This title appears in the Scientific Report :
2014
Mechanisms of inorganic nitrous oxide production in soils during nitrification and their dependence on soil properties
Mechanisms of inorganic nitrous oxide production in soils during nitrification and their dependence on soil properties
N2O is an important greenhouse gas and today’s single most ozone depleting substance. Soils have been identified as the major source of N2O. Microbial processes nitrification and denitrification are considered the major N2O sources. However, N2O production in soils, especially during nitrification,...
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Personal Name(s): | Heil, Jannis (Corresponding Author) |
---|---|
Liu, Shurong / Vereecken, Harry / Brüggemann, Nicolas | |
Contributing Institute: |
Agrosphäre; IBG-3 |
Published in: |
The nitrogen challenge: Building a blueprint for nitrogen use efficiency and food security |
Imprint: |
2014
|
Physical Description: |
437-438 |
ISBN: |
978-972-8669-56-0 |
Conference: | 18th Nitrogen Workshop, Lisbon (Portugal), 2014-06-30 - 2014-07-03 |
Document Type: |
Contribution to a book Contribution to a conference proceedings |
Research Program: |
Terrestrial Systems: From Observation to Prediction Modelling and Monitoring Terrestrial Systems: Methods and Technologies |
Publikationsportal JuSER |
N2O is an important greenhouse gas and today’s single most ozone depleting substance. Soils have been identified as the major source of N2O. Microbial processes nitrification and denitrification are considered the major N2O sources. However, N2O production in soils, especially during nitrification, is far from being completely understood. N2O release during both processes has been described by Firestone and Davidson (1989) in their conceptual ‘hole-in-the-pipe’ model. The model attributes N2O emissions from soils during nitrification and denitrification to leaks in the N transformation from ammonium to nitrate and the incomplete stepwise reduction of nitrate to N2. Until now, the mechanisms behind this ‘leaky’ N2O emission during nitrification have not been explained so it is unknown what drives these emissions. Several abiotic reactions involving nitrification intermediate hydroxylamine (NH2OH) have been identified leading to N2O emissions, but are neglected in most current studies. It is known that NH2OH can be oxidized by several soil constituents to form N2O (Bremner 1997). For better mitigation strategies it is mandatory to understand the underlying processes of N2O production during nitrification and their controlling factors.We studied N2O emissions from different soils in laboratory incubations. Soils used covered a wide range of land use types from cropland to grassland and forest. Soil incubations were conducted at conditions favorable for nitrification. Soil samples were placed into vials, deionized water or NH2OH solution was added, respectively, and water content was adjusted to the desired level. Vials were closed immediately for incubation. Experiments were conducted with non-sterile and sterile (autoclaved) soils. After 6 hours of incubation time the vials were sampled for N2O mixing ratios. Additionally, CO2 mixing ratios were analyzed to quantify microbial activity. For quantification of both gases a gas chromatograph (PerkinElmer, USA) was used. To get insight into the dynamics of N2O formation, soil samples were placed in flow-through chambers, NH2OH solution was added, and chambers were flushed continuously with pressurized air. N2O production was quantified, at a temporal resolution of 1 Hz, using quantum cascade laser absorption spectroscopy (Aerodyne Research, USA). Furthermore, isotope ratio mass spectrometry (Isoprime, UK) was used to analyze the isotopic signature of the produced N2O (i.e. δ15N, δ18O, and 15N site preference).We observed large differences in N2O emissions between different soils upon NH2OH addition. While a forest soil showed hardly any reaction to the addition of NH2OH, a very high and immediate formation of N2O was observed in a cropland soil. N2O production after NH2OH addition was also observed in autoclaved samples confirming an abiotic production. CO2 data additionally suggested an abiotic N2O production, as CO2 production was not enhanced by NH2OH addition to live soils. Laser spectrometry measurements revealed very fast reaction kinetics. An agricultural soil showed a turnover of about 50% in less than one hour. This proved that the fast reaction rate is also valid in soils. Further, isotopic signatures of N2O were used to identify underlying processes. The site preference of 15N in N2O is believed to be a powerful tool to disentangle different N2O production and consumption processes. We observed site preferences of about 33–36‰ in N2O emissions caused by NH2OH addition. This was in the same range as results found by Heil et al. (2014) for abiotic NH2OH oxidation as well as by Sutka et al. (2003) for nitrification. To find a dependence on soil properties, we correlated N2O emission rates after NH2OH addition with soil chemical properties. We found three primarily controlling factors of NH2OH induced N2O production in the following order: soil pH, C/N ratio, and Mn content. The combination of those could explain up to 90% of the variability of the N2O emissions caused by NH2OH addition. Soil pH showed the strongest correlation with N2O emission rates. This is explained by the higher stability of NH2OH (pKs 5.8) at lower pH due to increasing protonation. C/N ratio had a strongly negative correlation with N2O emission rates. Finally, Mn could oxidize free NH2OH to N2O. Although it was shown that NH2OH can also react with Fe3+ to form N2O (Bremner 1997), we could not find a correlation between Fe in soils and N2O emission rates. This can be explained by the higher redox potential of the MnO2/Mn2+ redox pair compared to the Fe3+/Fe2+ redox pair.Our results suggest a coupled biotic–abiotic production of N2O during nitrification. We showed that some soils have a very high potential to oxidize NH2OH so that abiotic N2O emissions in those soils seem only to be limited by NH2OH availability. We hypothesize that N2O production is the result of a leakage of the nitrification intermediate NH2OH, which acts as the substrate for abiotic oxidation to N2O in the soil matrix. N2O emissions during nitrification could then be explained as a function of nitrification rate and the combination of soil properties as mentioned above. However, further research is necessary to consolidate this relationship.Bremner JM 1997. Nutr Cycl Agroecosyst 49, 7-16Firestone MK and Davidson EA 1989. Exchange of trace gases between terrestrial ecosystems and the atmosphere. New York, USA. pp. 7-21Heil J, et al. 2014. submitted to Geochim Cosmochim ActaSutka RL, et al. 2003. Rapid Commun Mass Spectrom 17, 738-745 |