BG1.6 | Nitrogen Cycling in the Anthropocene: Microbiological Processes, Land-atmosphere- Interactions and Global Change Feedbacks
EDI
Nitrogen Cycling in the Anthropocene: Microbiological Processes, Land-atmosphere- Interactions and Global Change Feedbacks
Co-organized by SSS5
Convener: Sami Ullah | Co-conveners: Li Li, Dianming Wu, Peter Dörsch, Tuula Larmola
Orals
| Tue, 16 Apr, 08:30–12:30 (CEST)
 
Room 2.23
Posters on site
| Attendance Tue, 16 Apr, 16:15–18:00 (CEST) | Display Tue, 16 Apr, 14:00–18:00
 
Hall X1
Orals |
Tue, 08:30
Tue, 16:15
Anthropogenic disturbance of the global nitrogen (N) cycle has more than doubled the amount of reactive N circulating in the terrestrial biosphere alone. Exchange of reactive/non-reactive nitrogen gases between land and atmosphere are strongly affecting Earth’s atmospheric composition, air quality, global warming, climate change and human health. This session seeks to improve our understanding of a) how intensification of reactive N use, land management and climate change affects the pools and fluxes of nitrogen in terrestrial and aquatic ecosystems, b) and how reactive N enrichment of land and water will affect the future carbon sink of natural ecosystems as well as atmospheric exchanges of reactive (NO, N2O, NH3, HONO, NO2 and non-reactive N (N2) gases with implications for global warming, climate change and air quality. We welcome contributions covering a wide range of experimental and modelling studies, which covers microbes-mediated and physico-chemical transformations and transport of nitrogen across the land-water-air continuum in natural ecosystems from local to regional and global scales. Furthermore, the interactions of nitrogen with other elemental cycles (e.g. phosphorus, carbon) and the impacts of these interactive feedbacks for soil health, biodiversity and water and air quality will be explored in this session. Latest developments in methodological innovations and observational and experimental approaches for unravelling the complexities of nitrogen transformations and transport will also be of interest.

Orals: Tue, 16 Apr | Room 2.23

Chairpersons: Sami Ullah, Li Li
Nitrogen cycling in forests, drylands, and beyond
08:30–08:35
08:35–08:55
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EGU24-17028
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solicited
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On-site presentation
Rossella Guerrieri, Joan Joan, Stefania Mattana, Emilio Casamayor, Josep Peñuelas, and Maurizio Mencuccini and the Collaborators at the ICP Forests sites

Fluxes and chemical composition of precipitation is substantially changed after passing through tree canopies, particularly in the case of atmospheric nitrogen compounds, with important implications on forest nitrogen cycling. The causes of these changes, however, have mostly focused on the passive role of foliar surfaces to scavenge pollutants from the atmosphere and to ion exchange processes, while biological processes involving microbes hidden in the phyllosphere have been less investigated. We combined triple oxygen isotopes approach and molecular analyses with the aim of quantifying canopy nitrification and identify microbes responsible for it, respectively. Ten sites included in the European ICP Forests monitoring network, chosen along climate and nitrogen deposition gradients, were selected to include the two most dominant tree species in Europe (Fagus sylvatica L. and Pinus sylvestris L.). Specifically, in this study we: 1) estimated the relative contribution of nitrate derived from biological canopy nitrification vs. atmospheric deposition by using δ18O and Δ17O of nitrate collected in water samples, i.e., in the open field (bulk deposition) and underneath tree canopies (throughfall); 2) quantified the functional genes related to nitrification for the two dominant tree species in European forests by using next-generation sequence analyses. Based on the isotope approach, we found that up to 80% of the nitrate reaching the soil via throughfall derived from biological transformations in the phyllosphere, equivalent to a flux of gross canopy nitrification of up to 5.76 kg N ha-1 y-1. The fraction of microbiologically derived nitrate increased with raising nitrogen deposition, thus suggesting that the process can be substrate limited. Molecular analyses confirmed the presence on foliar surfaces of bacterial and archaeal autotrophic ammonia oxidisers and bacterial autotrophic nitrite oxidisers across the investigate European forests. Our study demonstrates the potential of integrating stable isotopes with molecular analyses to advance our understanding on key processes underpinning forest nitrogen cycling, which should no longer exclude microbial processes occurring in the phyllosphere.

How to cite: Guerrieri, R., Joan, J., Mattana, S., Casamayor, E., Peñuelas, J., and Mencuccini, M. and the Collaborators at the ICP Forests sites: Quantifying tree canopy nitrification across European forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17028, https://doi.org/10.5194/egusphere-egu24-17028, 2024.

08:55–09:05
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EGU24-5816
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ECS
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On-site presentation
Meng Yao and Ronghua Kang

It has been recognized recently that trees can assimilate NO2 directly through leaf stomata. Both laboratory and field studies have measured the foliar NO2 deposition velocity, which could be determined by some environmental factors, e.g. light irradiation intensity, ambient NO2 concentration, and leaf characteristics. However, the NO2 uptake capacity and allocation of foliar uptake NO2 under these environmental factors remain unclear. To clearly understand the foliar NO2 uptake process and refine the forest NO2 uptake models, we conducted a dynamic 15NO2 fumigation experiment.

We selected Fraxinus mandshurica (F. mandshurica), Pinus koraiensis (P. konraiensis), Quercus mongolica (Q. mongolica), and Larix gmenilii (L. gmenilii) saplings, four dominant tree species in temperate forests of northeastern China, as our experimental materials. Meanwhile, we chose a pair of broad-leaved and coniferous tree species (F. mandshurica and P. konraiensis) to perform fumigation experiment under dark/light irradiation and another pair (Q. mongolica and L. gmenilii) to perform fumigation experiment with soil N addition. All saplings were dynamically fumigated with 50 ppb 15NO2 for 8 h and destructively sampled immediately after fumigation. We rinsed the samples surface with purified water, dried and grinded all samples, then measured the 15N abundance in leaves, twigs, stems and roots with EA-IRMS.

The results showed that tree saplings can absorb NO2 under both dark and light irradiation treatments. The total 15N recovery ranged between 30 to 80% under the light condition in all species. Under the dark condition, the total 15N recovery were (29.8±9.16) % and (1.1±0.47) % for F. mandshurica and P. konraiensis, which were significantly lower than under the light condition, (59.6±5.2) % and (8.8±2.5) %, respectively. With the soil N addition, the total 15N recovery in Q. mongolica ((56.2±8.8) %) were significantly larger than non-N addition ((27.6± 4.8) %), while L. gmenilii showed the opposite result that the total 15N recovery ((31.7±7.8) %) significantly decreased, compared to that without N addition ((73.6±4.3) %). These results are likely attributed to different amount of N demand for different tree species, more N needed for Q. mongolica than L. gmenilii. Moreover, coniferous species could assimilate more N through foliar uptake than broad-leaved species, probably due to bigger leaf surface areas of coniferous trees. After 8 h fumigation, the largest proportion of 15NO2 was recovered in leaves in all species and treatments, accounting for 60-97%, which indicates that NO2 stays in leaves in a short-term period after foliar assimilation. However, further studies are needed to explore the transformation of foliar incorporated NO2 to other organs in a long-term scale.

This study quantified the foliar NO2 uptake capacity of different tree species and figured out the effects of light irradiation and soil nitrogen availability on foliar NO2 uptake. Our results would provide references for the model estimation of canopy NO2 uptake magnitude at a regional scale.

How to cite: Yao, M. and Kang, R.: 2152, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5816, https://doi.org/10.5194/egusphere-egu24-5816, 2024.

09:05–09:15
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EGU24-17469
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On-site presentation
Michael Gundale, Kelley Bassett, Lars Östlund, Jonas Fridman, Steven Perakis, and Sandra Jämtgård

Boreal forests play an important role in the global carbon (C) cycle, and their productivity is strongly limited by nitrogen availability.  Thus, understanding whether nitrogen availability in boreal forests is changing has important implications for understanding past, present, and future trends of forest growth. We utilized a unique archive of tree cores collected by the Swedish National Forest Inventory, to evaluate temporal patterns (1950-2017) of wood δ15N, which is commonly used as an indicator of N limitation. First, we focused on an area of ca. 55,000 sq. km in central Sweden to evaluate how sensitive the wood δ15N approach is to tree age and two alternative sampling methodologies: a) analysis of single trees sampled in the present, versus b) tree chronologies constructed from multiple trees of the same age sampled during different decades.  By analysing 1038 woods samples, and covering two key boreal tree species (Picea abies and Pinus sylvestris), we found strong trends of declining δ15N through time, suggestive of progressive N limitation.  We further found that temporal patterns were highly sensitive to method choice, where the multiple tree approach supported by the tree core archive showed much stronger temporal patterns than reliance on more conventional contemporary sampling approaches, where N mobility appeared to obscure temporal patterns.  We further found that temporal trends were relatively insensitive to tree age class. Using the more powerful Multiple Tree Approach, we further evaluated δ15N values from an additional 1000 P. abies and P. sylvestris wood samples covering the entire forested area of Sweden and spanning the same time period, to investigate how temporal patterns in wood δ15N varied in areas with historically high N deposition (Southern Sweden) versus low N deposition (Northern Sweden).  These data help address current debates regarding whether temporal patterns in δ15N are indicative of oligitrophication (i.e. progressive N limitation), or are instead the result of changing δ15N signatures from nitrogen deposition inputs.  

How to cite: Gundale, M., Bassett, K., Östlund, L., Fridman, J., Perakis, S., and Jämtgård, S.: Evaluating temporal patterns in wood δ15N in Swedish forests as an indicator of changing N limitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17469, https://doi.org/10.5194/egusphere-egu24-17469, 2024.

09:15–09:25
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EGU24-15470
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On-site presentation
Wolfgang Wanek, Michaela Bachmann, Ye Tian, Steve Kwatcho Kengdo, Jakob Heinzle, Erich Inselsbacher, Werner Borken, and Andreas Schindlbacher

Climate warming was shown to strongly affect the biogeochemical cycles in global forests, reducing soil carbon storage and accelerating soil nitrogen (N) and phosphorus cycling. In a long-term soil warming experiment in a temperate old-growth forest in Achenkirch, Austria, we recently showed faster root turnover and growth, decreases in microbial biomass, carbon use efficiency and soil carbon storage, increases in ecosystem phosphorus limitation, and varied responses of the soil N cycle in warmed plots (+4 ° C above ambient for 14 years). In this study we therefore employed natural stable isotope techniques to better understand ecosystem-level responses of the N cycle in Achenkirch, studying the abundance of 15N and 14N (expressed as δ15N values) in a wide range of soil nitrogen pools (bulk soil N, root N, microbial biomass N, extractable organic N, ammonium, nitrate) and employed isotope fractionation models to explain the patterns found dependent on soil warming. Specific N cycle processes such as mineralization, nitrification and denitrification cause substantial isotope fractionation (against the heavy stable isotope 15N), leading to 15N enrichment of the residual substrates and 15N depletion of the cumulative products, depending on the fraction on substrates consumed and the isotope fractionation factor of that process. Other processes such as diffusion, (de)sorption and depolymerization exert negligible isotope fractionation. We found a significant warming effect on the isotopic signatures of root N and the soil ammoniumpool, i.e. a 15N enrichment in these pools. 15N enrichment of tree fine roots, considered to be isotopic integrators of the plant available N pool, suggest increased soil N cycling and greater soil N losses in warmed plots causing a 15N enrichment of the soil inorganic N pool (ammonium and nitrate). The increased 15N enrichment in ammonium of warmed soils highlights an increased activity of nitrifiers, with greater fractions of ammonium oxidized to nitrate causing the observed 15N enrichment of ammonium. However, soil nitrate did not show the expected 15N depletion imparted by nitrifiers but matched or even exceeded δ15N values of soil ammonium. Isotope fractionation calculations indicated that >50% of the soil nitrate produced was lost, particularly through denitrification promoting gaseous N losses in the form of NO, N2O and/or N2 and less through nitrate leaching. Natural 15N abundance studies thereby hold great potential for evaluating the status quo of the complex N cycle in terrestrial ecosystems and to monitor in situ responses to climate change with minimal invasion and improved time integration.

How to cite: Wanek, W., Bachmann, M., Tian, Y., Kwatcho Kengdo, S., Heinzle, J., Inselsbacher, E., Borken, W., and Schindlbacher, A.: Long-term soil warming causes acceleration of soil nitrogen losses in a temperate forest studied by 15N isotope fractionation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15470, https://doi.org/10.5194/egusphere-egu24-15470, 2024.

09:25–09:35
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EGU24-4706
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ECS
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On-site presentation
Chun Chung Yeung, Harald Bugmann, Frank Hagedorn, and Olalla Díaz-Yáñez

Current soil biogeochemical models have difficulties matching the observed composition of soil organic matter (i.e., the relative proportions of deadwood, raw litter, organic horizon, particulate organic carbon, and mineral-associated organic carbon). In reality, nitrogen (N) controls microbial decomposition and physiological processes, whereas in most models it is merely considered a plant nutrient. In addition, many N fertilization studies have shown that N exerts different effects on different C pools via changing exoenzyme activities, microbial growth, and necromass production via microbial turnover. These divergent effects control SOM composition and have C-cycle consequences.

We expanded the CENTURY model by incorporating multiple hypothesized microbial responses to nitrogen availability, including 1) decomposition reduction of recalcitrant substrates when N is in excess; 2) decomposition stimulation of high C:N substrates when N limitation is alleviated; 3) microbial adaptation of turnover rate; 4) microbial adaptation of CUE; and 5) secondary feedback to decomposition via changes in microbial biomass in response to N. We systematically tested multiple model variants using two sets of simulations, one along a natural N gradient in Swiss forests, and another one with artificially increased N input (i.e., simulating an N-fertilization experiment). We evaluated the simulated outputs using data on soil organic matter fraction stocks, their relative proportions, and temporal responses under N addition.

From the simulation results, we identified the necessary processes to explain the temporal response pattern of different C pools to N addition, in accordance with findings from meta-analyses. In addition, we identified patterns of SOM composition over a natural gradient of N supply (no artificial N addition), which can again be explained by the N-driven processes we implemented. We conclude that considering the direct effects of nitrogen as a key additional constraint on microbial processes is essential to improve the realism and accuracy of soil biogeochemistry models.

How to cite: Yeung, C. C., Bugmann, H., Hagedorn, F., and Díaz-Yáñez, O.: How does nitrogen control soil organic matter composition? – A theory and model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4706, https://doi.org/10.5194/egusphere-egu24-4706, 2024.

09:35–09:45
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EGU24-13239
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ECS
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On-site presentation
Maureen Beaudor, Elena Shevliakova, Sergey Malyshev, and Minjin Lee

Representing plant-microbe-soil organic matter interactions and their coupling with land surface processes are critical to understanding of ecosystem responses to climate change. More specifically, microbes play an important role in the nitrogen (N) cycle by providing acquisition pathways for plants and overcoming N limitation through mycorrhizal symbiosis and bacterial fixation. Even though biological nitrogen fixation acts as a primary N source for the organisms, ecosystem N availability is still strongly affected by N losses, including atmospheric volatilization.

One of the major challenges to accurately representing N availability in Earth System Models (ESM) is the representation of the atmospheric losses that are not necessarily controlled by the organisms. For instance, the conversion of soil ammonium into gaseous ammonia (i.e., volatilization) is driven by ambient environmental conditions and not directly controlled by the biological demand of plants and soil microbes. Thus, rapid losses of N via volatilization (e.g., after precipitation events) could induce feedback on soil microbial activity and plant growth by impeding biological assimilation.

Even though the representation of ammonia emissions is progressively integrated into ESMs, the focus has been mainly on parameterizing losses from agricultural or managed ecosystems. However, ammonia volatilization from natural soils occurs worldwide and can reach 9 TgN/yr, a non-negligible source, especially in alkaline drylands. Up to now, no proper representation of emissions of ammonia, applicable to unmanaged lands, has been included in ESMs and challenged by observations. In the future, these emissions are likely to follow the rising trends of nitrogen deposition and increasing precipitation due to climate change.

Here we describe a mechanistic parameterization of ammonia emissions in natural ecosystems with explicit treatment of microbes and vegetation dynamics in the fully integrated terrestrial component of the GFDL ESM, LM4.2-GIMICS-N. We apply observational constraints, including measurements of soil 15N isotope and estimates of nitrogen fluxes (BNF, nitrification, mineralization, and ammonia exchange) at different sites to reduce uncertainty in the model simulations. Finally, we examine the main drivers of ammonia volatilization across various ecosystems by considering aridity, soil pH, and nitrogen deposition as well as the key environmental conditions such as precipitation, temperature, and soil moisture.

How to cite: Beaudor, M., Shevliakova, E., Malyshev, S., and Lee, M.: Resolving nitrogen gaseous pathways in the atmosphere-plant-microbial-soil continuum in the NOAA/GFDL Earth System Modeling Framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13239, https://doi.org/10.5194/egusphere-egu24-13239, 2024.

09:45–09:55
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EGU24-12116
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On-site presentation
Rebecca M. Garland, Mogesh Naidoo, Katye Altieri, Phesheya Dlamini, Gregor Feig, Kerneels Jaars, Lerato Sekhohola, Pieter van Zyl, Nomsa Muthelo, Jabulile Leroko, Pelenomi Sakwe, Tamryn Hamilton, Tiaan van Niekerk, Pedro Bixirao Neto Marinho, and Kathleen Smart

The biogeochemical nitrogen (N) cycle in South Africa is influenced by, and in turn influences a number of crucially important global change processes. However, the natural N cycling in South Africa is not well-understood. The “Emissions, deposition, impacts - Interdisciplinary study of N biogeochemical cycling (EDI-SA)” project is working to improve our baseline understanding of the natural biogeochemical cycling of N in non-industrialized ecosystems across South Africa. This includes quantifying N fluxes from emissions through to deposition, identifying linkages between N cycling and related species such as sulphur (S) and ozone, and evaluating ecosystem impacts. Previous work has focused on the impact of atmospheric deposition of N and S species on ecosystems at sites almost exclusively on the industrialized Highveld. This has left large gaps of knowledge in the biogeochemical cycling and ecosystem impacts, particularly within the diverse natural ecosystems found across South Africa. In order to address this gap, EDI-SA is applying a more holistic approach using measurements (from two South African Research Infrastructures; EFTEON and BIOGRIP) and modelling to investigate multiple linkages within the biogeochemical cycling of N with a focus on improving the understanding of the natural cycling. The project is applying a variable resolution sampling approach to investigate processes which occur at multiple spatial scales, and applying multiple measurement techniques including atmospheric measurements, stable isotope analysis of aerosol particles, rainwater and soil, and analysis of soil chemistry and biology. This contribution will detail the approach of this interdisciplinary project, highlight results from the first soil and air sampling campaigns, as well as the atmospheric composition modelling that assesses the relative importance and impacts of N emissions from soil across South Africa. This baseline understanding will allow future research to assess the potential changes to N biogeochemical cycling into the future in a changing climate.  

How to cite: Garland, R. M., Naidoo, M., Altieri, K., Dlamini, P., Feig, G., Jaars, K., Sekhohola, L., van Zyl, P., Muthelo, N., Leroko, J., Sakwe, P., Hamilton, T., van Niekerk, T., Bixirao Neto Marinho, P., and Smart, K.: Examining the natural nitrogen biogeochemical cycling and impacts across South African ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12116, https://doi.org/10.5194/egusphere-egu24-12116, 2024.

09:55–10:05
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EGU24-5728
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ECS
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On-site presentation
Nathalie Ylenia Triches, Maija Marushchak, Anna Virkkala, Timo Vesala, Martin Heimann, and Mathias Göckede

Nitrous oxide (N2O) is one of the most important greenhouse gases with a global warming potential of about 298 times stronger than carbon dioxide (CO2) over a period of 100 years. From 1800 to 2023, the atmospheric concentration of N2O has increased from 273 to 336 ppbv, whereby more than half of this rise is due to the addition of fertilisers and manure on agricultural soils. Whilst these managed, nutrient-rich soils have been relatively well studied, little is known about N2O fluxes in nutrient-poor ecosystems (e.g., the Arctic).

Since many Arctic soils contain very low amounts of available nitrogen, in the past it has been generally assumed that Arctic soils are not a significant source of N2O. Only recently, several studies have reported significant N2O emissions from organic-rich Arctic soils; however, due to methodological challenges, extensive investigations on N2O fluxes in Arctic soils have been limited. As a result, the importance of N2O fluxes from this region to the global budget remains highly uncertain. 

With the recent advances in portable GHG analyser technology, extensive manual chamber measurements based on in-situ N2O concentration measurements can provide novel information to close this knowledge gap. However, guidelines on measuring techniques (e.g., chamber closure time) and data quality (e.g., no flux vs. low flux) are still lacking. In this study, we provide new insights on N2O fluxes in a nutrient-poor ecosystem and give general practical guidelines for measuring low N2O fluxes with a portable gas analyser and manual chambers. In May, July, and September 2023, we used a portable N2O/CO2 analyser to measure N2O fluxes in a thawing sub-Arctic permafrost peatland in northern Sweden. Recommendations on practical use in the field are given to support future N2O research with portable gas analysers. 

How to cite: Triches, N. Y., Marushchak, M., Virkkala, A., Vesala, T., Heimann, M., and Göckede, M.: Advances in measuring low N2O fluxes by a portable gas analyser and manual chambers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5728, https://doi.org/10.5194/egusphere-egu24-5728, 2024.

10:05–10:15
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EGU24-6942
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ECS
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On-site presentation
Biao Luo and Amos P. K. Tai

Chinese agriculture has long been characterized by low nitrogen use efficiency (NUE) associated with substantial ammonia (NH3) loss, which contributes significantly to fine particulate matter (PM2.5) pollution. However, the knowledge gaps in the spatiotemporal patterns of NH3 emissions and the states of nitrogen management of agricultural systems render it challenging to evaluate the effectiveness of different mitigation strategies and policies. Here we explored the NH3 mitigation potential of various strategies and its subsequent effects on PM2.5 pollution, and their effectiveness in improving NUE of Chinese agricultural systems. We developed and used a nitrogen flow model for evaluating NUE of different crop and livestock types at a provincial scale in China. We then used the bottom-up NH3 estimates to drive an air quality model (GEOS-Chem High Performance, GCHP) to provide an integrated assessment of four improved nitrogen management scenarios: improving NUE of crop systems (NUE-C), increasing organic fertilizer use (OUR), improving NUE of livestock systems (NUE-L) and combined measures (COMB). The total agricultural NH3 emission of China was estimated to be 11.2 Tg NH3 in 2017, of which 46.24% and 53.76% are attributable to fertilizer use and livestock animal waste, respectively, and emission hotspots can be identified in the North China Plain. Our results show that grain crops have higher NUE than fruits and vegetables, while high livestock NUE can be found in pork and poultry, and NUE for the entire crop and livestock systems are both better in Northeast China than the rest of China. We also found that agricultural NH3 emissions can be reduced from 11.2 Tg to 9.1 Tg, 9.3 Tg, 9.9 Tg and 6.8 Tg, and consequently annual population-weighted PM2.5 reductions are estimated to be 1.8 µg m–3, 1.6 µg m–3, 1.3 µg m–3 and 4.1 µg m–3 under NUE-C, OUR, NUE-L and COMB scenarios, respectively. Our results are expected to provide decision support policy making concerning agricultural NH3 emissions.

How to cite: Luo, B. and Tai, A. P. K.: Improving Agricultural Nitrogen Use Efficiency to Reduce Air Pollution in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6942, https://doi.org/10.5194/egusphere-egu24-6942, 2024.

Coffee break
Chairpersons: Tuula Larmola, Dianming Wu
Nitrogen cycling in agricultural and aquatic environments
10:45–10:55
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EGU24-5701
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ECS
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On-site presentation
Anina Gilgen, Simon Baumgartner, Ernst Spiess, and Frank Liebisch

For the agri-environmental monitoring of Switzerland, nitrogen balances on farm level for all Swiss farms were calculated and aggregated in order to obtain regionalized nitrogen balances. This monitoring attempts to incorporate as much existing data as possible to minimize multiple data collections from farmers. Data from the agricultural policy information system of Switzerland was used as basis for the calculation. This database contains information on livestock numbers, the crops grown, and the direct payments received for each farm. This information was supported with different data sources from federal offices, cantons, agricultural associations, and research institutions. Balances were calculated as a soil-surface balance according to the OECD method, which includes N input via organic and mineral fertilizers, biological N-fixation, atmospheric N-deposition, and seedlings as well as N outputs via plant yields.

The regional balances showed a high variability, resulting in an average N surplus of around 105 kg N per hectare of utilized agricultural area in cantons with highly intensive livestock farming and around 16 kg N in cantons with more extensive farming practices, i.e. in mountain regions. On national scale, highest N input occurred via organic fertilizers, whereas mineral fertilizers and biological N-fixation account for around 15% of the total input each.

Our approach of calculating N balances on farm level for the whole Swiss farming system has some limitations, which are mainly due to missing or incomplete data sources.  As an example, the use of mineral fertilizers had to be estimated by application data of a rather small sample of farms (~300 farms). Nevertheless, the obtained results show that this methodology is a promising tool to gain a regional overview of the environmental status of Swiss farms. Over the years, this approach will be refined and new data (e.g. additional administrative data, satellite data) can be incorporated in order to better estimate the N balances of Swiss farms.

How to cite: Gilgen, A., Baumgartner, S., Spiess, E., and Liebisch, F.: Regionalized nitrogen balances of Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5701, https://doi.org/10.5194/egusphere-egu24-5701, 2024.

10:55–11:05
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EGU24-20772
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Highlight
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On-site presentation
Nicolas Brüggemann, Kerui Zhao, and Rüdiger Reichel

One of the most pressing issues in intensive agriculture is how we can reduce post-harvest losses of nitrogen (N) on agricultural land. In terms of N use efficiency, the focus so far has been on optimizing the amount and timing of N fertilization, including spatially targeted application (precision agriculture). However, we must be aware that this will not be sufficient to solve the problem of N surplus. The mineralization of crop residues and soil organic matter, especially after harvest, can lead to very high mineral N concentrations in the soil, which ultimately result in high N losses, mainly in the form of nitrate leaching, but also as nitrous oxide (N2O) if the excess N is not immobilized before winter. In crop rotations that do not allow the cultivation of a catch crop, e.g. before winter cereals, the N immobilization potential is by far not high enough to immobilize the available mineral N. In this case, a different approach than plant N immobilization is required to immobilize the excess N before winter.

Here, we present results from laboratory incubations and field trials with different soils under a wide range of conditions based on the stimulation of microbial biomass growth by readily available organic soil amendments. They show that effective immobilization of mineral N in large quantities (almost 100 % reduction of nitrate concentration in the soil) is possible for several months, even under winter conditions. A consistent picture emerges from the results, suggesting that the optimal and longest-lasting effect of N immobilization can be achieved with nitrogen-free organic compounds that are moderately available to microorganisms (i.e., within several weeks rather than a few days). If the microorganisms are offered compounds that are too readily available (extreme case: glucose), a rapid stimulating effect can be triggered, which, however, does not last long enough to immobilize N for several months due to too early remineralization. If too recalcitrant organic compounds are introduced into the soil, the utilization of the additional carbon source takes too long to lead to effective N immobilization. We can therefore say that we have taken a significant step forward in understanding the mechanisms and timing of microbial N immobilization and remobilization, which may prove key to solving the N surplus problem in agriculture. However, the extent to which such management measures can be implemented in agricultural practice also depends on the political framework conditions that make them economically feasible.

How to cite: Brüggemann, N., Zhao, K., and Reichel, R.: How can we reduce post-harvest nitrogen losses on agricultural land? Evaluating the potential of easily degradable, nitrogen-free organic soil additives, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20772, https://doi.org/10.5194/egusphere-egu24-20772, 2024.

11:05–11:15
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EGU24-21470
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On-site presentation
Iris Karbon, Konstanze Madani, Judith Prommer, Paula Rojas, Andrew Giguere, Christopher Sedlacek, Taru Sandén, Heide Spiegel, Petra Pjevac, and Lucia Fuchslueger

High nitrification rates and substantial nitrogen (N) losses through nitrate leaching and N2O emissions make current agricultural practices unsustainable, contributing to greenhouse gas emissions and environmental pollution. Synthetic nitrification inhibitors (SNIs) can be amended with N-fertilizers to reduce the conversion of ammonia to nitrate by soil nitrifiers. SNIs aim to increase agricultural nitrogen use efficiency (NUE), but they have several disadvantages (e.g., costs, ineffectiveness in the field, possible accumulation in the food chain). The use of biological nitrification inhibitors (BNIs), naturally occurring in plant root exudates, could become an alternative to SNIs. Potential BNIs should be highly specifically targeting nitrification, but for most known BNIs it is unclear if and how they affect other soil microorganisms and biogeochemical processes.

This study aimed to investigate possible off-target effects of BNIs in agricultural soils. We tested the effect of two candidate BNIs (Methyl 3-(4-hydroxyphenyl)propionate and DL-limonene) in slurry assays on soil microbial communities from a typical Austrian agricultural field (Linz, pH 6.89±0.12, fertilized with 120 kg N ha-1 yr-1), and compared them to a known SNI (nitrapyrin), and two further nitrification inhibitors (phenylacetylene and octyne). The slurries were incubated for eight days and CO2 production, pH, as well as nitrate- and N2O accumulation were measured. At the end of the incubation, we analyzed fluorescence-based enzyme activity, as well as microbial substrate use efficiency using ‘Biolog©’ assays to test the influence on general microbial activity, selected microbial soil processes, and the effectiveness of nitrification inhibition, respectively.

Our results showed that both tested BNIs significantly reduced net nitrification rates, but also affected other biogeochemical processes, even though limonene lost some effectiveness during the incubation. MHPP was heavily respired by heterotrophic microorganisms, leading to a drop in pH and heterotrophic competition for the remaining ammonium, therefore likely acting as an indirect nitrification inhibitor. Extracellular enzymes were also affected: MHPP led to increased potential β-glucosidase activity, while nitrapyrin led to a decrease in potential phosphatase activity. General soil microbial substrate use diversity seemed to be unaffected by the input of either BNIs or SNIs. Whether or not the observed off-target effects are positive and what they mean for the large-scale application of BNIs in the agricultural industry remains to be further investigated.

How to cite: Karbon, I., Madani, K., Prommer, J., Rojas, P., Giguere, A., Sedlacek, C., Sandén, T., Spiegel, H., Pjevac, P., and Fuchslueger, L.: Off-target effects of biological nitrification inhibitors on soil microbial substrate use and enzyme activity in an agricultural soil , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21470, https://doi.org/10.5194/egusphere-egu24-21470, 2024.

11:15–11:25
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EGU24-17096
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ECS
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On-site presentation
Georgios Giannopoulos, Elpida Pasvadoglou, Georgios Kourtidis, Lars Elsgaard, George Zanakis, and Ioannis Anastopoulos

Under the framework of Circular Economy, EU Green Deal, and UN Sustainable Development Goals the addition of organic amendments to agricultural soils is highly promoted as a cost-efficient solution to improve soil quality and agrosystem sustainability. Nonetheless, their agronomic use comes with an uncertainty of their potential to release ample plant-available N, and to emit soil greenhouse gases.

This mesocosm study investigated short-term (90 d) soil N dynamics of a loamy soil receiving four organic amendments (50 t ha-1) (i) cow manure compost (CMC), (ii) food waste compost (FWC), (iii) used digestate substrate (UDS) and (iv) municipal sewage sludge (MSS), without and with N fertilization (160 kg N ha-1; urea). An unamended soil mesocosm was included as a control (C). During the incubation soil NO2-, NO3-, NH4+, N2O and CO2 were regularly monitored.

During the incubation, org. amendments did not affect NH4+ availability (AUC) compared to unamended soil, except MSS treatment which had 5.7x more NH4+ than C. The co-application of urea increased available NH4+ by 2.9x, 4.1x, 4.4x, 4.6x, and 5.9x for MSS, UDS, CMC, FWC, and C, respectively. There was no difference in available NO2- among org. amendment treatments and the C, except MSS (2.4x). There was a substantial and temporal accumulation of NO2- (2.4x to 3.6x) when urea was co-applied with org. amendments. Co-application of urea with org. amendments increased AUC NO3- in all treatments ranging to 2.7x from 13.6x, except MSS. Considering cum. CO2 we did not observe any differences between org. amended treatments without and with urea. However, org. amendments increased cum. N2O emission by 1.4x, 1.6x, and 3x, for UDS, FWC, and MSS, and reduced by 0.6x for CMC relative to C, respectively. The co-application of urea increased cum. N2O emissions for MSS, UDS, and CMC by 6%, 65%, and 90%, respectively, and reduced by 58% for FWC, compared to the corresponding org. treatment without urea.

Interestingly, co-application of urea with org. amendments reduced N2O emission factor (EF) by 4x, 6x, 6x, and 9x, relative to org. amendments without urea, for CMC, MSS, UDS and FWC, respectively. However, the EF N2O exceeded 1% in most cases. Treatments with urea lost substantial amounts of org. C as CO2-equivalent emissions, for instance, UDS+U and MSS+U lost 22% and 68%, respectively.  

In conclusion, our preliminary results indicate that the co-application of org. amendments with urea-N could potentially fuel soil N2O emissions, thus offsetting any favorable aspects of the aforementioned policies. Org. amendment, urea-N, and their interaction were significant factors (p≤0.05) driving CO2 and N2O emissions. The quality and composition of the amendments may stimulate soil microbial N transformations, and further investigation will elucidate the intrinsic role of soil microbes and their dynamics in regulating CO2 and N2O emissions from soils.

The research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers”; Project #01053 awarded to P.I. Dr Georgios Giannopoulos. This project was co-implemented with industrial partner Corteva Agriscience Hellas SA.     

How to cite: Giannopoulos, G., Pasvadoglou, E., Kourtidis, G., Elsgaard, L., Zanakis, G., and Anastopoulos, I.: Co-application of organic amendments and urea-N in a loamy soil reduced the N2O emission factor but substantial amounts of organic C were lost as CO2., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17096, https://doi.org/10.5194/egusphere-egu24-17096, 2024.

11:25–11:35
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EGU24-19499
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ECS
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On-site presentation
Johannes Friedl, Daniele De Rosa, Clemens Scheer, Michael Fitzgerald, Peter R. Grace, and David W. Rowlings

Intensively managed pasture systems receive large inputs of nitrogen (N) in the form of fertiliser and through the  deposition of ruminant urine, creating hot-spots for denitrification which results in variable amounts of nitrous oxide (N2O) and dinitrogen (N2) emitted. Here we investigated the potential of increased  irrigation frequency to reduce N2O and N2 emissions from an intensively managed pasture in the subtropics after ruminant urine deposition. Irrigation volumes were estimated to replace evapotranspiration and were applied either once (Low-Frequency) or split into four applications (High-Frequency). This irrigation schedule was applied 3 times over the 60 day monitoring period, and fluxes of N2O and N2 were  measured using the 15N gas flux method. In line with farming practice, simulated urine patches (equivalent of 80 g N m-2 applied) were also fertilised three times with 2 g urea N m-2 to show the combined effects of urinary and fertiliser N on N2O and N2 emissions. Highest N2O emissions of up to 60 mg N2O-N m-2 day-1 were observed briefly after urine deposition, decreasing thereafter, resulting in cumulative N2O losses of 169.9 mg N2O-N m-2 from the Low-Frequency treatment. Denitrification was dominated by N2, accounting for more than 89% of  N2O+N2 emitted. Irrigation treatments had no effect on cumulative N2 losses of more than 2700 mg N2-N m-2. However, High frequency irrigation reduced cumulative N2O losses by 35%. Our findings suggest that under conditions of high N availability, increased irrigation frequency can reduce the environmental impact (N2O) of denitrification, but not overall N losses via this pathway. The response of N2O emissions may further indicate that less frequent, but more intense rainfall events will shift the product ratio of denitrification towards N2O, increasing environmentally harmful N losses from intensively managed pasture systems.

How to cite: Friedl, J., De Rosa, D., Scheer, C., Fitzgerald, M., Grace, P. R., and Rowlings, D. W.: Increased irrigation frequency reduces N2O, but not overall denitrification losses (N2O+N2) from an intensively managed pasture following ruminant urine deposition and nitrogen fertilisation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19499, https://doi.org/10.5194/egusphere-egu24-19499, 2024.

11:35–11:45
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EGU24-4369
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ECS
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Virtual presentation
Gianni Micucci, Fotis Sgouridis, Stefan Krause, Iseult Lynch, Niall P. McNamara, Felicity Roos, Leake Jonathan, and Sami Ullah

In this study, we aimed to constrain and characterize the dynamics of denitrification in three different fields: one conventional arable and two types of pasture (“leys”). During a one-year field campaign, denitrification was measured using our newly developed method combining the application of 15N tracer and artificial atmosphere for the incubation of soil cores under field conditions (Micucci, 2022), while total N2O emissions were measured using static flux chambers during parallel incubations. Our objectives were to determine the best way to upscale soil core denitrification measurements and trace the fate of applied synthetic nitrogen fertilizer via denitrification in conventional agriculture in comparison to pastures under regenerative agriculture practices.

We determined that the best way to derive field-scale fluxes of denitrification was to use the core method to calculate the source partitioning coefficient (SPC) and product ratio (PR) and use these metrics in combination with static chamber data. The SPC is defined as the proportion of total N2O emissions that originates from denitrification while the product ratio measures the proportion of denitrification product emitted as N2O rather than N2.

During the field campaign, we estimated that 22 kgN ha-1 were lost via denitrification in the arable field, amongst which 15.17 were attributed to fertilizer application, representing around 8% of the 200 kgN ha-1 applied. Furthermore, 9 % of the denitrified fertilizer was emitted as N2O rather than N2. On the other hand, the unfertilized ley emitted only 2.6 kgN ha-1 via denitrification annually. Overall, the total N2O emissions in the fertilizer arable field were responsible for around 2 t eqCO2 ha-1 year-1 compared to 0.15 in the unfertilized ley, highlighting the importance of land management in strategies of greenhouse gas emission reduction.

How to cite: Micucci, G., Sgouridis, F., Krause, S., Lynch, I., McNamara, N. P., Roos, F., Jonathan, L., and Ullah, S.: Constraining the denitrification process in conventional and regenerative agriculture, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4369, https://doi.org/10.5194/egusphere-egu24-4369, 2024.

11:45–11:55
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EGU24-12647
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On-site presentation
Stefan Werisch, Tiedke Alexandra, and Burghardt Diana

Nitrogen is a fundamental plant nutrient and the most important fertilizer in modern agriculture. At the same time nitrate based nitrogen loss from agroecosystems becomes an increasing environmental problem in ground- and surface waters. The lysimeter station Brandis in Saxony, Germany, provides detailed observations of water and solute fluxes under representative agricultural landuse since 1981. Despite substantial efforts and success in regulation and assessment of fertilizer needs and the reduction of fertilization excess, the seepage water analysis reveals increasing or stagnating levels of nitrate concentration in groundwater recharge in a broad range of soil types. This apparent decoupling between input and output is evident in all soil types under investigation and raises some important questions concerning the nitrate loss in agricultural soils:

  • Which part of the soil N-cycle contributes to the seepage water nitrate export?
  • What are the main drivers of nitrate loss in agricultural soils?
  • Can residence times of mineral fertilizer nitrogen be estimated?
  • Will reduced fertilization excess lead to timely reductions in nitrate loss to the groundwater?

We investigated these questions with long-term solute balances and state-of-the-art isotope methods. Analysis of source δ 15N ratios in soil, atmospheric deposition and fertilizer in combination with a 5-year campaign of δ15N and δ18O analysis of seepage water nitrate allows a source identification with dual-isotope plots and mixing models. The results clearly show that the main source of nitrate loss with the seepage water is the soil organic matter pool in all investigated soils. Analysis of the long-term nitrogen balances and the soil samples show furthermore a substantial accumulation of fertilization excess within the upper meter of agricultural soils and indicate that the residence time of nitrogen in the lysimeters might be substantially longer than water residence times. Isotope analysis in combination with mixing model analysis suggest that the nitrate loss is mainly driven by nitrification of this nitrogen legacy in the post-harvest period. Thus, the results hold an explanation why the current regulation efforts have not yet led to the desired reductions in nitrogen loadings of seepage water fluxes. Furthermore, the apparent decoupling between nitrogen input in agricultural soils and the seepage water output makes a timely reduction of nitrate concentrations, by reductions in fertilization excess alone, in groundwater recharge unlikely.

How to cite: Werisch, S., Alexandra, T., and Diana, B.: Insights into nitrogen dynamics and nitrate loss from agricultural soils based on long-term lysimeter observations and a 5-year isotope measurement campaign, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12647, https://doi.org/10.5194/egusphere-egu24-12647, 2024.

11:55–12:05
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EGU24-20301
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ECS
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On-site presentation
Carlos Palacin-Lizarbe, Stefan Bertilsson, Henri J. Siljanen, Moritz Buck, Lukas Kolh, Dhiraj Paul, Marion Maréchal, Hannu Nykänen, Tong Liu, Mikko Kiljunen, Sanni L. Aalto, Antti J. Rissanen, Christina Biasi, Anssi Vainikka, and Jukka Pumpanen

There is limited knowledge on the N (nitrogen) cycling in winter, on the role of organic matter quality on N cycling, and on the microbes involved.

We studied Lake Viinijärvi and Lake Höytiäinen, large boreal lakes in Finland, each lake with clear-water and brown-water sides. Viinijärvi has an additional side affected by mining activities in the catchment showing higher nitrate and sulphate levels. During winter of 2021 we sampled 5 sites at the beginning and at the end of the ice-covered period. Using the Isotope Pairing Technique we incubated sediment cores with 15NO3- and quantified the products of 1) complete denitrification (N2), 2) truncated denitrification (nitrous oxide, N2O), and 3) dissimilatory nitrate reduction to ammonium (DNRA, NH4+) to infer the process rates. We characterized the DOM using FT-ICR MS. We explore the genetic potential (DNA) of the sediment microbiome by using several sequencing techniques.

During winter the sediment-water interface is an active compartment. The top sediment microbiome has heterotrophic bacteria with flexible metabolism, breaking-down OM during winter despite most of the DOM is recalcitrant. Impacts of browning and mining with major differences between sites. The genetic potential of the sediment microbiome indicates more DNRA and N2O consumption in clear-waters, while in the mining-impacted site and brown-water sites the dominant pathway depends on the sediment layer with truncated denitrification in top layer, and methanogenesis and N-fixation in sub-top layer. The N2O production (d14), that fits the genetic potential, is highest in the mining-impacted site (35-43 µmol N/m2/d), followed by the brown-water sediments (6-11 µmol N/m2/d), with the lowest rates in the clear-water sediments (0-1 µmol N/m2/d).

How to cite: Palacin-Lizarbe, C., Bertilsson, S., Siljanen, H. J., Buck, M., Kolh, L., Paul, D., Maréchal, M., Nykänen, H., Liu, T., Kiljunen, M., Aalto, S. L., Rissanen, A. J., Biasi, C., Vainikka, A., and Pumpanen, J.: Browning and mining increase the nitrous oxide production in sediments of large boreal lakes during winter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20301, https://doi.org/10.5194/egusphere-egu24-20301, 2024.

12:05–12:15
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EGU24-5161
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ECS
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On-site presentation
Weikun Li, Xia Wang, Zhongyi Zhang, Xiaodong Liu, and Lei Geng

Atmospheric deposition of natural and anthropogenic sourced reactive nitrogen (Nr, mainly including NH3, NH4+, NOx, NO3- and etc.) has substantial influence on terrestrial and aquatic ecosystems, driving global nutrient imbalances and increasing risks to human health. Although it has been demonstrated that atmospheric Nr deposition has a substantial impact on nitrogen pools in remote and/or sensitive lakes, there is a scarcity of systematic evaluations regarding atmospheric Nr deposition's impact on the nitrogen burden in eutrophic lakes with riverine input as the primary source. Utilizing a regional chemical transport model, combined with observations of riverine nitrogen input, we investigate the contribution of atmospheric Nr deposition to a eutrophic Lake Chaohu in eastern China. The results indicate that riverine total nitrogen (TN) input to the lake was 11553.3 t N yr-1 and atmospheric TN deposition was 2326.0 t N yr-1 in the year of 2022. For Nr species which are directly available for the biosphere supporting algae and plant growth, riverine NH4+ input was 1856.1 t N yr-1 and atmospheric NHx (NH3 and NH4+) deposition was 824.5 t N yr-1. The latter accounts for ~ 1/3 of total NHx input to the lake. For NOy (HNO3 and NO3-) species, atmospheric deposition was estimated to also contributes a similar amount to the NHx species. The results suggest that even in regions with dense human activities with primary riverine N input, atmospheric deposition of Nr could also contribute significantly to the bio-available nitrogen in lake systems, and addressing eutrophication in Lake Chaohu and other eutrophic lakes will also need to consider the reduction of NH3 and NOx (i.e., NO + NO2, the precursor of NOy) emissions, in addition to the mitigation of riverine N input.

How to cite: Li, W., Wang, X., Zhang, Z., Liu, X., and Geng, L.: On the Contribution of Atmospheric Nitrogen Deposition to Nitrogen Burden in an Eutrophic Lake in Eastern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5161, https://doi.org/10.5194/egusphere-egu24-5161, 2024.

12:15–12:25
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EGU24-16147
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On-site presentation
Anders Fredenslund, Konstantinos Kissas, and Charlotte Scheutz

Direct emission of the greenhouse gases methane and nitrous oxide (N2O) constitute a significant fraction of the overall carbon footprint of wastewater treatment. Measurement methods to identify emission sources and to quantify emissions are key in mitigating these direct emissions. Nitrous oxide is formed in biological nitrogen removal process units, which are the main source of N2O emission from wastewater treatment.

Liquid phase sensors (LPS) have recently been developed and installed at various Danish wastewater treatment plants to measure N2O concentrations in the liquid phase of biological nitrogen removal tanks. These sensors can be used to implement adjustments on the operation of the plant (for example duration of aeration), which affects N2O emission. In addition, LPS can be utilized to calculate N2O emission through mass transfer modelling. However, there is a need for validation of liquid-based modelled emission rates against measurement methods, which measure direct N2O emission rates. In this study, emission rates determined by two remote sensing methods, the tracer gas dispersion method (TDM) and Eddy covariance method (EC) were compared to LPS derived N2O emission rates.

TDM relies on continuous, controlled release of a gaseous tracer at the source combined with downwind measurements of concentration of target gas (N2O here) and tracer gas (often acetylene - C2H2).  This method is well-established, validated, and has been used to quantify fugitive emissions from various sources such as landfills, composting plants, biogas plants, etc. EC is a stationary method, which relies on high-frequency measurements of N2O concentration and wind vector on a tower near the source. EC can be set up for continuous monitoring, while TDM as applied here is a discrete measurement method.

In the study, N2O emission rates were measured over a period of 1.5 years at a relatively large wastewater treatment plant in the greater Copenhagen area. TDM measurements were conducted on 15 measurement days covering both periods of relatively high and low N2O emission rates. TDM measurements were compared to LPS derived emission rates, where N2O emission was measured using sensors in four of eight process units for biological nitrogen removal. Overall, daily average emission rates between approximately 0.38 and 13.4 kg N2O h-1 were measured. High emission rates of 120 kg N2O h-1 were observed on a day, where plant maintenance is believed to be the cause of unusual high emission. Emission rates from simultaneous TDM measurements and LPS derived values (n=43) showed good correlation (R2=0.70). On average, emission rates from TDM were 35% higher than LPS rates. The model implementation to derive LPS determined emission rates was further developed during the study, and the listed results were the final values after some correction. Several factors can explain the difference – including liquid sensor drift, which for the specific sensors tends towards lower N2O concentration readings than actual concentrations. Continuous EC measurements showed the same emission dynamics as measured by the liquid sensors located inside the footprint of the station.

How to cite: Fredenslund, A., Kissas, K., and Scheutz, C.: Comparison of liquid phase and remote sensing measurements of nitrous oxide emission from biological nitrogen removal at a wastewater treatment facility, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16147, https://doi.org/10.5194/egusphere-egu24-16147, 2024.

12:25–12:30

Posters on site: Tue, 16 Apr, 16:15–18:00 | Hall X1

Display time: Tue, 16 Apr, 14:00–Tue, 16 Apr, 18:00
Chairpersons: Peter Dörsch, Sami Ullah
X1.1
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EGU24-9564
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ECS
Bin Wei and Yuanhe Yang

Nitrogen (N) plays an important role in mediating many aspects of permafrost carbon cycle, such as plant productivity, soil organic matter decomposition and the production of greenhouse gases. In contrast to the well-recognized effects of climate warming on soil organic carbon stocks and vulnerability, the fates and pools of soil N has received little attention in permafrost ecosystems.

Here, based on a decadal warming experiment in a permafrost ecosystem on the Tibetan Plateau, we assessed changes in soil N stocks over a 10-year time-scale, and in situ measured the majority of N-cycling processes involving biological N fixation and soil N transformation, and the preferential plant uptake of different N forms, and above- and belowground litter decomposition and N release, and N leaching losses as well as high-resolution nitrous oxide (N2O) flux during the growing season.

Our results showed that experimental warming progressively reduced topsoil N stocks but had no effect in the deeper soils on a 10-year time-scale. The observed decline in topsoil N pools could be due to the fact that decadal warming enhanced plant N uptake and intensified N leaching and gaseous losses. Specifically, warming treatment had a negligible effect on ecosystem biological N fixation rate, but increased the above- and belowground plant N pools. Meanwhile, simulated warming accelerated belowground litter N release and soil N transformation rate, and enhanced plant uptake of organic N. However, warming intensified the topsoil inorganic N leaching losses and N2O flux during the growing season.

These findings highlight that progressive N limitation could occur in permafrost ecosystems under continuous climate warming due to the re-allocation of N pool from soils to plants and the losses of N through leaching and gases flux, which would make the future trajectory of permafrost carbon cycle and its feedback to climate warming more complex than previously thought.

How to cite: Wei, B. and Yang, Y.: Progressive decline in topsoil nitrogen pool upon decadal warming in a permafrost ecosystem, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9564, https://doi.org/10.5194/egusphere-egu24-9564, 2024.

X1.2
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EGU24-2749
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ECS
Libin Wu, Ming Sheng, Xiaodong Liu, and Pingqing Fu

Organic nitrogen (ON) is an important participant in the Earth’s N cycle. Previous studies have shown that penguin feces add an abundance of nutrients including N to the soil, significantly changing the eco-environment in ice-free areas in Antarctica. To explore the molecular transformation of ON in penguin guano-affected soil, we collected guano-free weathered soil, modern guano-affected soil from penguin colonies, ancient guano-affected soil from abandoned penguin colonies, and penguin feces from the Ross Sea region, Antarctica, and Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) was used to investigate the chemical composition of water-extractable ON. By comparing the molecular compositions of ON among different samples, we found that the number of ON compounds (>4,000) in weathered soil is minimal, while carboxylic-rich alicyclic-like molecules (CRAM-like) are dominant. Penguin feces adds ON into the soil with > 10,000 CHON, CHONS and CHN compounds, including CRAM-like, lipid-like, aliphatic/ peptide-like molecules and amines in the guano-affected soil. After the input of penguin feces, macromolecules continue to degrade, and other ON compounds tend to be oxidized into relatively stable CRAM-like molecules, this is an important transformation process of ON in guano-affected soils. We conclude the roles of various forms of ON in the N cycle are complex and diverse. Combined with previous studies, ON eventually turns into inorganic N and is lost from the soil. The lost N ultimately returns to the ocean and the food web, thus completing the N cycle. Our study preliminarily reveals the molecular transformation of ON in penguin guano-affected soil and is important for understanding the N cycle in Antarctica.

How to cite: Wu, L., Sheng, M., Liu, X., and Fu, P.: Molecular transformation of organic nitrogen in Antarctic penguin guano-affected soil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2749, https://doi.org/10.5194/egusphere-egu24-2749, 2024.

X1.3
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EGU24-15243
Marketa Stepanova, Martin Novak, Bohuslava Cejkova, Frantisek Buzek, Ivana Jackova, Eva Prechova, Frantisek Veselovsky, and Jan Curik

Microbial N2-fixation helps to sustain carbon accumulation in pristine peatlands and to remove CO2 from the atmosphere. Recent work has provided evidence that this energetically costly process is not completely downregulated at sites with higher availability of reactive nitrogen (Nr). We studied nitrogen (N) cycling at three high-elevation, mainly rain-fed, Sphagnum-dominated peat bogs in the northern Czech Republic receiving medium to high amounts of reactive nitrogen (Nr) via atmospheric deposition. 15N/14N isotope ratios were determined in Nr deposition, along vertical peat profiles, and in a laboratory incubation study using fresh Sphagnum and 15N-enriched atmospheric N2. Our objective was to assess the potential for biological N2-fixation at the selected study sites in light of various biogeochemical parameters. Historically, all the peat bogs experienced similar changes in atmospheric Nr (mainly NO3--N and NH4-N) inputs. Nr depositions at all three sites peaked between 1980 and 1990. During that time period, the highest annual depositions were close to 10 kg ha-1 yr-1 at the slightly more polluted site Uhlirska (UHL) than at Male mechove jezirko (MMJ) and Brumiste (BRU). Since ca. 1990, atmospheric deposition of Nr has been steadily decreasing. Living Sphagnum had variable N concentrations with similar means for all three sites (1.1, 1.0 and 0.9 wt. % at MMJ, BRU and UHL, respectively). Downcore, peat density remained nearly constant at MMJ but increased at BRU and UHL. Ash contents were below 10 wt. % at least to the depth of 20 cm. With an increasing peat depth, both N concentration and δ15N values generally increased, while C/N ratios tended to decrease. At depths > 10 cm, N/P ratio was lower at UHL than at the other two sites and remained nearly constant downcore. N/P ratio at MMJ increased from ~10 to ~20 with an increasing depth, whereas the N/P ratio exhibited a zigzag vertical pattern at BRU, reaching a value of 40 in deeper segments. The potential for biological N2-fixation was investigated using a replicated laboratory incubation of fresh Sphagnum in a closed system following an application of 98 % enriched atmospheric N2. The experiment lasted for 7 days. The control Sphagnum samples had δ15N values of -4.0 ‰ (BRU and UHL) and -3.7 ‰ (MMJ). At the end of the incubation, the δ15N significantly increased only in MMJ moss reaching + 70 ‰, while it remained unchanged in BRU and UHL moss. Biological N2 fixation was thus recorded at only at MMJ, a site with the lowest N/P ratio in the topmost 2-cm thick sections. Potential N2 fixation rates at MMJ were similar to values previously reported for Finland (Leppänen et al. 2015) but ~7 times lower than at sites located in Patagonia, Chile (Knorr et al. 2016).

References

Leppänen et al., 2015. Plant and Soil, 389, 185-196.

Knorr et al., 2016, Global Change Biology 21, 2357–2365.

How to cite: Stepanova, M., Novak, M., Cejkova, B., Buzek, F., Jackova, I., Prechova, E., Veselovsky, F., and Curik, J.: A Sphagnum incubation study using 15N-labelled atmospheric N2 reveals contrasting potential for biological N2 fixation at three medium-polluted Central European peat bogs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15243, https://doi.org/10.5194/egusphere-egu24-15243, 2024.

X1.4
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EGU24-5244
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ECS
Devon Collier-Woods, Sami Ullah, and Sophie Comer-Warner

Saltmarshes have the potential to sequester large amounts of carbon, however, the value of stored carbon may be partially offset by emissions of the potent greenhouse gas nitrous oxide (N2O). Increased nutrients [NO3- and NH4+] have been shown to increase N2O emissions from saltmarshes, however, a global-scale analysis of this relationship has not been performed. Here, we present a global meta-analysis to investigate the relationship between N2O fluxes and porewater nitrogen and determine the relative importance of porewater NO3- and NH4+ as key drivers of enhanced saltmarsh N2O fluxes. Both porewater NO3- and NH4+ were significantly, positively correlated with N2O fluxes (p < 0.01), explaining 25 and 18% of the variation in fluxes, respectively. We estimate a global saltmarsh N2O flux of 0.012 Tg N2O yr-1, which is six times higher than the current estimate (0.0021 Tg N2O yr-1), representing an offset of 19% of the estimated global saltmarsh carbon burial. Using predicted future increases in riverine DIN export, our meta-analysis suggests that 17-31% of the estimated global saltmarsh carbon burial could be offset by a surge in N2O emissions under chronic mineral N pollution. This meta-analysis indicates the importance of reducing nutrient inputs into saltmarshes to reduce N2O fluxes and maximise their negative radiative forcing.

How to cite: Collier-Woods, D., Ullah, S., and Comer-Warner, S.: Surges in global N2O fluxes from saltmarshes are driven by increasing porewater nitrate and ammonium concentrations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5244, https://doi.org/10.5194/egusphere-egu24-5244, 2024.

X1.5
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EGU24-2534
Sami Ullah, Megha Kaviraj, Yafei Guo, Gianni Micucci, and Fotis Sgouridis

Rice uses 34-43% of the global irrigation water and is responsible for the usage of 24-30% of the world's total freshwater. More than 75% of rice produced in India is cultivated using the traditional continuous flooding (CF) irrigation method, which is a labour-intensive, time, water and energy-consuming process and a key source of global methane emissions. Alternate Wetting and Drying (AWD) is a popular water-saving approach trailed in Asia including India to reduce water use and methane emissions, whilst sustaining rice production. AWD is a method of periodic soil saturation followed by drying compared to CF. The objective of this research was to evaluate greenhouse gas (GHG) fluxes and internal and external nitrogen cycling processes as influenced by AWD and CF management regimes. A mesocosm experiment was set up in the laboratory using imported Indian paddy soil where Jasmine rice (var KDML 105) was grown. Our results depicted that plant biomass (52.57%), root biomass (28.57%), height (24.77%), effective tiller number (45.15%), stem sheath diameter (53.38%) and stomatal conductance (66.49%) were significantly (p<0.05) higher in CF compared to AWD treatment. A similar trend was observed in rice leaf chlorophyll (Chl a, b and total chl) contents. Interestingly, the chlorophyll a and b ratio observed was higher (1.63) in AWD compared to CF (1.03) conditions. This was likely during the process of chlorophyll b degradation and conversion to Chl a, thus resulting in the increase of a to b ratio to cope with the stress by maintaining the leaf photosynthetic efficacy. Soil enzyme activity revealed that β-glucosidase (BG), β-N-acetyl-glucosaminidase (NAG), and acid phosphatase (AP) were higher in AWD, whereas leucine aminopeptidase (LAP) activity was significantly higher in CF. Higher LAP activity might be a response to limited nutrient availability, as LAP helps to release amino acids that serves as a source for N mineralization and N supply. The 15N isotope tracing study revealed that denitrified N2O flux was significantly (p<0.05) higher in CF compared to AWD where source partitioning (% N2O denitrified) was 99.32% in CF and 27.01% in AWD. Higher gross mineralization was observed under AWD (3.92 ± 0.31µg-1 g-1 d-1) due to the promotion of aerobic microbial activity compared to CF (1.31 ± 0.31µg-1 g-1 d-1). A similar trend was observed for the consumption and immobilization of NH4+ and gross nitrification rates. GHG emissions rate viz., CH4-C, CO2-C, and N2O-N emissions were significantly higher under CF by 61, 3 and 72.%, respectively. Moreover, the global warming potential projected was higher under CF averaging at 10.92 mg kg-1 soil compared to 2.19 mg COkg-1 soil under AWD. Reduced GHG emissions under AWD provides for a significant negative feedback to global warming potential and future initiatives should keep emphasizing the optimization of this practice for its significant contribution to both climate change mitigation and sustainable agriculture.

How to cite: Ullah, S., Kaviraj, M., Guo, Y., Micucci, G., and Sgouridis, F.: Rice cultivation under continuous flooding vs alternate wetting and drying: implications for biomass, nitrogen cycling and greenhouse gas flux, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2534, https://doi.org/10.5194/egusphere-egu24-2534, 2024.

X1.6
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EGU24-2236
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ECS
Li Li and Xiao Liu

Biogenic volatile organic compounds (BVOCs) are carbon compounds released by plants through secondary metabolism. In the global background of nitrogen (N) deposition, plants respond to environmental changes by altering BVOCs and photosynthetic strategies. However, there is very little research on the release and photosynthetic characteristics of BVOCs in bamboo in response to N deposition. Therefore, we took Pleioblast amarus as a research object and conducted pot experiments to set up four different nitrogen deposition levels (referred to as "N deposition") (0 kg N hm-2-a-1(N0), 30 kg N hm-2 a-1(N1), 60 kg N hm-2 a-1(N2), and 90 kg N hm-2 a-1(N3)) to explore the effects of different N deposition levels on the release and photosynthetic characteristics of BVOCs in leaves, and analyzed the correlation between the indicators. The results showed that: (1) the percentage of isoprene emission from Pleioblast amarus bamboo leaves increased with the increase of N deposition level (significantly positively correlated), but the N deposition level did not significantly affect the total number of BVOCs; (2) the increase of N deposition level significantly increased the net photosynthetic rate and isoprene (ISO) emission rate of leaves, with the highest ISO emission rate under N3 treatment, which was 80. 39%, 75.07%, and 50.84% higher than N0, N1, and N2, respectively; (3) ISO emission rate and total BVOCs emission of Sanming bitter bamboo were significantly positively correlated with net photosynthetic rate and photosynthetic effective radiation of leaves, but ISO emission rate and total BVOCs emission were significantly negatively correlated with chlorophyll b and total chlorophyll content (P≤0.05). In conclusion, the increase in nitrogen deposition led to a remarkable increase in isoprene emissions from Sanming bitter bamboo leaves. 

How to cite: Li, L. and Liu, X.: Effects of nitrogen deposition on volatile organic compounds composition, isoprene emissions and photosynthetic characteristics of Pleioblast amarus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2236, https://doi.org/10.5194/egusphere-egu24-2236, 2024.

X1.7
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EGU24-10360
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ECS
Jaqueline Stenfert Kroese, Caroline Buchen-Tschiskale, Johannes Cordes, Rene Dechow, Klaus Dittert, Bryan Dix, Kathrin Fuchs, Andreas Gattinger, Jörg-Michael Greef, Balazs Grosz, Michael Hauschild, Jarrah Mahboube, Johannes Kühne, Henrike Mielenz, Thade Potthoff, Clemens Scheer, Franz Schulz, Conor Simpson, Benjamin Wolf, and Reinhard Well

The joint project 'Measures to reduce direct and indirect climate-impacting emissions caused by denitrification in agricultural soils - MinDen' addresses the topics of reducing nitrous oxide emissions and improving nitrogen efficiency through modeling, the evaluation of possible mitigation measures and the evaluation of denitrification on spatial scale. Gaseous emissions from denitrification cause N losses relevant to crop cultivation and cause direct N2O emissions from crop cultivation. Climate protection measures in crop production in the areas of fertilization, soil cultivation and crop rotation have hardly been researched with regard to the role of denitrification. Crop management that optimizes N efficiency and minimizes N emissions at the same time has therefore not yet been reliably defined. The overall objective of the present project is to identify practicable crop management measures to minimize N2 and N2O emissions from denitrification for arable cropping systems in Germany by improving the knowledge on denitrification-related N losses through field and laboratory studies and using it for parameterization, validation and application of simulation models. Our objectives are as follows:

  • Regionalization of N losses due to denitrification in Germany based on existing models
  • Determination of the effect of crop protection measures on N2 and N2O losses on field scale
  • Testing of mitigation options on the model, laboratory and field scale, taking into account the topsoil and subsoil for different soils
  • Further development of denitrification models to improve the mapping of mitigation measures using existing and new field data
  • Testing of mitigation options for Germany using the improved models, taking into account yield, economic efficiency, technology requirements, N2O emissions, N efficiency, fertilizer requirements, NH3 emissions and nitrate leaching.

We provide an overview of the approach and the current status of the joint project, which started at the beginning of 2023.

How to cite: Stenfert Kroese, J., Buchen-Tschiskale, C., Cordes, J., Dechow, R., Dittert, K., Dix, B., Fuchs, K., Gattinger, A., Greef, J.-M., Grosz, B., Hauschild, M., Mahboube, J., Kühne, J., Mielenz, H., Potthoff, T., Scheer, C., Schulz, F., Simpson, C., Wolf, B., and Well, R.: Mitigation measures of crop cultivation to reduce climate-impacting emissions from denitrification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10360, https://doi.org/10.5194/egusphere-egu24-10360, 2024.

X1.8
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EGU24-17865
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ECS
Thanawan Buacharoen, Yafei Guo, Eugenia Valsami - Jones, and Sami Ullah

The effect of nano fertilizers on Wheat vegetative characters

Thanawan Buacharoen1, Yafei Guo1, Eugenia Valsami-Jones1*, and Sami Ullah1

*Authors to whom correspondence should be addressed.

1School of Geography, Earth and Environmental Science, College of Life and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK

Wheat is the primary staple cereal in the world. It was the highest cultivation in 2018. According to the British Survey of Fertilizer Practice, total nitrogen use in Great Britain was reduced between 2021 and 2022. At the same time, the total phosphate did not change. Meanwhile, the usage of the total potash has increased compared to last year.  
Conventional fertilizer, which consists of nitrogen, phosphorous, and potassium nutrients, will release Greenhouse gas emissions. The other option to solve this problem is the nano fertilizer. Plants can easily absorb a tiny particle of nano fertilizer, reducing greenhouse gas emissions into the air. Therefore, this study focused on nano fertilizers' effect on plant growth. 

The first set of 30-day-old wheat plants was treated with amorphous calcium phosphate (nano - ACP), a potassium-bearing variant of the ACP (nano ACP - NPK) and a urea and potassium-bearing variant of the ACP (nano - UNPK). Moreover, three conventional fertilizers, which have the same nutrient quantity as same as nano fertilizers, were applied to the second set of plants to be a positive control. On the other hand, blank treatment was used to be a negative control. After harvesting the wheat plants, the shoot length and fresh weight were measured. Also, the ammonium concentration in the soil was examined with the colorimetric method. Maximum root weight was found in the wheat treated with nano–ACP (Average± SD. = 0.39±0.20). The nano ACP - NPK gave the highest value of shoot weight (Average ± SD. = 0.9 ± 0.10), number of seeds (84 seeds) and shoot length (Average ±SD.= 63.33 ± 4.29). However, the maximum ammonium concentration was found in the soil treated with nano ACP. All treatments' seed weight and shoot length differ at the P – value of less than 0.5. Our finding suggests that the nano fertilizers had enhanced vegetative characteristics compared with the conventional fertilizers.

Key word; amorphous calcium phosphate (nano - ACP), potassium-bearing variant of the ACP (nano ACP - NPK) and urea and potassium-bearing variant of the ACP (nano - UNPK)        

How to cite: Buacharoen, T., Guo, Y., Valsami - Jones, E., and Ullah, S.: The effect of nano fertilizers on wheat vegetative characters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17865, https://doi.org/10.5194/egusphere-egu24-17865, 2024.

X1.9
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EGU24-11614
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ECS
Rehab Almutairi

Title: Drought and eCO2 Effects on Oak Seedlings Growth, Soil Fertility, and Greenhouse Gases Fluxes

 

Authors: Rehab Al Mutairi, Nicholas Kettridge and Sami Ullah

 

Objective/Purpose:

This study explores the impact of water stress legacy and elevated CO2 on oak seedlings' growth, stomatal conductance, soil nutrient availability, and greenhouse gas (GHGs) fluxes. The research aims to unravel the intricate interplay of these factors under controlled glasshouse conditions.

 

Methods/Approach:

The experiment, conducted from mid-May to August 2023 at the University of Birmingham campus, involved oak seedlings grown under ambient CO2 and elevated CO2 chambers, subjected to two soil volumetric moisture levels (10% for drought, 30% for non-drought). Various parameters, including oak growth, stomatal conductance, soil nutrient availability, and GHGs flux, were measured and recorded throughout the three-month period. Additional analyses, including biomass, soil extracellular enzyme activities, microbial biomass of N and C, and net N mineralization, were conducted at the experiment's conclusion.

 

Key Findings/Results:

The study revealed compelling insights into the response of oak seedlings to drought stress and elevated CO2 conditions. Under drought scenarios, both under ambient and elevated CO2  environments, oak biomass and growth were notably diminished. Particularly, the roots exhibited a substantial increase in biomass, suggesting a coping strategy in search of water and nutrient resources of the seedlings. Stomatal conductance exhibited a decline under elevated carbon dioxide (eCO2), indicating a water-saving mechanism employed by plants. Additionally, extracellular enzyme activities were impacted by environmental conditions: a reduction was observed under drought stress. This reduction in enzyme functions aligns with a concurrent decrease in nutrient availability, highlighting a correlation between nutrient levels and enzyme activity reduction during drought conditions.

 

Conclusion/Implications:

The findings underscore the vulnerability of oak seedlings to drought stress, highlighting the importance of soil moisture management for their optimal growth. Additionally, the differential response between ambient and elevated CO2  levels emphasizes the need for nuanced considerations in future climate change scenarios. These insights contribute to our understanding of ecosystem responses to concurrent drought and elevated CO2 conditions.

 

Keywords:

Oak seedlings, Drought stress, Elevated CO2, Soil fertility, Greenhouse gas fluxes, Stomatal conductance, Biomass, Microbial biomass, Net N mineralization.

 

 

 

 

 

How to cite: Almutairi, R.: Drought and eCO2 Effects on Oak Seedlings Growth, Soil Fertility, and Greenhouse Gases Fluxes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11614, https://doi.org/10.5194/egusphere-egu24-11614, 2024.

X1.10
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EGU24-16927
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ECS
Adrian Simon Seeholzer, Anja Wunderlich, Ruben Steib, and Florian Einsiedl

Nitrate in groundwater can be converted microbially into N2. However, the lack of anoxic conditions (oxygen concentrations < 50 μmol/L) in the aquifer linked with the limitation of microbial available organic and inorganic electron donors may lead to insufficient denitrification in aquifers and nitrate concentration above the drinking water limit of 50 mg/L can be observed. In view of the increasing drinking-water scarcity associated with climate change and the continuing increase in nitrate concentrations in near-surface aquifers, it is urgently necessary and prudent to develop practicable and cost-effective methods to reduce nitrate to harmless N2.
Faced with the increasing nitrate pollution in groundwater, we want to develop a new cost-effective in-situ remediation technology by hydrogen/methane coupled denitrification. We hypothesize that the simultaneous injection of the two water soluble electron donors H2 and CH4 into groundwater may significantly enhance the rate of nitrate consumption by activation of denitrifying chemolithoautotrophic microorganisms that are already present in the groundwater.
Here we show the experimental set-up of the 2D-model aquifer (6 m x 1,8 m), the sampling strategy and show first results of the methane injection experiment. Measurements are performed along the flow direction and at several depths. Concentration profiles and stable isotope composition of methane (δ13C) and nitrate (δ15N) linked with oxygen concentrations shed light on the hydrogen-methane coupled denitrification potential in the model aquifer.

How to cite: Seeholzer, A. S., Wunderlich, A., Steib, R., and Einsiedl, F.: In-situ treatment of nitrate polluted groundwater by chemoautotrophic denitrification: flow-through tank experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16927, https://doi.org/10.5194/egusphere-egu24-16927, 2024.

X1.11
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EGU24-3699
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Highlight
Dianming Wu, Yaqi Song, Yuanchun Yu, and Peter Dörsch

The long-lived greenhouse gas nitrous oxide (N2O) and short-lived reactive nitrogen (Nr) gases such as ammonia (NH3), nitrous acid (HONO), and nitrogen oxides (NOx) are produced and emitted from fertilized soils and play a critical role for climate warming and air quality. However, only few studies have quantified the production and emission potentials for long- and short-lived gaseous nitrogen (N) species simultaneously in agricultural soils. To link the gaseous N species to intermediate N compounds [ammonium (NH4+), hydroxylamine (NH2OH), and nitrite (NO2)] and estimate their temperature change potential, ex-situ dry-out experiments were conducted with three Chinese agricultural soils. We found that HONO and NOx (NO + NO2) emissions mainly depend on NO2, while NH3 and N2O emissions are stimulated by NH4+ and NH2OH, respectively. Addition of 3,4-dimethylpyrazole phosphate (DMPP) and acetylene significantly reduced HONO and NOx emissions, while NH3 emissions were significantly enhanced in an alkaline Fluvo-aquic soil. These results suggest that ammonia-oxidizing bacteria (AOB) and complete ammonia-oxidizing bacteria (comammox Nitrospira) dominate HONO and NOx emissions in the alkaline Fluvo-aquic soil, while ammonia-oxidizing archaea (AOA) are the main source in the acidic Mollisol. DMPP effectively mitigated the warming effect in the Fluvo-aquic soil and the Ultisol. In conclusion, our findings highlight the important role of NO2 in stimulating HONO and NOx emissions from dryland agricultural soils. In addition, subtle differences of soil NH3, N2O, HONO, and NOx emissions indicated different N turnover processes, and should be considered in biogeochemical and atmospheric chemistry models.

How to cite: Wu, D., Song, Y., Yu, Y., and Dörsch, P.: Nitrite stimulates HONO and NOx but not N2O emissions in Chinese agricultural soils during nitrification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3699, https://doi.org/10.5194/egusphere-egu24-3699, 2024.

X1.12
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EGU24-15569
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Highlight
Steffen Schlüter, Maik Lucas, Balazs Grosz, Olaf Ippisch, Jan Zawallich, Hongxing He, Rene Dechow, David Kraus, Sergey Blagodatsky, Mehmet Senbeyram, Alexandra Kravchenko, Hans-Jörg Vogel, and Reinhard Well

Denitrification is a major component of the nitrogen cycle in soil that returns reactive nitrogen to the atmosphere. Denitrification activity is often concentrated spatially in anoxic microsites and temporally in ephemeral events, which presents a challenge for modelling. The anaerobic fraction of soil volume can be a useful predictor of denitrification in soils. Here, we provide a review of this soil characteristic, its controlling factors and its estimation from basic soil properties.

The concept of the anaerobic soil volume and its link to denitrification activity has undergone several paradigm shifts that came along with the advent of new oxygen and microstructure mapping techniques. The current understanding is that hotspots of denitrification activity are partially decoupled from air distances in the wet soil matrix and are mainly associated with particulate organic matter (POM) in the form of fresh plant residues or manure. POM fragments harbor large amounts of labile carbon that fuels local oxygen consumption and, as a result, these microsites differ in their aeration status from the surrounding soil matrix.

Current denitrification models link the anaerobic soil volume fraction to bulk oxygen concentration in different ways but take almost no account of microstructure information, such as the distance between POM and air-filled pores. Based on meta-analyses, we derive new empirical relationships to estimate conditions for the formation of anoxia at the microscale from basic soil properties and we outline how these empirical relationships could be used in the future to improve prediction accuracy of denitrification models at the soil profile scale.

How to cite: Schlüter, S., Lucas, M., Grosz, B., Ippisch, O., Zawallich, J., He, H., Dechow, R., Kraus, D., Blagodatsky, S., Senbeyram, M., Kravchenko, A., Vogel, H.-J., and Well, R.: The anaerobic soil volume as a controlling factor of denitrification , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15569, https://doi.org/10.5194/egusphere-egu24-15569, 2024.