Peatlands are an important source of nitrous oxide (N2O) emissions, which is a potent greenhouse gas and is also involved in the depletion of stratospheric ozone. Due to the large number of N2O production and consumption processes, it is challenging to trace N2O emissions to an individual process. We investigated the effect of different water regimes (dry, intermediate and flooded) on N2O emissions via 15N tracing in a microcosm study with well-decomposed nitrogen-rich alluvial fen peat. The isotopic composition of the peat and emitted N2O gas was analysed in combination with qPCR analysis of abundances and diversity of N-cycle functional genes. Bacterial denitrification was the predominant source of N2O emission, followed by nitrification (ammonia oxidation). This was identified by a close relationship between 15N-N2O and 15N-NO3− under flooded (anoxic) and intermediate (sub-oxic) treatments and concomitant increases in nirK, nirS and nosZ after the flooding. The site preference and δ18O values fell within the previously observed range indicating multiple overlapping processes and bacterial denitrification as the dominant process. Although the combination of isotopic and microbial analyses indicates that bacterial denitrification is the primary process under intermediate and flooded treatments, the high abundance of amoA indicates that nitrification via comammox was present. High archaeal amoA and bacterial amoA gene copy numbers and second highest N2O emissions under the intermediate and flooded peats indicated that ammonia oxidation was, secondary to denitrification, also a source for N2O. The increase in emissions with nrfA gene copies also showed that dissimilatory nitrate reduction to ammonium (DNRA) potentially contributed to N2O emission under flooded treatment.
Bibliographical noteFunding Information:
The research was supported by the Ministry of Education and Research of Estonia (PRG‐352 and MOBERC20 grants), the EU through European Regional Development Fund (ENVIRON and EcolChange Centres of Excellence, and the MOBTP101 returning researcher grant by Mobilitas +), and the Estonian Centre of Analytical Chemistry (AKKI). The methodological groundwork for the study was laid by IAEA’s Coordinated Research Project (CRP) on “Strategic placement and area‐wide evaluation of water conservation zones in agricultural catchments for biomass production, water quality and food security”. Dr. Reinhald Well’s laboratory at Johann Heinrich von Thünen Institute, Braunschweig, Germany provided gas samples for calibration of IRM-MS. We also thank Margarita Oja for the assistance in gas sampling. The datasets generated during the current study are not publicly available due to lack of agreement with participating outside labs but are available from the corresponding author on reasonable request.
Data Availability StatementEnquiries about data availability should be directed to the authors.
- N tracer
- Site preference
- Soil oxygen