climate change. A central uncertainty is whether soil N2O emissions thermally adapts, an assumption often invoked in carbon-cycle theory. If present, both the magnitude and mechanistic basis of this adaptation remain unresolved. Here, using a global compilation of N₂O flux measurements from temperature-controlled incubations of cropland soils, we identify mean annual temperature (MAT) as the dominant predictor of N2O fluxes and their temperature sensitivity (Q₁₀). Along the MAT gradient, N2O fluxes at a reference temperature (25 ℃) declined by 12.2 ± 2.6% (mean ± SE) per °C, and Q₁₀ decreased by 0.05 ± 0.01 per °C. To probe mechanisms, we conducted two complementary experiments using soil samples spanning climate gradients: a short-term temperature-response assay and a 90-day warming incubation, both under controlled moisture and with 15N-labelled substrate additions. Across both datasets, warmer thermal regimes (higher MAT and experimental warming) reconfigured temperature response curves toward lower Q10 and higher Topt (temperature optima) for both nitrification and denitrification. Mechanistically, this pattern is aligning with the compensatory theory, microbial N2O production rates normalized to mean nitrifier and denitrifier RNA abundances were reduced under warmer thermal regimes. Together, these findings highlighted that soil N₂O production adapts to local thermal regimes across space and to sustained warming through time, implying that future warming may amplify cropland N₂O emissions, but less than commonly predicted.
How to cite: Zhang, W., Nie, M., and Zhou, F.: Quantifying thermal adaptation of cropland N2O emissions and its compensatory microbial basis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6968, https://doi.org/10.5194/egusphere-egu26-6968, 2026.
Nitrous acid (HONO) is a key precursor to hydroxyl radicals (OH) and a reservoir of reactive nitrogen, yet the processes sustaining elevated daytime HONO in marine and coastal environments remain poorly understood. We combine coastal field observations with irradiation chamber experiments and atmospheric modeling to identify abiotic photodecomposition of marine algae as a previously unrecognized HONO source. During Ulva prolifera green tides, daytime HONO levels in the coastal atmosphere closely followed tidal cycles and peaked at low tide, in contrast to typical inland nocturnal peaks. Chamber experiments confirm that common algae (Ulva prolifera, Bryopsis plumosa, Chaetomorpha spiralis Okam., Sargassum, and Silvetia siliquosa) directly emit HONO under irradiation, with fluxes increasing with light intensity and algal surface area. Measured HONO fluxes of 1.08 × 10–7 to 2.31 × 10–6 mol m–2 h–1are comparable to reported soil HONO emissions and exceed marine NO fluxes by 2 to 3 orders of magnitude. Incorporating this source into an atmospheric model increases HONO concentrations, enhancing OH and ozone production and accelerating the oxidative loss of dimethyl sulfide and methane. As eutrophication and warming intensify algal blooms worldwide, algal photodecomposition is likely to become an increasingly important driver of coastal reactive nitrogen emissions and oxidation capacity.
How to cite: zhong, X., shen, H., and xue, L.: HONO Emission from Marine Algae, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8551, https://doi.org/10.5194/egusphere-egu26-8551, 2026.
Soil nitrogen (N) availability and plant N uptake strategies are central to species adaptation and community assembly, yet how lithology shapes soil N supply and plant N uptake remains poorly understood. Here, we used 15N labeling to compare soil N supply and plant N uptake preferences in forests on soils developed from limestone and clastic rocks, respectively. Our results revealed significant contrasts in inorganic N pools: nitrate (NO3–) dominated in limestone soils, while ammonium (NH4+) was more abundant in red soils developed from clastic rocks. We attributed these differences to different soil N transformation pathways. Increased nitrification rates in limestone soils increased NO3– content, whereas red soils exhibited high mineralization but lower nitrification rates, leading to NH4+ dominating inorganic N. Forest plants in both limestone and red soils preferentially utilized NH4+ as their primary N source. However, plant in limestone soils took up significantly higher proportions of NO3– and glycine. Moreover, total N uptake rates by plants were significantly larger in limestone than red soils, suggesting a more efficient N acquisition strategy. Structural equation modeling indicated that lithology significantly affected soil N mineralization and nitrification by regulating soil pH and total N, thereby driving differences in soil inorganic N pools and ultimately plant N uptake. Our results provide evidence that lithology-driven variations in soil N supply can strongly affect plant N acquisition strategies.
How to cite: Dörsch, P., Yang, S., and Zhu, T.: Lithology controls of soil N availability and plant N acquisition strategies in subtropic forests, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13347, https://doi.org/10.5194/egusphere-egu26-13347, 2026.
Nordic agricultural production faces multiple challenges in a warming climate. Although predictions indicate an overall increase in annual mean precipitation in northern Europe, increasing temperatures may lead to earlier snowmelt and drying of soil during springtime, as well as longer growing season and higher evapotranspiration increasing the risk of summer droughts. The use of cover crops in agriculture is one of the climate-smart practices that have multiple benefits, such as increasing SOC, reducing N losses, and increasing biodiversity. Still, the question whether cover crops and their diversity increase resilience against climate extremes such as drought, and how the combined effects of cover crops, their diversity and drought affect greenhouse gas (GHG) emissions from soil remain largely unknown. We studied the effect of cover crop diversity and drought on soil and crop C and N dynamics and GHG (CO2, N2O) emissions in a biodiversity cropland experiment with or without shelters that remove 50% of incoming precipitation for two years. GHG emissions were measured with the manual dark chamber method twice a week during growing season and once a week during off-season. Soil temperature and water content were measured continuously, and the soil was sampled for mineral N and total C and N analysis seasonally.
The preliminary results showed that reduced rainfall did not affect N2O emissions significantly during the growing season in either year. During off-season, reduced rainfall led to elevated N2O emissions irrespective of cover crop diversity treatments. However, the effect was absent in the second year, indicating that factors other than drought were driving the N2O production. Contrary to N2O, drought did not affect CO2 emissions during off-season in either year. Overall, during both years off-season N2O emissions dominated the annual N2O balance in all diversity treatments, highlighting the importance of including off-season measurements to the annual N2O balance estimation.
How to cite: Turunen, P., Simojoki, A., Koskinen, M., Heinonsalo, J., and Pihlatie, M.: Seasonal patterns of N2O and CO2 emissions from Finnish agricultural soil under oat with and without cover crops as affected by reduced rainfall, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16945, https://doi.org/10.5194/egusphere-egu26-16945, 2026.
As peat extraction for energy has declined in Europe, extensive areas released from peat production require sustainable after-use. This land use change provides opportunities to mitigate climate change, halt biodiversity loss and support socially fair and rewarding solutions for communities. Here we present the first results from PaluWise project’s large 50 ha peat extraction area converted into demonstration site of paludiculture i.e., the productive land use of rewetted peatlands that preserves the peat soil and thereby reduces carbon dioxide (CO2) and nitrous oxide (N2O) emissions and subsidence. The risks related to paludiculture include increased methane (CH4) emissions, high nutrient losses and wetting the surrounding fields. We also reviewed evidence from climate change mitigation potential of common after-use options in agriculture and forestry for peat extraction areas in Northern Europe (ALFAwetlands project). Our data synthesis of annual greenhouse gas (GHG) fluxes revealed that boreal paludiculture showed a net loss of carbon (C) based on the net ecosystem C balance at least in the short term after rewetting cultivated peat soil. A woody crop, short rotation coppice of willow had more favourable greenhouse gas balance than forage and set-aside treatments during 4 years after transition. Options enhancing C input to the soil without rewetting may stop net annual C losses from a former peat extraction site just in one year: Afforestation on Scots pine with fertilization turned the site fast into a CO2 sink, as measured by eddy covariance technique. We hypothesize that woody crops having low nutrient requirements and potential for added value products may offer a win-win after-use solution for rewetted peat extraction areas. We examined biomass and CO2, CH4 and N2O fluxes from stands of downy birch and colonizing wild vegetation at our demonstration site. We found that the first Sphagnum mosses co-occur with downy birch, indicating favourable conditions for enhanced C sequestration. We expect that land use decisions may optimize many targets: climate, biodiversity, water quality, and economy simultaneously. Confounding factors, e.g. time perspective may affect landowner’s preferences. Long-term changes in peat carbon stock under any after-use option require further study.
How to cite: Larmola, T., Sarkkola, S., Juutinen, S., Rautakoski, H., Linkosalmi, M., Jauhiainen, J., Aurela, M., Ukonmaanaho, L., and Merilä, P.: Woody paludiculture as an after-use option for peat extraction fields , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17046, https://doi.org/10.5194/egusphere-egu26-17046, 2026.
Arctic permafrost-affected soils serve as one of Earth’s most significant terrestrial reservoirs of nitrogen (N), storing an estimated 55 Pg of total N within the first three meters of the soil. Ongoing anthropogenic climate change is causing permafrost soils to thaw at greater depths each summer, rendering part of vast pools of N stored in the permafrost accessible to plant uptake and microbial processing. However, little is known of the magnitudes and consequences of the potential increase of N availability due to permafrost thaw, as the mobilisation and mineralisation of this N has the potential to alter ecosystem productivity, as well as increase emissions of reactive nitrogen gases, such as nitrous oxide (N2O). This research aims to quantify nitrogen dynamics across the Arctic following permafrost thaw from the historical period to the end of the twenty-first century.
In our study, we first estimate the total amount of soil N that will be mobilized through thawing. To do this, we combine a vertically-resolved high spatial resolution soil C and N dataset with future projections of pan-Arctic active layer depth changes derived from five CMIP6 models across four climate change scenarios. Vertical mean soil N profiles were thereby determined for different land cover types of the tundra, taiga, wetlands and barren biomes. Secondly, we estimated the amount of permafrost organic soil N that is rapidly mineralized to bioavailable forms, was determined from a temperature-dependent mineralisation flux estimation. Finally, we perform a first-order estimation of the impact of the additional bioavailable N for Arctic vegetation NPP and N2O emissions.
Across the CMIP6 models, the pan-Arctic mean maximum active layer depth is projected to increase by an additional 1 - 2.65 m by 2100 (SSP 1-2.6 to 5-8.5), relative to present-day conditions. This increase corresponds to a potential cumulative release of 20 - 44 Pg total N by the end of the century, of which 4.4 - 5.5 % may be mineralised rapidly under projected soil warming. Putting these estimates into context with our novel budget of present-day pan-Arctic N fluxes, we show that the addition of reactive nitrogen from the permafrost will consist of an important part of N sources to the Arctic in the future (40-50 %).
Based on our synthesis of N fertilisation effects on Arctic vegetation net primary productivity (boreal ANPP: 14.1 (+/- 3.55) g C / g N, BNPP: 2.82 g C / g N; tundra ANPP: 2.66 (+/- 2.22) C / N, BNPP: 2.29 (+/- 4.41) g C / g N), we furthermore quantify that the release of N from the permafrost could increase NPP by 150 – 400 Tg C yr-1 until year 2100. In a similar approach based on soil manipulation experiments, we also estimate a potential additional 0.12 – 0.8 Tg N yr-1 in N2O emissions by the year 2100.
Our results show that permafrost thawing will significantly alter the Arctic N budget, having very likely substantial impacts for both terrestrial NPP and as N2O emissions.
How to cite: Oxley, L. R., Stocker, B. D., Zähle, S., Zhu, Y., and Lacroix, F.: Petagrams of Nitrogen released from the Permafrost affect Arctic Ecosystem Fluxes under any Climate Scenario, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17105, https://doi.org/10.5194/egusphere-egu26-17105, 2026.
The Arctic is warming four times faster than the global average, triggering the widespread degradation of permafrost and enhancing mobilization of vast, previously frozen soil nitrogen (N) and carbon (C) stocks. While C release associated with permafrost thaw is better documented, the liberation of permafrost N, a potential precursor to the strong greenhouse gas (GHG) nitrous oxide (N2O), remains a critical knowledge gap. This is particularly relevant for ice-rich Yedoma deposits, which are highly vulnerable to abrupt thaw and the formation of disturbance features, such as retrogressive thaw slumps (RTSs), thermokarst lakes, and drained thermokarst lake basins (DTLBs). While RTSs are known hotspots for N2O, recently formed DTLBs underlain by ice-rich Yedoma deposits with a high content of buried, poorly decomposed organic matter, remain largely understudied, although they are widespread across Yedoma landscapes. Importantly, there are no studies reporting N2O fluxes from DTLBs, despite the high N mineralization expected after drainage, which might support high emissions.
Here, we report N2O fluxes and N turnover processes from RTS and DLB on the Baldwin Peninsula, Western Alaska, underlain by ice-rich late Pleistocene Yedoma deposits. In situ fluxes were measured during the summer of 2024, alongside aerial surveys for high-resolution elevation and vegetation mapping with lidar and optical cameras. We conducted laboratory incubations for GHG production, including denitrification and 15N labeling to quantify gross rates of mineralization, nitrification, and dissimilatory nitrate reduction to ammonium (DNRA) using the 15N tracer method.
Our study reveals high N2O emissions at both disturbance sites, demonstrating that DTLBs are emerging as significant sources of N2O (up to 7.7 mg N m-2 d-1) emissions, comparable to known high emissions from thaw slumps. supported by high nitrate concentrations, reaching up to 205.1 µg N gDW-1. We identified the role of environmental factors in driving the spatial variability in N2O fluxes as well as N cycling. These findings suggest that as thermokarst lake drainage events increase across the Arctic, DTLBs in Yedoma uplands represent a major, expanding source of permafrost-driven N emissions that must be integrated into global climate feedback models. By tracking how N moves through the soil and how different environmental conditions, like moisture and thaw, trigger specific microbial processes, we can better understand the overall behavior of the N cycle and its growing role in these disturbance landforms.
How to cite: Hashmi, W., Martinez-Risco Martinez, P., Sanders, T., Veremeeva, A., Nitze, I., Gil, J., Rütting, T., Paul, D., Strauss, J., C. Treat, C., and E. Marushchak, M.: When Yedoma permafrost thaws: disturbances from lake drainage to thaw slump, and their impact on nitrogen cycling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17133, https://doi.org/10.5194/egusphere-egu26-17133, 2026.
The input of reactive nitrogen sourced from anthropogenic activities such as smallholder farming as well as changes in its transport and fate in the environment may alter the nitrogen balance of a catchment and the nitrogen use efficiency for crop production. Both have the potential of causing detrimental effects on agricultural productivity and the environment such as water bodies. Insufficient nitrogen addition for crop production could lead to soil nitrogen depletion, while too high input rates could lead to excess nitrogen polluting water bodies. In the Mau Forest Complex (MFC) in Kenya, fertilizers and livestock management have been assumed to be associated with the increase in annual riverine export of reactive nitrogen. Twice the annual export of nitrogen from a catchment dominated by smallholder agriculture was reported compared to that from the native forest. To assess the role of smallholder agriculture in nitrogen losses, this study aims at determining the nitrogen balance and nitrogen use efficiency of a 27 km² headwater catchment characterized by smallholder farming in the MFC. Anthropogenic inputs and outputs were estimated from a household survey (n=185), field measurements involving precipitation collectors in 10 different locations as well as literature review. The nitrogen flows in the native forest were obtained from the literature.
Results show that at farm scale, about one third of investigated farms have negative nitrogen balances, while at the catchment scale the aggregate nitrogen balance is −10.9 kg N ha−1 yr−1. This is in contrast to the positive nitrogen balance of the native forest of 26.5 kg N ha−1 yr−1. With respect to the nitrogen use efficiency only 20% and 18% of the maize fields as well as 7% and 12% of the potato fields, recorded nutrient use efficiency between 50% and 90% in 2018 and 2019, respectively.
The study shows that inorganic fertilisers, atmospheric deposition and biological fixation are the most important sources of reactive nitrogen, while crop harvest, denitrification and leaching were identified as major loss pathways. The wide range of nitrogen surplus and deficits among farms and the subsequent potential for eutrophication and soil mining highlight the need to better educate farmers on the optimal use and timing of fertiliser application to close the deficit gap and prevent pollution.
How to cite: Kasebele, M., Jacobs, S., and Breuer, L.: Nitrogen balance and nitrogen use efficiency in an East African tropical montane catchment characterised by smallholder farming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17418, https://doi.org/10.5194/egusphere-egu26-17418, 2026.
Tropical wetlands are among the most important regulators of the global carbon (C) and nitrogen (N) cycles, largely through microbially mediated processes that control greenhouse gas (GHG) production and consumption. Tropical peat forests play a key role in these biogeochemical cycles by storing large amounts of organic matter and regulating gas exchanges between soils and the atmosphere, with their functioning strongly influenced by vegetation composition and seasonal shifts between dry and rainy periods. Amazonian peatlands are emerging as potentially significant sources and sinks of nitrous oxide (N2O) and methane (CH4), depending on climatic conditions and climate change, including more frequent droughts and increasing irregularity between rainy and dry seasons. Despite their importance for climate regulation, the links between peat forest structure, microbial C and N cycling, and ecosystem-scale GHG fluxes remain poorly quantified. In addition to vascular plants, cryptogams such as mosses and lichens may exert important yet understudied controls on microbial activity, thereby potentially affecting N2O and CH4 emissions in aboveground compartments.
This study aims to assess how cryptogam-associated microbial processes affect N2O and CH4 fluxes in the Quistococha peat swamp forest and Zungarococha secondary peat swamp forest of Peruvian Amazon, and to evaluate how these processes differ between forest types.
A total of 25 cryptogam samples were collected from two sites in the Loreto Region of northern Peru. Quistococha is an intact peat swamp forest dominated by Mauritia, Tabebuya, and Caspi, whereas Zungarococha is a secondary peat swamp forest dominated by Cashapona, Mauritia, Hebea, Caspi, M_Beuna, Symphonia, and Cumala. Samples were collected from the stems of trees and palms during two campaigns, in rainy and dry seasons. Metagenomic sequencing of cryptogams was performed to investigate microbial functional potential related to C and N cycling and its relationship with forest type.
Our results show that: (1) Cashapona, Caspi, Cumala, and Hebea exhibited similar functional gene abundance patterns across different seasons and sites, suggesting relatively stable microbial functional characteristics; (2) genes associated with N fixation, dissimilatory nitrate reduction to ammonium (DNRA), and nitrification–processes regulating N availability and potential N2O production–were more abundant in Zungarococha, especially during the rainy season; (3) genes related to methanogenesis (CH4 production) and methanotrophy (CH4 oxidation) were present at relatively low abundances at both sites, with no significant seasonal differences; (4) most functional genes related to C and N cycling were more abundant in Zungarococha than in Quistococha, with peak abundances during the rainy season , whereas in Quistococha, genes related to methanotrophy, N fixation, nitrification, and denitrification (also influencing N2O consumption) were more abundant during the dry season; (5) Burkholderiaceae and Methanobacteria were more abundant in Zungarococha, Methylococcales and Opitutae were more abundant during the dry season, and Oscillatoriales were more abundant in the rainy season, which are affecting C and N cycling.
How to cite: Chen, S., Mander, Ü., Khanongnuch, R., Kazmi, F. A., Masta, M., Soosaar, K., Fachin-Malaverri, L., and Espenberg, M.: Cryptogam-associated microbial processes shaping N2O and CH4 cycling in Amazonian peat swamp forests, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17679, https://doi.org/10.5194/egusphere-egu26-17679, 2026.
Iron exists abundantly in soil in multiple oxidation states and mineral forms, and is the dominant redox-active metal. Recent evidence suggests iron chemistry plays a central role in producing volatile reactive nitrogen oxides (NOy = NO + NO2 + HONO + other N-oxides), which are key air pollutants contributing to tropospheric ozone formation, acid deposition, and respiratory health risks. Current atmospheric models do not accurately represent soil NOy fluxes, particularly HONO and NO₂, because biogenic production mechanisms remain poorly characterised. In moist soils, HONO is primarily produced by bacterial and archaeal ammonia oxidisers. However, as soils dry, nitrite and nitrate can accumulate and pH often decreases, potentially favouring abiotic nitrate reduction as a critical HONO source.
To investigate how soil iron mineralogy, concentration, and speciation influence NOy emissions during drying, HONO and NO₂ fluxes are measured over 24 hours using an ICAD-HONO/NO₂-210L system (Airyx GmbH) from soil microcosms amended with three iron oxides (ferrihydrite, goethite, magnetite) at two concentrations (3.5% and 4.5% total iron). Microbial community responses will also be assessed via quantitative PCR targeting nitrogen cycling genes. We hypothesise that: 1) soil drying will increase nitrate accumulation and lower pH, leading to HONO fluxes that peak at intermediate moisture when thin water films enable reactions but allow gas diffusion; 2) ferrihydrite-amended soils will exhibit the highest NOy emissions due to its Fe³⁺ reduction potential, transition metal adsorption, and reactive oxygen species generation; and 3) NOy emissions will increase with iron oxide concentration, although high concentrations may suppress microbial activity via metal toxicity.
Preliminary results show substantial HONO emissions from all iron amendments in neutral soils (~pH 7), followed by a steep decline as soils dry. A late NO₂ peak was observed, possibly due to physical release during drying or shifts in microbial pathways. Increasing goethite concentrations correlated with higher HONO emissions, whereas ferrihydrite showed a negative correlation. Future work will examine the pH modulation of the relationship between iron and NOy fluxes by repeating flux measurements in acidic soils (~pH 5.5), where we expect enhanced nitrite protonation, and altered iron solubility and redox activity.
How to cite: Purchase, M. L., Waez, C., Thorpe, A. J., and Mushinski, R. M.: Influence of Iron Mineralogy on Reactive Nitrogen Gas Emissions from Soil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18666, https://doi.org/10.5194/egusphere-egu26-18666, 2026.
Salinization is an increasing threat to global food security. Sea-level rise and storm surges drive coastal salinization, while inland salinization is driven by intensive fertilization and low-quality irrigation. High salt levels cause osmotic stress, which impairs plant growth and microbial activity, ultimately degrading soil health and food production. Both the EU and UN recognize soil salinization as a major global challenge requiring urgent action.
This study is part of the EJP SOIL project SoilSalAdapt, with Norwegian partners funded by the Research Council of Norway. The project explores adaptation strategies to soil salinization in a temperate climate. Experiments indicate that controlled saline irrigation can promote salt tolerance in soil microbes, suggesting that saline irrigation may serve as a proactive climate adaptation measure. This sub-study examines the legacy effect of previous salt exposure on soil biogeochemical turnover of carbon and nitrogen in response to a new shock salinization event.
Specifically, this study investigates 1) oxic microbial respiration and carbon use efficiency, 2) anoxic respiration and denitrification end-product stoichiometry, and 3) nitrification potential rates and the relative contributions of ammonia-oxidizing bacteria and archaea.
Denitrification completeness was strongly impacted by the salt treatment, particularly in the low-fertilization scenario, were salt seems to reduce nitrous oxide production per total denitrification. Nitrification rates responded differently to historical salinity in clay and sand soils, but the saline shock converged rates across soil types at a lower overall level.
At the EGU conference, I will present our findings and discuss how soil-based adaptation strategies can support resilient food production under ongoing and future climate pressures.
How to cite: Kyllingstad, R., Dörsch, P., and Almås, Å.: Adapting soils to salt: Effects of saline irrigation on soil C and N turnover, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19174, https://doi.org/10.5194/egusphere-egu26-19174, 2026.
Nutrient loss from land use is a major cause of water-quality problems worldwide. High inputs of nitrogen (N) and phosphorus (P) to rivers, lakes, and coastal waters drive eutrophication, reduce aquatic biodiversity, and damage ecosystem services. In many regions, policy frameworks such as the European Union Water Framework Directive require reliable estimates of nutrient pressures to support effective water-quality management. However, measured load data are often limited or inconsistent, particularly at large spatial scales. As a result, export-coefficient (EC) approaches are widely used to estimate nutrient losses from land use. A continuing challenge is ensuring that the coefficients applied are relevant to the environmental context and selected in a consistent and transparent way, especially when values are transferred from international studies.
This study develops a harmonised framework for selecting and applying nutrient export coefficients based on international literature. A structured decision-tree approach is used to systematically assess whether published export coefficients are suitable for application under different climatic and environmental conditions. Each coefficient is screened against six practical criteria: compatibility with local land-use systems, similarity of soil types, relevance of climatic setting, comparability of dominant hydrological pathways, suitability of reporting format for load calculation, and study reliability—evaluated based on the quality of methods, length of monitoring, and peer-review status.
The framework is demonstrated using Ireland as a case study, and the analysis also compares how different land-cover datasets influence national nutrient export estimates. Three datasets are used to explore the effect of spatial representation: the Irish National Land Cover Map 2018 and the CORINE 2012 and 2018 Land Cover maps. National nutrient exports are calculated by multiplying harmonised export coefficients by mapped land-use areas and compared with a national benchmark study, the Source Load Apportionment Model (SLAM).
Across the different land-cover datasets, nutrient export coefficients derived from the framework show strong agreement with SLAM in estimating national nitrogen loads. This suggests that the decision-tree framework supports the selection of export coefficients for dominant agricultural systems, which are the main drivers of nitrogen loss. In contrast, larger differences between SLAM and framework-based estimates are observed for phosphorus, particularly in peatlands, wetlands, and forestry areas. This reflects both the higher sensitivity of phosphorus to coefficient choice and the influence of land-cover representation. Differences between land-cover datasets lead to significant changes in the mapped extent of organic soils and semi-natural land uses, resulting in notable variation in national phosphorus estimates. These findings show that even when identical export coefficients are applied, national nutrient totals can vary substantially depending on the structure and resolution of the underlying spatial data.
Overall, this study demonstrates that combining harmonised export coefficients with high-resolution land-cover data provides a robust and adaptable basis for national-scale nutrient modelling. The close agreement with SLAM for nitrogen supports the validity of the approach for dominant agricultural pressures, while the divergence observed for phosphorus highlights the need for improved representation of peatlands, wetlands, and forestry in national frameworks.
How to cite: Alighanbari, S.: Developing a harmonised framework to model nutrient emissions from land uses: a case study from Ireland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20909, https://doi.org/10.5194/egusphere-egu26-20909, 2026.
Nitrogen is a fundamental plant nutrient and important fertilizer in modern agriculture, while nitrate-based nitrogen losses from agroecosystems become an increasing problem in ground- and surface waters. To reduce the emission of nitrate from agricultural soil, substantial efforts were made in regulation and assessment of plant specific fertilizer needs to reduce fertilization excess. Unfortunately, those efforts have not yet led to a considerable reduction of nitrate loadings in ground and seepage water under agricultural land use. This lag of response is often explained with residence and transport times in groundwater and a potential contribution of nitrogen legacies accumulated in soils.
Since 1980 the water and solute balances of different soils under agricultural land use are investigated at the lysimeter station Brandis (Saxony, Germany). Additionally, historic marking experiments with 15N enriched fertilizers were performed on some of the investigated soils. The combination of the long-term nitrogen balances together with an 15N isotope measurement campaign clearly show, that in a broad range of soils:
- a substantial amount of the historic fertilizer excess has accumulated in the soils
- historic fertilizations with 15N enriched fertilizer are still visible in the top soils after 40 years of agricultural landuse
- nitrogen residence times are independent of water transport times
- nitrate loss from soil organic matter pools is a major source of nitrate lost by seepage water
Our results clearly show, that substantial nitrogen legacies from fertilization excess can accumulate in a broad range of soil types. It becomes evident that considering and understanding the dynamics of this biochemical nitrogen legacy in agricultural soils is key to explain the lag of response in water quality observations in ground- and surface waters.
How to cite: Werisch, S. and Alexandra, T.: Nitrogen legacies in agricultural soils? Evidence from long-term lysimeter balances and isotope analyses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21159, https://doi.org/10.5194/egusphere-egu26-21159, 2026.
