科研之友
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摘要
RationaleDenitrification (the reduction of oxidized forms of inorganic nitrogen (N) to N2O and N-2) 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 (N-2) of denitrification is extremely difficult to measure against the large atmospheric background. MethodsWe describe a system that combines the N-15-tracer technique with a 40-fold reduced N-2 (2% v/v) atmosphere in a fully automated incubation setup for direct quantification of N-2 and N2O emissions. The N-15 values of the emitted N-2 and N2O 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 N-15 tracing in extractable soil N pools to establish a full N balance. ResultsThe method proved to be highly sensitive for detecting N-2 (1.12gNh(-1)kg(-1) dry soil (ds)) and N2O (0.36gNh(-1)kg(-1) ds) emissions. The main end product of denitrification in the investigated soil was N2O for both water contents, with N-2 accounting for only 3% to 13% of the total denitrification losses. Between 90 and 95% of the added N-15 fertiliser could be recovered in N gases and extractable soil N pools. ConclusionsThe high and N2O-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 N-2 and N2O fluxes from soils and may help to significantly improve our mechanistic understanding of N cycling and denitrification in terrestrial agro-ecosystems.
- 出版日期2016-9-30
