Large variability in CO2 and N2 O emissions and in 15 N site preference of N2 O from reactions of nitrite with lignin and its derivatives at different pH

Jing Wei; Minghua Zhou; Harry Vereecken; Nicolas Brüggemann

doi:10.1002/rcm.7912

Large variability in CO₂ and N₂ O emissions and in ¹⁵ N site preference of N₂ O from reactions of nitrite with lignin and its derivatives at different pH

Rapid Commun Mass Spectrom. 2017 Aug 30;31(16):1333-1343. doi: 10.1002/rcm.7912.

Authors

Jing Wei¹, Minghua Zhou¹, Harry Vereecken¹, Nicolas Brüggemann¹

Affiliation

¹ Forschungszentrum Jülich GmbH, Agrosphere (IBG-3), Jülich, 52428, Germany.

PMID: 28557104
DOI: 10.1002/rcm.7912

Abstract

Rationale: Chemodenitrification is an important N₂ O source in soil; however, knowledge about the production of CO₂ and N₂ O from abiotic nitrite-SOM reactions, especially the N₂ O isotopic signatures (intramolecular ¹⁵ N site preference (SP), and δ¹⁵ N^bulk and δ¹⁸ O values), is quite limited at present.

Methods: N₂ O and CO₂ emissions from chemical reactions of nitrite with lignin products were determined with gas chromatography, and their response surfaces as a function of pH from 3 to 6 and nitrite concentration from 0.1 to 0.5 mM were explored with polynomial regression. The intramolecular ¹⁵ N distribution of N₂ O, as well as δ¹⁵ N^bulk and δ¹⁸ O values, were measured with an isotope ratio mass spectrometer coupled to an online pre-concentration unit. The variability in N₂ O SP values was tested from pH 3 to 5, and for nitrite concentrations from 0.3 to 0.5 mM.

Results: Both CO₂ and N₂ O emissions varied largely with pH and the structure of lignin products. The highest N₂ O emission occurred at pH 4-5 in 4-hydroxy-3,5-dimethoxybenzaldehyde and 4-hydroxy-3,5-dimethoxybenzoic acid treatments, and at pH 3 in the treatments with lignin, 4-hydroxy-3-methoxybenzaldehyde, 4-hydroxy-3-methoxybenzoic acid, 4-hydroxybenzaldehyde, and 4-hydroxybenzoic acid. A wide range of N₂ O SP values (11.9-37.4‰), which was pH dependent and not distinguishable from microbial pathways, was observed at pH 3-5. The δ¹⁵ N^bulk and δ¹⁸ O values of N₂ O were both in a similar range to that reported for fungal denitrification and bacterial denitrification.

Conclusions: These results present the first characterization of the isotopic composition of N₂ O from chemodenitrification in pure chemical assays. Chemical reactions of nitrite with lignin are pH-dependent and associated with substantial CO₂ and N₂ O emissions. The SP values of N₂ O derived from chemodenitrification were neither distinguishable from the biotic pathways nor remained stable with varying pH. Therefore, the use of N₂ O isotopic signatures for source partitioning is restricted when chemodenitrification is contributing significantly to N₂ O emission.