Clemens Scheer1, Rudolf Meier2, Nicolas Brüggemann3, Peter R Grace1, Michael Dannenmann2. 1. Institute for Future Environments, Queensland University of Technology, Brisbane, QLD, 4000, Australia. 2. Karlsruhe Institute of Technology - Institute of Meteorology and Climate Research, Kreuzeckbahnstraße 19, 82467, Garmisch-Partenkirchen, Germany. 3. Forschungszentrum Jülich, Institute of Bio- and Geosciences - Agrosphere (IBG-3), Wilhelm-Johnen-Straße, 52428, Jülich, Germany.
Abstract
RATIONALE: Denitrification (the reduction of oxidized forms of inorganic nitrogen (N) to N2 O and N2 ) from upland soils is considered to be the least well-understood process in the global N cycle. The main reason for this lack of understanding is that the terminal product (N2 ) of denitrification is extremely difficult to measure against the large atmospheric background. METHODS: We describe a system that combines the (15) N-tracer technique with a 40-fold reduced N2 (2% v/v) atmosphere in a fully automated incubation setup for direct quantification of N2 and N2 O emissions. The δ(15) N values of the emitted N2 and N2 O were determined using a custom-built gas preparation unit that was connected to a DELTA V Plus isotope ratio mass spectrometer. The system was tested on a pasture soil from sub-tropical Australia under different soil moisture conditions and combined with (15) N tracing in extractable soil N pools to establish a full N balance. RESULTS: The method proved to be highly sensitive for detecting N2 (1.12 μg N h(-1) kg(-1) dry soil (ds)) and N2 O (0.36 μg N h(-1) kg(-1) ds) emissions. The main end product of denitrification in the investigated soil was N2 O for both water contents, with N2 accounting for only 3% to 13% of the total denitrification losses. Between 90 and 95% of the added (15) N fertiliser could be recovered in N gases and extractable soil N pools. CONCLUSIONS: The high and N2 O-dominated denitrification rates found in this study are pointing at both the high ecological and the agronomic importance of denitrification in subtropical pasture soils. The new system allows for a direct and highly sensitive detection of N2 and N2 O fluxes from soils and may help to significantly improve our mechanistic understanding of N cycling and denitrification in terrestrial agro-ecosystems.
RATIONALE: Denitrification (the reduction of oxidized forms of inorganic nitrogen (N) to N2 O and N2 ) from upland soils is considered to be the least well-understood process in the global N cycle. The main reason for this lack of understanding is that the terminal product (N2 ) of denitrification is extremely difficult to measure against the large atmospheric background. METHODS: We describe a system that combines the (15) N-tracer technique with a 40-fold reduced N2 (2% v/v) atmosphere in a fully automated incubation setup for direct quantification of N2 and N2 O emissions. The δ(15) N values of the emitted N2 and N2 O were determined using a custom-built gas preparation unit that was connected to a DELTA V Plus isotope ratio mass spectrometer. The system was tested on a pasture soil from sub-tropical Australia under different soil moisture conditions and combined with (15) N tracing in extractable soil N pools to establish a full N balance. RESULTS: The method proved to be highly sensitive for detecting N2 (1.12 μg N h(-1) kg(-1) dry soil (ds)) and N2 O (0.36 μg N h(-1) kg(-1) ds) emissions. The main end product of denitrification in the investigated soil was N2 O for both water contents, with N2 accounting for only 3% to 13% of the total denitrification losses. Between 90 and 95% of the added (15) N fertiliser could be recovered in N gases and extractable soil N pools. CONCLUSIONS: The high and N2 O-dominated denitrification rates found in this study are pointing at both the high ecological and the agronomic importance of denitrification in subtropical pasture soils. The new system allows for a direct and highly sensitive detection of N2 and N2 O fluxes from soils and may help to significantly improve our mechanistic understanding of N cycling and denitrification in terrestrial agro-ecosystems.
Authors: Daniel I Warner; Clemens Scheer; Johannes Friedl; David W Rowlings; Christian Brunk; Peter R Grace Journal: Sci Rep Date: 2019-07-31 Impact factor: 4.379
Authors: Johannes Friedl; Clemens Scheer; David W Rowlings; Evi Deltedesco; Markus Gorfer; Daniele De Rosa; Peter R Grace; Christoph Müller; Katharina M Keiblinger Journal: Sci Rep Date: 2020-02-12 Impact factor: 4.379