scholarly journals The isotopic composition of atmospheric nitrous oxide observed at the high-altitude research station Jungfraujoch, Switzerland

2020 ◽  
Vol 20 (11) ◽  
pp. 6495-6519 ◽  
Author(s):  
Longfei Yu ◽  
Eliza Harris ◽  
Stephan Henne ◽  
Sarah Eggleston ◽  
Martin Steinbacher ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Isotopic Composition ◽  
High Altitude ◽  
High Precision ◽  
Large Scale ◽  
Late Summer ◽  
Site Preference ◽  
Research Station ◽  
N2o Production ◽  
Mixing Ratios

Abstract. Atmospheric nitrous oxide (N2O) levels have been continuously growing since preindustrial times. Mitigation requires information about sources and sinks on the regional and global scales. Isotopic composition of N2O in the atmosphere could contribute valuable constraints. However, isotopic records of N2O in the unpolluted atmosphere remain too scarce for large-scale N2O models. Here, we report the results of discrete air samples collected weekly to biweekly over a 5-year period at the high-altitude research station Jungfraujoch, located in central Switzerland. High-precision N2O isotopic measurements were made using a recently developed preconcentration and laser spectroscopy technique. The measurements of discrete samples were accompanied by in situ continuous measurements of N2O mixing ratios. Our results indicate a pronounced seasonal pattern with minimum N2O mixing ratios in late summer, associated with a maximum in δ15Nbulk and a minimum in intramolecular 15N site preference (δ15NSP). This pattern is most likely due to stratosphere–troposphere exchange (STE), which delivers N2O-depleted but 15N-enriched air from the stratosphere into the troposphere. Variability in δ15NSP induced by changes in STE may be masked by biogeochemical N2O production processes in late summer, which are possibly dominated by a low-δ15NSP pathway of N2O production (denitrification), providing an explanation for the observed seasonality of δ15NSP. Footprint analyses and atmospheric transport simulations of N2O for Jungfraujoch suggest that regional emissions from the planetary boundary layer contribute to seasonal variations of atmospheric N2O isotopic composition at Jungfraujoch, albeit more clearly for δ15NSP and δ18O than for δ15Nbulk. With the time series of 5 years, we obtained a significant interannual trend for δ15Nbulk after deseasonalization (-0.052±0.012 ‰ a−1), indicating that the atmospheric N2O increase is due to isotopically depleted N2O sources. We estimated the average isotopic signature of anthropogenic N2O sources with a two-box model to be -8.6±0.6 ‰ for δ15Nbulk, 34.8±3 ‰ for δ18O and 10.7±4 ‰ for δ15NSP. Our study demonstrates that seasonal variation of N2O isotopic composition in the background atmosphere is important when determining interannual trends. More frequent, high-precision and interlaboratory-compatible measurements of atmospheric N2O isotopocules, especially for δ15NSP, are needed to better constrain anthropogenic N2O sources and thus the contribution of biogeochemical processes to N2O growth on the global scale.

scholarly journals The isotopic composition of atmospheric nitrous oxide observed at the high-altitude research station Jungfraujoch, Switzerland

2019 ◽  
Author(s):  
Longfei Yu ◽  
Eliza Harris ◽  
Stephan Henne ◽  
Sarah Eggleston ◽  
Martin Steinbacher ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Isotopic Composition ◽  
High Altitude ◽  
High Precision ◽  
Large Scale ◽  
Late Summer ◽  
Site Preference ◽  
Research Station ◽  
N2o Production ◽  
Mixing Ratios

Abstract. Atmospheric nitrous oxide (N2O) levels have been continuously growing since preindustrial times. Mitigation requires information about sources and sinks on the regional and global scales. Isotopic composition of N2O in the atmosphere could contribute valuable constraints. However, isotopic records of N2O in the unpolluted atmosphere remain too scarce for large-scale N2O models. Here, we report the results of discrete air samples collected weekly to bi-weekly over a five-year period at the high-altitude research station Jungfraujoch, located in central Switzerland. High-precision N2O isotopic measurements were made using a recently developed preconcentration-laser spectroscopy technique. The measurements of discrete samples were accompanied by in situ continuous measurements of N2O mixing ratios. Our results indicate a pronounced seasonal pattern with minimum N2O mixing ratios in late summer, associated with a maximum in δ15Nbulk and a minimum in intramolecular 15N site preference (δ15NSP). This pattern is most likely due to stratosphere-troposphere exchange (STE), which delivers N2O-depleted but 15N-enriched air from the stratosphere into the troposphere. Variability in δ15NSP induced by changes in STE may be masked by biogeochemical N2O production processes in late summer, which are possibly dominated by a low-δ15NSP pathway of N2O production (denitrification), providing an explanation for the observed seasonality of δ15NSP. Footprint analyses and atmospheric transport simulations of N2O for Jungfraujoch suggest that regional emissions from the planetary boundary layer contribute to seasonal variations of atmospheric N2O isotopic composition at Jungfraujoch, albeit more clearly for δ15NSP and δ18O than for δ15Nbulk. With the time-series of five years, we obtained a significant interannual trend for δ15Nbulk after deseasonalization (−0.052±0.012 ‰ a−1), indicating that the atmospheric N2O increase is due to isotopically depleted N2O sources. We estimated the average isotopic signature of anthropogenic N2O sources with a two-box model to be −8.6±0.6 ‰ for δ15Nbulk, 34.8±3 ‰ for δ18O and 10.7±4 ‰ for δ15NSP. Our study demonstrates that seasonal variation of N2O isotopic composition in the background atmosphere is important when determining interannual trends. More frequent, high-precision and inter-laboratory compatible measurements of atmospheric N2O isotopocules, especially for δ15NSP, are needed to better constrain anthropogenic N2O sources, and thus the contribution of biogeochemical processes to N2O growth on the global scale.

scholarly journals Soil Denitrifier Community Size Changes with Land Use Change to Perennial Bioenergy Cropping Systems

2016 ◽  
Author(s):  
Karen A. Thompson ◽  
Bill Deen ◽  
Kari E. Dunfield
Keyword(s):  
Land Use ◽  
16S Rrna ◽  
Land Use Change ◽  
Crop Production ◽  
Large Scale ◽  
Perennial Grasses ◽  
N2o Emissions ◽  
Research Station ◽  
N2o Production ◽  
Nirs Gene

Abstract. Dedicated biomass crops are required for future bioenergy production. However, the effects of large-scale land use change (LUC) from traditional annual crops, such as corn-soybean rotations to the perennial grasses (PGs) switchgrass and miscanthus on soil microbial community functioning is largely unknown. Specifically, ecologically significant denitrifying communities, which regulate N2O production and consumption in soils, may respond differently to LUC due to differences in carbon (C) and nitrogen (N) inputs between crop types and management systems. Our objective was to quantify bacterial denitrifying gene abundances as influenced by corn-soybean crop production compared to PG biomass production. A field trial was established in 2008 at the Elora Research Station in Ontario, Canada (n = 30), with miscanthus and switchgrass grown alongside corn-soybean rotations at different N rates (0 and 160 kg N ha-1) and biomass harvest dates within PG plots. Soil was collected on four dates from 2011–2012 and quantitative PCR was used to enumerate the total bacterial community (16S rRNA), and communities of bacterial denitrifiers by targeting nitrite reductase (nirS) and N2O reductase (nosZ) genes. Miscanthus produced significantly larger yields and supported larger nosZ denitrifying communities than corn-soybean rotations regardless of management, indicating large-scale LUC from corn-soybean to miscanthus may be suitable in variable Ontario conditions while potentially mitigating soil N2O emissions. Harvesting switchgrass in the spring decreased yields in N-fertilized plots, but did not affect gene abundances. Standing miscanthus overwinter resulted in higher 16S rRNA and nirS gene copies than in fall-harvested crops. However, the size of the total (16S rRA) and denitrifying communities changed differently over time and in response to LUC, indicating varying controls on these communities.

scholarly journals Biogeochemical controls and isotopic signatures of nitrous oxide production by a marine ammonia-oxidizing bacterium

2010 ◽  
Vol 7 (9) ◽  
pp. 2695-2709 ◽  
Author(s):  
C. H. Frame ◽  
K. L. Casciotti
Keyword(s):  
Nitrous Oxide ◽  
Stratospheric Ozone ◽  
Nitrifying Bacteria ◽  
Site Preference ◽  
Ammonia Oxidizing Bacteria ◽  
N2o Production ◽  
O2 Concentration ◽  
Cell Densities ◽  
Dissolved O2

Abstract. Nitrous oxide (N2O) is a trace gas that contributes to the greenhouse effect and stratospheric ozone depletion. The N2O yield from nitrification (moles N2O-N produced per mole ammonium-N consumed) has been used to estimate marine N2O production rates from measured nitrification rates and global estimates of oceanic export production. However, the N2O yield from nitrification is not constant. Previous culture-based measurements indicate that N2O yield increases as oxygen (O2) concentration decreases and as nitrite (NO2−) concentration increases. Here, we have measured yields of N2O from cultures of the marine β-proteobacterium Nitrosomonas marina C-113a as they grew on low-ammonium (50 μM) media. These yields, which were typically between 4 × 10−4 and 7 × 10−4 for cultures with cell densities between 2 × 102 and 2.1 × 104 cells ml−1, were lower than previous reports for ammonia-oxidizing bacteria. The observed impact of O2 concentration on yield was also smaller than previously reported under all conditions except at high starting cell densities (1.5 × 106 cells ml−1), where 160-fold higher yields were observed at 0.5% O2 (5.1 μM dissolved O2) compared with 20% O2 (203 μM dissolved O2). At lower cell densities (2 × 102 and 2.1 × 104 cells ml−1), cultures grown under 0.5% O2 had yields that were only 1.25- to 1.73-fold higher than cultures grown under 20% O2. Thus, previously reported many-fold increases in N2O yield with dropping O2 could be reproduced only at cell densities that far exceeded those of ammonia oxidizers in the ocean. The presence of excess NO2− (up to 1 mM) in the growth medium also increased N2O yields by an average of 70% to 87% depending on O2 concentration. We made stable isotopic measurements on N2O from these cultures to identify the biochemical mechanisms behind variations in N2O yield. Based on measurements of δ15Nbulk, site preference (SP = δ15Nα−δ15Nβ), and δ18O of N2O (δ18O-N2O), we estimate that nitrifier-denitrification produced between 11% and 26% of N2O from cultures grown under 20% O2 and 43% to 87% under 0.5% O2. We also demonstrate that a positive correlation between SP and δ18O-N2O is expected when nitrifying bacteria produce N2O. A positive relationship between SP and δ18O-N2O has been observed in environmental N2O datasets, but until now, explanations for the observation invoked only denitrification. Such interpretations may overestimate the role of heterotrophic denitrification and underestimate the role of ammonia oxidation in environmental N2O production.

scholarly journals Nitrous oxide distribution and its origin in the central and eastern South Pacific Subtropical Gyre

2007 ◽  
Vol 4 (5) ◽  
pp. 729-741 ◽  
Author(s):  
J. Charpentier ◽  
L. Farias ◽  
N. Yoshida ◽  
N. Boontanon ◽  
P. Raimbault
Keyword(s):  
Nitrous Oxide ◽  
Coastal Upwelling ◽  
South Pacific ◽  
Site Preference ◽  
Natural Environments ◽  
Intermediate Water ◽  
N2o Production ◽  
South Pacific Ocean ◽  
Nitrifier Denitrification ◽  
Organic Particles

Abstract. The mechanisms of microbial nitrous oxide (N2O) production in the ocean have been the subject of many discussions in recent years. New isotopomeric tools can further refine our knowledge of N2O sources in natural environments. This study compares hydrographic, N2O concentration, and N2O isotopic and isotopomeric data from three stations along a coast-perpendicular transect in the South Pacific Ocean, extending from the center (Sts. GYR and EGY) of the subtropical oligotrophic gyre (~26° S; 114° W) to the upwelling zone (St. UPX) off the central Chilean coast (~34° S). Although AOU/N2O and NO3− trends support the idea that most of the N2O (mainly from intermediate water (200–600 m)) comes from nitrification, N2O isotopomeric composition (intramolecular distribution of 15N isotopes) expressed as SP (site preference of 15N) shows low values (10 to 12\\permil) that could be attributed to the production through of microbial nitrifier denitrification (reduction of nitrite to N2O mediated by ammonium oxidizers). The coincidence of this SP signal with high – stability layer, where sinking organic particles can accumulate, suggests that N2O could be produced by nitrifier denitrification inside particles. It is postulated that deceleration of particles in the pycnocline can modify the advection - diffusion balance inside particles, allowing the accumulation of nitrite and O2 depletion suitable for nitrifier denitrication. As lateral advection seems to be relatively insignificant in the gyre, in situ nitrifier denitrification could account for 40–50% of the N2O produced in this layer. In contrast, coastal upwelling system is characterized by O2 deficient condition and some N deficit in a eutrophic system. Here, N2O accumulates up to 480% saturation, and isotopic and isotopomer signals show highly complex N2O production processes, which presumably reflect both the effect of nitrification and denitrification at low O2 levels on N2O production, but net N2O consumption by denitrification was not observed.

scholarly journals High-precision dual-inlet IRMS measurements of the stable isotopes of CO<sub>2</sub> and the N<sub>2</sub>O / CO<sub>2</sub> ratio from polar ice core samples

2014 ◽  
Vol 7 (11) ◽  
pp. 3825-3837 ◽  
Author(s):  
T. K. Bauska ◽  
E. J. Brook ◽  
A. C. Mix ◽  
A. Ross
Keyword(s):  
Isotopic Composition ◽  
High Precision ◽  
Water Vapor Pressure ◽  
Ice Core ◽  
Ice Cores ◽  
Mass Spectrometric Method ◽  
Polar Ice ◽  
Mixing Ratios ◽  
Core Samples ◽  
Oxygen Isotopic

Abstract. An important constraint on mechanisms of past carbon cycle variability is provided by the stable isotopic composition of carbon in atmospheric carbon dioxide (δ13C-CO2) trapped in polar ice cores, but obtaining very precise measurements has proven to be a significant analytical challenge. Here we describe a new technique to determine the δ13C of CO2 at very high precision, as well as measuring the CO2 and N2O mixing ratios. In this method, ancient air is extracted from relatively large ice samples (~400 g) with a dry-extraction "ice grater" device. The liberated air is cryogenically purified to a CO2 and N2O mixture and analyzed with a microvolume-equipped dual-inlet IRMS (Thermo MAT 253). The reproducibility of the method, based on replicate analysis of ice core samples, is 0.02‰ for δ13C-CO2 and 2 ppm and 4 ppb for the CO2 and N2O mixing ratios, respectively (1σ pooled standard deviation). Our experiments show that minimizing water vapor pressure in the extraction vessel by housing the grating apparatus in a ultralow-temperature freezer (−60 °C) improves the precision and decreases the experimental blank of the method to −0.07 ± 0.04‰. We describe techniques for accurate calibration of small samples and the application of a mass-spectrometric method based on source fragmentation for reconstructing the N2O history of the atmosphere. The oxygen isotopic composition of CO2 is also investigated, confirming previous observations of oxygen exchange between gaseous CO2 and solid H2O within the ice archive. These data offer a possible constraint on oxygen isotopic fractionation during H2O and CO2 exchange below the H2O bulk melting temperature.

scholarly journals Isotopomeric characterization of nitrous oxide produced by reaction of enzymes extracted from nitrifying and denitrifying bacteria

2014 ◽  
Vol 11 (10) ◽  
pp. 2679-2689 ◽  
Author(s):  
T. Yamazaki ◽  
T. Hozuki ◽  
K. Arai ◽  
S. Toyoda ◽  
K. Koba ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Pure Culture ◽  
Paracoccus Denitrificans ◽  
In Vivo Studies ◽  
Site Preference ◽  
Ammonia Oxidizing Bacteria ◽  
Small Contribution ◽  
N2o Production ◽  
No2 Reduction

Abstract. Nitrous oxide (N2O) is a potent greenhouse gas and produced in denitrification and nitrification by various microorganisms. Site preference (SP) of 15N in N2O, which is defined as the difference in the natural abundance of isotopomers 14N15NO and 15N14NO relative to 14N14NO, has been reported to be a useful tool to quantitatively distinguish N2O production pathways. To determine representative SP values for each microbial process, we firstly measured SP of N2O produced in the enzyme reaction of hydroxylamine oxidoreductase (HAO) purified from two species of ammonia oxidizing bacteria (AOB), Nitrosomonas europaea and Nitrosococcus oceani, and that of nitric oxide reductase (NOR) from Paracoccus denitrificans. The SP value for NOR reaction (−5.9 ± 2.1‰) showed nearly the same value as that reported for N2O produced by P. denitrificans in pure culture. In contrast, SP value for HAO reaction (36.3 ± 2.3‰) was a little higher than the values reported for N2O produced by AOB in aerobic pure culture. Using the SP values obtained by HAO and NOR reactions, we calculated relative contribution of the nitrite (NO2–) reduction (which is followed by NO reduction) to N2O production by N. oceani incubated under different O2 availability. Our calculations revealed that previous in vivo studies might have underestimated the SP value for the NH2OH oxidation pathway possibly due to a small contribution of NO2– reduction pathway. Further evaluation of isotopomer signatures of N2O using common enzymes of other processes related to N2O would improve the isotopomer analysis of N2O in various environments.

scholarly journals Soil denitrifier community size changes with land use change to perennial bioenergy cropping systems

SOIL ◽  
2016 ◽  
Vol 2 (4) ◽  
pp. 523-535 ◽  
Author(s):  
Karen A. Thompson ◽  
Bill Deen ◽  
Kari E. Dunfield
Keyword(s):  
Land Use ◽  
16S Rrna ◽  
Land Use Change ◽  
Crop Production ◽  
Large Scale ◽  
Perennial Grasses ◽  
N2o Emissions ◽  
Research Station ◽  
N2o Production ◽  
Nirs Gene

Abstract. Dedicated biomass crops are required for future bioenergy production. However, the effects of large-scale land use change (LUC) from traditional annual crops, such as corn–soybean rotations to the perennial grasses (PGs) switchgrass and miscanthus, on soil microbial community functioning is largely unknown. Specifically, ecologically significant denitrifying communities, which regulate N2O production and consumption in soils, may respond differently to LUC due to differences in carbon (C) and nitrogen (N) inputs between crop types and management systems. Our objective was to quantify bacterial denitrifying gene abundances as influenced by corn–soybean crop production compared to PG biomass production. A field trial was established in 2008 at the Elora Research Station in Ontario, Canada (n  =  30), with miscanthus and switchgrass grown alongside corn–soybean rotations at different N rates (0 and 160 kg N ha−1) and biomass harvest dates within PG plots. Soil was collected on four dates from 2011 to 2012 and quantitative PCR was used to enumerate the total bacterial community (16S rRNA) and communities of bacterial denitrifiers by targeting nitrite reductase (nirS) and N2O reductase (nosZ) genes. Miscanthus produced significantly larger yields and supported larger nosZ denitrifying communities than corn–soybean rotations regardless of management, indicating large-scale LUC from corn–soybean to miscanthus may be suitable in variable Ontario climatic conditions and under varied management, while potentially mitigating soil N2O emissions. Harvesting switchgrass in the spring decreased yields in N-fertilized plots, but did not affect gene abundances. Standing miscanthus overwinter resulted in higher 16S rRNA and nirS gene copies than in fall-harvested crops. However, the size of the total (16S rRNA) and denitrifying bacterial communities changed differently over time and in response to LUC, indicating varying controls on these communities.

scholarly journals Isotopomeric characterization of nitrous oxide produced by reaction of enzymes extracted from nitrifying and denitrifying bacteria

2013 ◽  
Vol 10 (10) ◽  
pp. 16615-16643 ◽  
Author(s):  
T. Yamazaki ◽  
T. Hozuki ◽  
K. Arai ◽  
S. Toyoda ◽  
K. Koba ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Pure Culture ◽  
Paracoccus Denitrificans ◽  
In Vivo Studies ◽  
Site Preference ◽  
Ammonia Oxidizing Bacteria ◽  
Small Contribution ◽  
N2o Production ◽  
No2 Reduction

Abstract. Nitrous oxide (N2O) is a potent greenhouse gas and produced in denitrification and nitrification in environmental nitrogen cycle by various microorganism. Site preference (SP) of 15N in N2O, which is defined as the difference in the natural abundance of isotopomers 14N15NO and 15N14NO relative to 14N14NO, has been reported to be a useful tool to quantitatively distinguish N2O production pathway. To determine representative SP value for each microbial process, we firstly measured SP of N2O produced in the enzyme reaction of hydroxylamine oxidoreductase (HAO) purified from two species of ammonia oxidizing bacteria (AOB), Nitrosomonas europaea and Nitrosococcus oceani, and that of nitric oxide reductase (NOR) from Paracoccus denitrificans, respectively. The SP value for NOR reaction (−5.9 ± 2.1‰) showed nearly the same value as that reported for N2O produced by P. denitrificans in pure culture. In contrast, SP value for HAO reaction (36.3 ± 2.3‰) was a little higher than the values reported for N2O produced by AOB in aerobic pure culture. Using the SP values obtained by HAO and NOR reactions, we calculated relative contribution of the nitrite (NO2–) reduction (which is followed by NO reduction) to N2O production by N. oceani incubated under different O2 availability. Our calculations revealed that previous in vivo studies might have underestimated the SP value for NH2OH oxidation pathway possibly due to a small contribution of NO2– reduction pathway. Further evaluation of isotopomer signatures of N2O using common enzymes of other processes related to N2O would improve the isotopomer analysis of N2O in various environments.

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