Interactive effects of MnO2, organic matter and pH on abiotic formation of N2O from hydroxylamine in artificial soil mixtures

Shurong Liu,Nicolas Brüggemann,Anne E. Berns,Di Wu,Harry Vereecken

doi:10.1038/srep39590

Shurong Liu, Nicolas Brüggemann + Show 3 more

Open Access

https://doi.org/10.1038/srep39590

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Journal: Scientific Reports	Publication Date: Feb 1, 2017
Citations: 21	License type: open-access

Affiliation: Forschungszentrum Jülich

Abstract

Abiotic conversion of the reactive nitrification intermediate hydroxylamine (NH2OH) to nitrous oxide (N2O) is a possible mechanism of N2O formation during nitrification. Previous research has demonstrated that manganese dioxide (MnO2) and organic matter (OM) content of soil as well as soil pH are important control variables of N2O formation in the soil. But until now, their combined effect on abiotic N2O formation from NH2OH has not been quantified. Here, we present results from a full-factorial experiment with artificial soil mixtures at five different levels of pH, MnO2 and OM, respectively, and quantified the interactive effects of the three variables on the NH2OH-to-N2O conversion ratio (RNH2OH-to-N2O). Furthermore, the effect of OM quality on RNH2OH-to-N2O was determined by the addition of four different organic materials with different C/N ratios to the artificial soil mixtures. The experiments revealed a strong interactive effect of soil pH, MnO2 and OM on RNH2OH-to-N2O. In general, increasing MnO2 and decreasing pH increased RNH2OH-to-N2O, while increasing OM content was associated with a decrease in RNH2OH-to-N2O. Organic matter quality also affected RNH2OH-to-N2O. However, this effect was not a function of C/N ratio, but was rather related to differences in the dominating functional groups between the different organic materials.

Highlights

Abiotic reactions of Soil organic matter (SOM) and inorganic N may contribute to the quick disappearance, as nitrite and nitrate can react with SOM or dissolved organic carbon (DOC), leading to the formation of organic N, such as nitroso and nitro compounds[21,22], while NH2OH can react with carbonyl groups to form oximes[23,24]: R1(R2)C = O + NH2OH → R1(R2)C = NOH + H2O
The RNH2OH-to-N2O increased greatly with an increase in MnO2 content from 0% to 0.1% (Fig. 2). This finding is consistent with Bremner et al.[5], who studied 19 soils with a wide range of properties and found that the formation of N2O by decomposition of NH2OH was highly correlated with oxidized Mn content of the soils
The fact that NH2OH was used in the past for the selective extraction of Mn oxides from soil samples[35] indicates that NH2OH can efficiently reduce Mn(IV) to Mn(II) or Mn(III) in natural soil samples

Summary

Introduction

The latter was found for Nitrosomonas europaea under oxic conditions, both for wild-type N. europaea and even more so for NirK and NorB-deficient mutants[10] In accordance with this assumption, a positive relationship between NH2OH content of the soil and soil N2O emissions under oxic conditions has been detected in www.nature.com/scientificreports/. High soil N2O emissions have been observed in acid forest soils[29,30]. Chemical reactions that produce N2O in the soil, such as the reaction of nitrite with SOM and the reaction of NH2OH with MnO2, are subject to a strong pH dependence and can contribute substantially to N2O emissions under acidic conditions[32,33,34]

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