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Nitrogen Cycling in the Anthropocene: Microbiological Processes, Land-atmosphere- Interactions and Global Change Feedbacks

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 N in terrestrial and aquatic ecosystems, and b) how reactive N enrichment of land and water will affect the future carbon sink of natural ecosystems as well as atmospheric exchanges of reactive (NH3, N2O, NOx, HONO) 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 cover microbe-mediated and physico-chemical transformations and transport of nitrogen across the land-water-air continuum in natural and managed ecosystems from local to regional and global scales. Furthermore, the session will explore interactions of N with other element cycles (e.g. those of phosphorus and carbon) and highlight the impacts for soil health, biodiversity and water and air quality. Latest developments in methodological and observational approaches for unravelling the complexities of N transformations and transport are of particular interest.

Convener: Sami Ullah | Co-conveners: Tuula Larmola, Dianming Wu, Lena RoheECSECS, Peter Dörsch
| Mon, 23 May, 15:10–18:30 (CEST)
Room 2.95

Mon, 23 May, 15:10–16:40

Chairpersons: Sami Ullah, Lena Rohe, Peter Dörsch

Introduction I

Feng Zhou and Xiaoqing Cui

Mitigating soil nitrous oxide (N2O) emissions is essential for staying below a 2°C warming threshold. However, accurate assessments of mitigation potential are limited by uncertainty and variability in direct emission factors (EFs). To assess where and why EFs differ, we create high-resolution maps of crop-specific EFs based on 1,507 georeferenced field observations. Here, using a data-driven approach, we show that EFs vary by two orders of magnitude over space. At global and regional scales, such variation is primarily driven by climatic and edaphic factors rather than the well-recognized management practices. Combining spatially explicit EFs with N surplus information, we conclude that global mitigation potential without compromising crop production is 30% [95% CI: 17-53%] of direct soil emissions of N2O, equivalent to the entire direct soil emissions of China and the United States combined. Two thirds (65%) of mitigation potential could be achieved on one fifth of global harvested area, mainly located in humid subtropical climate and across gleysols and acrisols. These findings highlight the value of a targeted policy approach on global hotspots that could deliver large N2O mitigation as well as environmental and food co-benefits.

How to cite: Zhou, F. and Cui, X.: Global hotspots of nitrous oxide mitigation potentials in croplands , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7612, https://doi.org/10.5194/egusphere-egu22-7612, 2022.

Junhui Yin et al.
Xin Huang et al.

Nitrate contamination in groundwater is affected by both anthropogenic activities and natural conditions, becoming one of the most prevalent problems worldwide. In this study, several machine learning methods including decision tree (DT), k nearest neighbors (KNN), logistic regression (LR), support vector machine (SVM), and extreme-gradient-boosted trees (Xgboost) were applied to predict the risk of groundwater nitrate contamination (NO3- > 50 mg L-1) in the riverside areas of lower reaches of Yangtze River, east China. The developed model included 13 hydrochemical parameters (K+, Na+, Ca2+, Mg2+, Cl-, SO42-, NH4+, NO2-, Fe, Mn, As, Sr, pH) and well depth as explanatory variables, and a total of 1089 groundwater samples. The results showed the hydrochemical dataset could effectively predict the risk of nitrate contamination, with a minimum accuracy of 82.7% in LR and maximal accuracy of 91.7% in SVM and Xgboost. However, only the Xgboost model under a cutoff probability of 0.3 had the best performance with the highest sensitivity of 80.3% and AUC 0.95, whereas other models had sensitivity lower than 60% with insufficient capability of identifying contaminated groundwater samples. The results showed that the ensemble learning method had a strong, robust prediction capability. In addition, the relative importance of K+, SO42-, and Cl- exceeded 0.65, indicating the dominant influence of domestic or industrial sewage in the study area due to widespread urbanization. Finally, we examined the relationship among nitrate contamination risk, land use type, the intensity of anthropogenic activities, and redox conditions and obtained the risk map of nitrate contamination in the study area. This study successfully proved the validity of predicting the risk of groundwater nitrate contamination using machine learning tools, which favors regional groundwater management and protection.

Keywords: groundwater; nitrate contamination; risk prediction; machine learning

How to cite: Huang, X., Jin, M., Liang, X., Su, J., and Ma, B.: Predicting the risk of groundwater nitrate contamination using machine learning tools, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1945, https://doi.org/10.5194/egusphere-egu22-1945, 2022.

Feiyang Chen et al.

Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) is a crucial link between carbon and nitrogen cycles in estuarine and coastal ecosystems. However, the factors that affect the heterogeneous variability in n-DAMO microbial abundance and activity across estuarine and intertidal wetlands remain unclear. This study examined the spatiotemporal variations in n-DAMO microbial abundance and associated activity in different estuarine and intertidal habitats via quantitative PCR and 13C stable isotope experiments. The results showed that Candidatus 'Methylomirabilis oxyfera' (M. oxyfera)-like DAMO bacteria and Candidatus 'Methanoperedens nitroreducens' (M. nitroreducens)-like DAMO archaea cooccurred in estuarine and intertidal wetlands, with a relatively higher abundance of the M. oxyfera-like bacterial pmoA gene (4.0×106-7.6×107 copies g-1 dry sediment) than the M. nitroreducens-like archaeal mcrA gene (4.5×105-9.4×107 copies g-1 dry sediment). The abundance of the M. oxyfera-like bacterial pmoA gene was closely associated with sediment pH and ammonium (P<0.05), while no significant relationship was detected between M. nitroreducens-like archaeal mcrA gene abundance and the measured environmental parameters (P>0.05). High n-DAMO microbial activity was observed, which varied between 0.2 and 84.3 nmol 13CO2 g-1 dry sediment day-1 for nitrite-DAMO bacteria and between 0.4 and 32.6 nmol 13CO2 g-1 dry sediment day-1 for nitrate-DAMO archaea. The total n-DAMO potential tended to be higher in the warm season and in the upstream freshwater and low-salinity estuarine habitats and was significantly related to sediment pH, total organic carbon, Fe(II), and Fe(III) contents (P<0.05). In addition to acting as an important methane (CH4) sink, n-DAMO microbes had the potential to consume a substantial amount of reactive N in estuarine and intertidal environments, with estimated nitrogen elimination rates of 0.5-224.7 nmol N g-1 dry sediment day-1. Overall, our investigation reveals the distribution pattern and controlling factors of n-DAMO bioprocesses in estuarine and intertidal marshes and gains a better understanding of the coupling mechanisms between carbon and nitrogen cycles.

How to cite: Chen, F., Zheng, Y., and Hou, L.: Microbial abundance and activity of nitrite/nitrate-dependent anaerobic methane oxidizers in estuarine and intertidal wetlands: Heterogeneity and driving factors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2143, https://doi.org/10.5194/egusphere-egu22-2143, 2022.

Tobias Stacke et al.
Lina Avila Clasen et al.
Peter Dörsch et al.

Enhancing carbon storage in managed soils through increased use of cover and catch crops in cereal cropping is at the heart of a carbon-negative agriculture. However, increased C storage by additional biomass production has a nitrogen cost, both in form of increased N fertilizer use and by potentially increasing nitrous oxide (N2O) emissions when cover crops decay. Frost-sensitive, N-rich aboveground biomass may be a particular problem during wintertime, as it may fuel off season N2O emissions during freezing-thawing cycles, which have been shown to dominate the annual N2O budget of many temperate and boreal sites. Here we report growing season and winter N2O emissions in a plot experiment in SE Norway, testing a barley production system with seven different catch and cover crops (perennial and Italian ryegrass, oilseed radish, summer and winter vetch, phacelia​ and an herb mixture) against a control without cover crops. Cover crops where either undersown in spring or established after harvesting barley. While ryegrass undersown to barley marginally reduced N2O emissions during the growing season, freeze-thaw cycles in winter resulted in significantly larger N2O emissions in treatments with N-rich cover crops (oilseed reddish, vetch) and Italian ryegrass. N2O budgets will be presented relative to aboveground yield and quality of cover crops and compared to potential souil organic carbon gains. 

How to cite: Dörsch, P., Sturite, I., and Trier Kjær, S.: High off-season nitrous oxide emissions negate potential soil C-gain from cover crops in boreal cereal cropping, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3066, https://doi.org/10.5194/egusphere-egu22-3066, 2022.

Isabel Zentgraf et al.

Most often, yield variability can be associated with differences in topography, soil properties and other environmental factors across agricultural landscapes. Ensuring high yield levels while simultaneously minimizing the risk of N-losses through inadequate use of fertilizers is especially difficult due to the high spatial variability of N transformations originating from those heterogeneities. Thus, understanding of N transformation in heterogeneous agricultural landscapes is key to an efficient and sustainable crop management.

To assess the impact of soil heterogeneity on N transformation processes, a novel field design was established in Tempelberg, North-East Germany. The experimental area was categorized in high yield and low yield potential zones based on historic yield and soil textural maps with field sizes of half a hectare. To display the small-scale soil heterogeneity within the patches, measurements were done along transects of gradients of yield potential.

We hypothesized that low yield soils with sandy texture, low soil water holding capacity (WHC) and locations at lower elevations within the field are associated with low N2O emissions and high N-leaching. In contrast, we expected high yield potential soils located at higher altitudes with a loamy texture to be characterized by high WHC, high N2O emissions and low N-leaching. Additionally, we postulated that edge effects across the transects may play a role due to patch design. We present results of the monthly N2O emission measurements done in fields cultivated with rape seed (Brassica napus L.), sunflower (Helianthus annuus L.) and maize (Zea mays L.), measured with NFT-NSS closed chambers, over a period of 6 months. 15N balances were calculated in the same fields tilled with sunflower (Helianthus annuus L.) and maize (Zea mays L.), by 15N tracer application and evaluation at three time points over growing season. Combination of N transformation processes and gaseous N fluxes in addition with WHC and topography allows for the identification of factors controlling soil N transformation and N availability in agricultural landscapes with high spatial variability of soil properties.

Soil dependent N2O measurements were observed across each transect. Elevation, texture as well as soil water content (SWC) showed a clear influence on N2O emissions. High emissions were measured in plots characterized by a loamy texture, high SWC and locations at higher elevations. In addition, lower emissions were measured at the edge point of the given transect, which could be described as an edge effect.

Evaluations of 15N tracer application results showed significant higher 15N leaching in low yield soils, which tend to have a higher sand content. High yield soils showed lower N-leaching. A strong dependence on soil texture and SWC was visible in the field cultivated with sunflower (Helianthus annuus L.): plots with higher sand content and lower SWC located at the center of the transect showed a higher N-leaching. This finding is in agreement with measured N2O emissions, which were noticeably lower in these areas.

In conclusion, soil heterogeneity in agricultural fields originating from differences in soil texture, SWC and topography show a clear impact on N transformations and N emissions.

How to cite: Zentgraf, I., Hoffmann, M., and Holz, M.: Does soil heterogeneity drive nitrogen transformation in agricultural landscapes? Towards an increased process understanding by quantification of N emissions and N transformation in soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3495, https://doi.org/10.5194/egusphere-egu22-3495, 2022.

Lena Rohe et al.

Even though the ability of fungi to produce the greenhouse gas nitrous oxide (N2O) during denitrification has been demonstrated, the proportion N2O emissions from fungal denitrification in soils cannot yet be determined or predicted. In order to develop methods for estimating the fungal proportion, N2O must be partitioned to bacterial and fungal denitrification. The denitrification regulatory phenotype (DRP) is well described for a number of bacterial strains (Bergaust et al. 2010, Bergaust et al. 2011), but to our knowledge there are only few data relating to the fungal DRP in terms of oxygen (O2) tension in fully stirred cultures at which they start producing N2O. The aim of this study was to analyse the kinetics of fungal denitrification combined with analysis of the isotopic composition of N2O. In particular, the 15N site preference of N2O (SP-N2O) is known to be a promising tool to differentiate between N2O produced during bacterial and fungal denitrification.

Four fungal species (Fusarium oxysporum, Fusarium decemcellulare, Fusarium solani fsp. pisi and Chaetomium funicola) were incubated as batch cultures in a robotized incubation system (Molstad et al. 2007) for 165h. Batch cultures were incubated in 120 ml flasks containing 50 ml of growth medium amended with ample amounts of carbon and nitrate in a He atmosphere with 2 vol%O2. To test for pH effects, a complex medium (Shoun et al. 1992) with pH values adjusted to 6.9 and 7.4 as well a minimal medium (Dox 1910) with a pH value of about 7.9 were used. O2 consumption and production of nitric oxide (NO), N2O, dinitrogen (N2) and carbon dioxide (CO2) were monitored at high temporal resolution while isotopic composition of N2O was analysed in samples taken manually at selected time points.

All four fungal cultures quickly consumed O2. NO production increased strongly before O2 was completely consumed and was followed by immediate N2O production. The kinetics of N2O production differed to published kinetics of denitrifying prokaryotes by showing a lower sensitivity to O2. This could result in a larger share of fungal denitrification under microaerobic conditions in soil.

Isotopic analysis of N2O confirmed previous results of specifically high SP-N2O values of fungal produced N2O. We further showed that SP-N2O values of fungal N2O are quite stable and do not depend on denitrification kinetics. Likewise, incubation conditions such as pH of the medium had little impact on SP-N2O values. These findings support the usage of SP-N2O values for partitioning N2O soil fluxes and provide a tool to study the biology of fungal denitrification under field conditions, which is needed to develop mitigation strategies of N2O from fungal denitrification.


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How to cite: Rohe, L., Well, R., Nadeem, S., and Dörsch, P.: Gas kinetics and stoichiometry from four fungi incubated under conditions favouring denitrification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5064, https://doi.org/10.5194/egusphere-egu22-5064, 2022.

General Discussion I

Mon, 23 May, 17:00–18:30

Chairpersons: Lena Rohe, Peter Dörsch, Sami Ullah

Nitrogen in the Anthropocene: Session II

Michael Dannenmann et al.

The paradigm that permafrost-affected soils show restricted mineral nitrogen (N) cycling in favor of organic N compounds is based on the observation that net N mineralization rates in these cold climates are negligible. However, we find here that this perception is wrong. By synthesizing published data on N cycling in the plant-soil-microbe system of permafrost ecosystems we show that gross ammonification and nitrification rates in active layers were of similar magnitude and showed a similar dependence on soil organic carbon (C) and total N concentrations as observed in temperate and tropical systems. Moreover, high protein depolymerization rates and only marginal effects of C:N stoichiometry on gross N turnover provided little evidence for N limitation. Instead, the rather short period when soils are not frozen is the single main factor limiting N turnover. High gross rates of mineral N cycling are thus facilitated by released protection of organic matter in active layers with nitrification gaining particular importance in N-rich soils, such as organic soils without vegetation. Our finding that permafrost-affected soils show vigorous N cycling activity is confirmed by the rich functional microbial community which can be found both in active and permafrost layers. The high rates of N cycling and soil N availability are supported by biological N fixation, while atmospheric N deposition in the Arctic still is marginal except for fire-affected areas. In line with high soil mineral N production, recent plant physiological research indicates a higher importance of mineral plant N nutrition than previously thought.

Our synthesis shows that mineral N production and turnover rates in active layers of permafrost-affected soils do not generally differ from those observed in temperate or tropical soils. We therefore suggest to adjust the permafrost N cycle paradigm, assigning a generally important role to mineral N cycling. This new paradigm suggests larger permafrost N climate feedbacks than assumed previously.

How to cite: Dannenmann, M., Ramm, E., Liu, C., Ambus, P., Butterbach-Bahl, K., Hu, B., Martikainen, P. J., Marushchak, M. E., Mueller, C. W., Rennenberg, H., Schloter, M., Siljanen, H. M. P., Voigt, C., Werner, C., and Biasi, C.: A review of the importance of mineral nitrogen cycling in the plant-soil-microbe system of permafrost-affected soils – changing the paradigm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11621, https://doi.org/10.5194/egusphere-egu22-11621, 2022.

Yu-Lin Yu et al.

Dissolved organic nitrogen (DON) is a kind of reactive nitrogen in the nitrogen cycling processes, which has been neglected for decades because of the difficulty in measurement, leading to underestimating the nitrogen saturation in the ecosystem. As a result, the need for a complete understanding of DON export behaviors is urgent. This study compares the DON export behaviors to previous studies, focusing on the relationship between DON, dissolved inorganic nitrogen (DIN), dissolved organic carbon (DOC), carbon-nitrogen coupling. We analyzed the data collected at the Fushan Experimental Forest (FEF) in northeastern Taiwan. Preliminary research results showed that (1) behaviors of DON export were unchanged between wet and dry seasons, but only switched at typhoon events, (2) the concentration of DOC was deficient in stream water, (3) unknown endmember between DON and DOC appeared at typhoon events, (4) the high bioavailability of DON occurred in soil and stream water, and (5) the concentration of DOC in soil pool was significantly higher than that of stream water. This study infers that typhoon disturbance appeared to alter the carbon limiting at FEF, causing the change of DON export patterns.

How to cite: Yu, Y.-L., Lee, L.-C., and Huang, J.-C.: Flow regime shifts the carbon-nitrogen coupling of dissolved organic nitrogen losses in a subtropical mountainous catchment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6942, https://doi.org/10.5194/egusphere-egu22-6942, 2022.

Ernesto Saiz et al.

The availability of nutrients is one of the main factors in soils that affect plant growth. This is something that has always been worrying humans; initially using natural fertilizers such as animal and human waste to enhance crop productivity. However, the industrial revolution brought the Haber-Bosch process (artificial nitrogen fixation), which posed a milestone on artificial fertilizers. The production of fertilizers increased exponentially during the twentieth century and is still increasing although at a slower pace. It has had not only positive results, e.g. food production, but is also causing major environmental, health and economic problems.

Because of these problems, it is critical to improve soil management strategies at the precise spatial scales in order to protect human health and the environment, while food production is also guaranteed. To do so, what is needed is a low-cost way to measure nutrients in the soil, in real-time, at different spatial scales.

During recent years, researchers have been working on the adaptation and modification of Ion Selective Electrodes for the analysis of nutrients directly in the soil. However, low precision and accuracy, intense instrument handling (pre and post-calibration), and complex data processing is preventing its general use.

We will present here two modifications of our first prototype of a low-cost ISE-based sensor probe. The probe allows measurements in situ and/or continuous monitoring of up to 16 chemical species. We will here showcase preliminary data obtained by measuring four replicates of four analytes. We also apply the Bayesian calibration methodology previously developed by us in order to improve the precision and accuracy of measurements.

How to cite: Saiz, E., Radu, A., Ullah, S., Del-Rio-Ruiz, R., Alsaedi, M., and Sonkusale, S.: Real-time soil nutrients monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8543, https://doi.org/10.5194/egusphere-egu22-8543, 2022.

Kathrin Rousk
Maureen Beaudor et al.

Ammonia (NH3) is a key species in the atmosphere, playing a crucial role in air quality and climate through the formation of sulfate and nitrate particles. Moreover, NH3 surface deposition alters ecosystems. About 85% of NH3 global anthropogenic emissions are related to food and feed production and in particular to the use of mineral fertilizers and manure management. Even though the estimate of the emissions from livestock can reach 36 Tg N/yr, they are generally not represented explicitly in global land surface models.  Most global chemistry transport models rely on bottom-up emission inventories subject to large uncertainties. Our objective consists of replacing these external emissions data by dynamical emissions computed by ORCHIDEE, a terrestrial ecosystem model including the carbon and the nitrogen cycles. This new version of the ORCHIDEE model includes a detailed integrated scheme for livestock management, from housing and storage to grazing emissions. Ultimately, our work aims at developing an interactive nitrogen cycle model in a coupled climate-chemistry-vegetation model in order to investigate the impact of NH3 emissions from livestock on atmospheric chemistry and climate, and the associated feedbacks.

In this study, we describe and present global NH3 emissions from livestock calculated based on the new version of the ORCHIDEE land surface model . We evaluate NH3 emissions simulated by ORCHIDEE with previous inventories and model estimates. An analysis of key parameters driving the soil NH3 emissions (pH of the manure, the timing of the N application, the surface atmospheric concentration etc… ) have also been performed in order to assess the sensitivity of the simulated emissions. Last, we investigate the impact of prescribing these new simulated emissions on atmospheric chemistry, using the global atmospheric chemistry transport model LMDZ-OR-INCA. The simulated NH3 atmospheric columns are evaluated by global and regional comparisons with the spaceborne IASI instrument measurements. The products used are monthly gridded NH3 distributions using morning observations of IASI-(Metop)A and IASI-(Metop)B for the period 2011-2017. In addition, we compare the ammonia atmospheric columns simulated based on the dynamical livestock emissions and based on reference bottom-up emission inventories. Finally, we investigate the impact of the different NH3 emission inventories on key atmospheric species concentrations.

How to cite: Beaudor, M., Vuichard, N., Lathière, J., Van Damme, M., Clarisse, L., and Hauglustaine, D.: Global NH3 emissions from livestock management : development of a module within a land surface model and impact on atmospheric chemistry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4806, https://doi.org/10.5194/egusphere-egu22-4806, 2022.

Shahar Baram et al.

In recent years, irrigation with nanobubbles aerated water (NB-water) [i.e., air or oxygen-NB (ONB)] has emerged as a new method to alleviate transient hypoxic conditions in the rhizosphere. We aimed to study the effect of surface and subsurface drip irrigation with ONB aerated waters [i.e., fresh (0.4 dS/m), secondary urban treated wastewater (TWW; 1.3 dS/m), saline (3dS/m)] on soil nitrogen transformations. Greenhouse lysimeter experiments were conducted in vertisol (58% clay), sand (98% sand), compost, and sand:compost (1:1) mixture, under well aerated and poorly aerated conditions. Ammonium-N to nitrate-N ratios in the irrigation waters ranged from 15% to 50%.  In all the experiments, irrigation with ONB water, with dissolved oxygen (DO) concentrations of 11 to 35 mg/L, increased the transient buildup of nitrite in the porewater, even under well-aerated conditions (soil air O2> 19%). The most significant effects were observed in the sand, sand:compost, and compost media, where nitrite concentrations were 2 – 8 times greater than the controls and reached over 65 mg/L. Despite the increased nitrite concentrations, irrigation with ONB waters reduced the nitrous oxide fluxes by 4 – 85%. Both phenomena suggested higher oxygen availability in the soil. Nitrite buildup implies that ammonia (NH3) oxidation may not be the rate-limiting step of nitrification under irrigation with ONB aerated water. 

How to cite: Baram, S., Weinstien, M., Kaplan, G., and Friedman, S.: The effects of drip irrigation with nanobubbles aerated water on soil N transformation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6937, https://doi.org/10.5194/egusphere-egu22-6937, 2022.

Rong Lang et al.

Fertilization in agriculture contributes substantially to an increase in nitrous oxide (N2O) emission to the atmosphere, optimizing fertilization is one of the mitigation strategies to reduce greenhouse gas (GHG) emissions while maintaining high crop production. In the Ultuna long-term frame trial, treatments including organic amendments and different types of mineral nitrogen fertilizers have been applied since1956 to quantify their effects on crop production, soil carbon and nitrogen cycling. However, the understanding of their effect on GHG emissions from soils is still quite limited. For this reason, we chose four treatments, including no fertilizer (control), calcium nitrate, ammonium sulfate and calcium cyanamide to study the mineral fertilizer type effect on N2O emissions and the plant-soil-microbe interactions over one crop growth period.  

N2O fluxes in the growing season were continuously measured from the 1 June to 15 Oct in 2019, using a Picarro N2O analyzer and 12 automated eosAC chambers. The frame trial has a randomized complete block design and we chose treatments in three blocks as replicates. In each plot, we placed two sensors to measure soil moisture and temperature. A mixed model was used to test the effect of fertilizer type and measurement date, with consideration of auto-correlations in the repeated measurements. Soil moisture and temperature were added to the regression model to quantify the controlling factors of the N2O fluxes. Measurement date was treated as a continuous variable.

The effects of both treatment and measurement date were statistically significant. Despite its higher pH values, the calcium nitrate  treatment emitted significantly more N2O than the control: 90.8±23.4 compared with 32.2±8.3 nmol m-2 s-1, respectively. The treatment with calcium cyanamide had pH-values and total N similar to those in the calcium nitrate treatment, but N2O emissions were 72% lower (25.0±6.5 nmol m-2 s-1) than the emission in the calcium nitrate treatment. Due to low soil pH, N2O fluxes were constantly low in the ammonium sulfate treatment, with an average emission of 24.3±6.3 nmol m-2 s-1. The temporal dynamics differed a lot between treatments, as suggested by significant interaction between treatment and measurement date. Further, regression with soil moisture and temperature showed that both variables contributed to explaining the temporal variation of N2O fluxes mainly in the control and calcium nitrate treatments. In contrast, N2O fluxes in the calcium cyanamide treatment were low throughout the growing season, suggesting that it effectively suppressed not only nitrification in the early growing season, but also the denitrification process in the late growing season.

Considering the highest maize biomass and lowest N2O emissions the calcium cyanamide treatment, using calcium cyanamide as nitrogen fertilizer has a great potential to reduce N2O emissions from agricultural soils without compromising crop production.  

How to cite: Lang, R., Shahbaz, M., Meurer, K. H. E., Börjesson, G., and Kätterer, T.: Fertilizer type effect on nitrous oxide (N2O) emissions in a Swedish long-term field experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7562, https://doi.org/10.5194/egusphere-egu22-7562, 2022.

Andrea Arangio et al.

Biological diversity and competition among species in ecosystems are sensitive to changes in macronutrient supply and nutrient availability. Human activity is intensively and extensively altering macronutrient cycles from a regional to a global scale with rates that can far exceed natural ones. Moreover, anthropogenic pollution exposes ecosystems to additional nutrients and stressors. These processes, although not well studied, can have a strong impact on ecosystem composition and productivity. In this study, we characterize the atmospheric deposition of bioavailable macronutrients from air pollution and study their impact on plant (oat) productivity and soil quality at a site in the Bois-Chamblard forest outside of Lausanne, Switzerland by Lake Geneva.

To evaluate the importance of atmospheric deposition as a nutrient path for soil and plants, we set up a mesocosm experiment where plants and bare soil were exposed to atmospheric deposition for four months (during Spring and Summer, 2021) and compared against replicates not exposed to atmospheric deposition. Carbon (C), N, P in plant and soil, as well as soil enzymatic activity, fungi and bacterial communities are quantified for each member of the mesocosm experiment. Quantification of the total nitrogen (N) and phosphorous (P), gas- and aerosol-species (inorganic/organic species and metals) in rain water, dry deposition and airborne particles and soil is carried out.

We find that plants exposed to atmospheric deposition display higher photosynthetic activity, larger N content and higher capacity to compete for nutrients in the soil. The soil community in the atmospheric deposition treatment shown higher nitrification rate and enzymatic activity towards lignin decomposition compared to the control. These results indicates that atmospheric pollutants act as plant fertilizers fostering their control on soil microbial community and accelerating soil nutrient stocks consumption.

How to cite: Arangio, A., Violaki, K., Quezada Rivera, J.-C., He, M., Motos, G., Bragazza, L., Grossiord, C., Buttler, A., and Nenes, A.: Atmospheric acidity and its impacts on macronutrient deposition and plant growth, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7977, https://doi.org/10.5194/egusphere-egu22-7977, 2022.

Caitlin Lewis et al.

Non-native coniferous plantations in the UK have long been associated with potentially negative impacts on surface water and groundwater quality due to high levels of nitrogen accumulation in their soils. Recent changes in UK forestry policy and targets and in attitudes towards biodiversity triggered a shift towards restocking conifer forests with broadleaved species. Broadleaved species are typically associated with lower rates of nitrogen deposition, scavenging and nitrate leaching, so it is often assumed that this change in management will enhance water quality. However, the conversion of coniferous woodland to broadleaved woodland typically stimulates the breakdown of organic matter, leading to a pulse release of nutrients which cannot be taken up rapidly enough by the nascent broadleaved forest.


To assess the significance of this process we conducted a study at Thetford Forest, Norfolk, a forest exposed to elevated levels of nitrogen deposition.  We measured throughfall and soil solution chemistry, soil C/N ratios, pH and net nitrification in a chronosequence of stands (0-72 years old) in the conversion process. Observed changes in organic soil C/N ratios indicate the potential for elevated nitrate leaching fluxes within the first decade post-conversion. Results also show an increase in net nitrification in the summer five to eight years post-conversion, followed by an accumulation of nitrogen in the deep mineral soils (30-90 cm depth) ten years post-conversion. Our ongoing analysis of deep soil solution and throughfall chemistry will confirm whether these observations are linked to elevated leaching fluxes in the first decade after conversion. Mature broadleaf stands were unexpectedly associated with greater concentrations of throughfall nitrate from August-October, and lower rates of soil nitrification in the summer than coniferous stands. Further analyses from winter-spring 2022 will explore seasonal variations in throughfall chemistry between broadleaf and coniferous stands in the context of elevated nitrogen deposition.


Our observations highlight the need to consider interactions between the effect of land management, seasonality and elevated deposition on nitrogen cycling processes to understand the impact of intensive nitrogen use on terrestrial nitrogen fluxes.    

How to cite: Lewis, C., Lukac, M., Vanguelova, E., and Ascott, M.: Risks of converting coniferous forests to broadleaved species, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11430, https://doi.org/10.5194/egusphere-egu22-11430, 2022.

Daniel Diaz-de-Quijano et al.

Anthropogenic disturbances of the nitrogen cycle are one of the most important issues for world ecology. Increased fluxes of atmospheric nitrogen deposition, including ammonium, nitrates, nitrites and other nitrogen oxides characterize the current state of nitrogen cycle. Scientists have found that this process might provide unproductive lakes with nitrogen enough for phytoplankton to turn from nitrogen to phosphorus limitation of growth. Nevertheless, atmospheric nitrogen deposition and its effect on phytoplankton primary production have not been uniformly studied around the world and significant areas remain understudied.

In this study, we measured the winter atmospheric deposition of nitrogen and phosphorus in the snow cover of an understudied region: the Ergaki Natural Park in the south of central Siberia. The concentrations in winter precipitation (40±16 mg of NO3-N m-2 0.58±0.13 mg of total P m-2) were used to estimate yearly yields (119±71 mg of NO3-N m-2 year-1 and 1.71±0.91 mg of total P m-2 year-1). These values approximately corresponded to the forecasts of worldwide mathematical models in the literature and were notably low for terrestrial sites, especially in the case of phosphorus. Measurements of d15N, total N and P in lake sediment cores confirmed the minor role of eventual atmospheric N deposition in the studied lakes, as compared to terrestrial inputs.

The atmospheric nitrogen deposition on the Ergaki mountain ridge was slightly lower than in northern Sweden, where the low atmospheric nitrogen deposition had been found to trigger nitrogen (instead of phosphorus) limitation of phytoplankton growth in unproductive lakes. Nevertheless, atmospheric phosphorus deposition in the study site was among the lowest ones on the mainland, if not the lowest. Due to this extremely low content of atmospheric nutrient deposition, the stoichiometry of N:P in snow and lake water did not correlate, so our lakes did not belong to the group of lakes in the world that are influenced by atmospheric deposition of nutrients. According to our observations, both nitrogen and phosphorus can periodically be limiting factors of phytoplankton in Ergaki lakes.

In conclusion, firstly, the Ergaki Natural Park is an ideal place to study the effects of global warming with a minimal interference of atmospheric nitrogen deposition. Secondly, even at low levels of atmospheric nitrogen deposition in places where atmospheric phosphorus deposition is very low, nitrogen is not necessarily the limiting factor of phytoplankton growth, which may contradict the general character of the currently accepted paradigm. Further studies should check the year-round deposition of nutrients and expand the number of lakes and regions in Siberia, where a significant part of the lakes is not subject to severe anthropogenic pollution.

This study was funded by the Russian Foundation of Basic Research grant number 20-04-00960.

How to cite: Diaz-de-Quijano, D., Ageev, A. V., Moshkin, N. V., Ivanova, E. A., Anishchenko, Y. D., Anishchenko, O. V., and Sushchik, N. N.: Low atmospheric nitrogen deposition in southern central Siberia does not trigger any nitrogen limitation in the growth of mountain lake phytoplankton, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13309, https://doi.org/10.5194/egusphere-egu22-13309, 2022.

Fotis Sgouridis et al.

The current climate trajectory in conjunction with agricultural intensification and the reliance on synthetic fertilisers, present further threat to the resilience of future food production through their contributions to soil degradation and consequent climatic feedback. Innovative sustainable agricultural technologies are needed to produce nutritious and equitable food products in line with the UN’s goal for Zero Hunger and sustainable development. Glacial Rock Flour (GRF) is a fine mineral rock dust, made available through the glacial abrasion of bedrock, and is often enriched in nutrients (e.g. Potassium, Phosphorous, Silicon, trace elements) but low in Nitrogen. It would therefore be a suitable soil fertility amendment for legume crops grown in acidic, nutrient poor soils often found in many mountainous regions (e.g. Hindu Kush Himalaya), where GRF is considered an alluvial ‘waste’ silting up dams and reservoirs. We have investigated the effect of GRF soil amendments in soil-plant mesocosms using a typical UK silt loam arable soil (pH~7) for cultivating red clover (Trifolium pratense) inoculated with Rhizobium. GRF from the Chhota Shigri (India) and Sólheimajökull (Iceland) glaciers were applied at 2 and 20 T/ha, while no GRF treatments included synthetic fertilizer applications of phosphorus (P), potassium (K) and P+K, and they were all compared against control red clover plants grown with no soil amendments. The nitrogen fixation capacity of red clover was estimated via 15N natural abundance against a rye grass control (Lolium perenne) in two harvests on weeks 14 and 19. Both 20 T/ha GRF treatments appeared to stimulate fixed nitrogen yield compared to synthetic fertilizer treatments and control red clover plants, while the stimulation was more pronounced in the 2nd harvest as the soil nutrients were progressively depleted. Soil greenhouse gas fluxes over the growth period (weeks 4-14) were monitored by enclosing pots in sealed chambers. While no difference was observed in carbon dioxide fluxes between treatments, nitrous oxide (N2O) flux was negative for all red clover mesocosms with the N2O reduction being more prominent in both 20 T/ha GRF treatments towards the end of the first growth period (week 14). Gross N mineralization and nitrification were estimated in post-harvest soils from all the mesocosms using the isotope dilution method, while 15N-N2O and 15N-N2 production were also measured after amending the soils with 98 at% 15N-NH4+ and 15N-NO3-.  Gross N mineralization was not different between treatments, while nitrification was non-detectable, indicating a very tightly coupled N cycle between Rhizobium and red clover. However, when excess nitrate was applied, bacterial denitrification was active but the amendment of the soils with GRF appeared to reduce the production of N2O and promote complete denitrification to N2. Our novel study on the properties and application of GRF as a sustainable soil fertility amendment under a low nitrogen cropping system, holds promise that it can promote leguminous nitrogen fixation and a tightly-coupled N cycle that maximises N-use efficiency while mitigating N2O emissions by promoting complete denitrification.

How to cite: Sgouridis, F., Forrester, H., Tingey, S., and Wadham, J.: Glacial Rock Flour as soil fertility amendment increases N fixation activity in red clover and enhances soil N2O reduction., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5489, https://doi.org/10.5194/egusphere-egu22-5489, 2022.

General Discussion II