An improved 15N tracer approach to study denitrification and nitrogen turnover in soil incubations

摘要

Rationale: Denitrification (the reduction of oxidized forms of inorganic N to N2O and N2) from upland soils is considered to be the least well understood process in the global N cycleDenitrification from upland soils is considered to be the least well understood process in the global N cycle due to methodical constraints of existing methods. . The main reason for this lack of understanding is that the terminal product (N2) of denitrification is extremely difficult to measure against the hugelarge atmospheric background.ududMethods: Here wWe describe a system that combines the 15N-tracer technique with a 40-fold reduced N2 (2 % v/v) atmosphere in a fully automated incubation set up for direct quantification of N2 and N2O emissions. The system was tested on a pasture soil from sub-tropical Australia under different soil moisture conditions and combined with 15N tracing in extractable soil N pools to establish a full N balance. ududResults: The method proved to be highly sensitive for detecting N2 (1.12 µg N h-1 kg-1ds1 dry soil (ds)) and N2O (0.36 µg N h-1 kg 1 ds) emissions. The main end-product of denitrification in the investigated soil was N2O for both water contents with N2 accounting for only 3% to13% of the total denitrification losses. Between 90-95% of the added 15N fertiliser could be recovered in N gases and extractable soil N pools. ududConclusions: These high and N2O-dominated denitrification rates found in this study are pointing at both a high ecological and agronomic importance of denitrification in subtropical pasture soils. The new system allows for a direct and highly sensitive detection of N2 and N2O fluxes from soils and may help to significantly improve our mechanistic understanding of N cycling and denitrification in terrestrial agro-ecosystems.