The fate of N2O consumed in soils

B. Vieten, F. Conen, B. Seth, C. Alewell
Soils are capable to consume N 2 O. It is generally assumed that consumption occurs exclusively via respiratory reduction to N 2 by denitrifying organisms (i.e. complete denitrification). Yet, we are not aware of any verification of this assumption. Some N 2 O may be assimilatorily reduced to NH 3 . Reduction of N 2 O to NH 3 is thermodynamically advantageous compared to the reduction of N 2 . Is this an ecologically relevant process? To find out, we treated four contrasting soil samples in a
more » ... soil samples in a flow-through incubation experiment with a mixture of labelled (98%) 15 N 2 O (0.5-4 ppm) and O 2 (0.2-0.4%) in He. We measured N 2 O consumption by GC-ECD continuously and δ 15 N of soil organic matter before and after an 11 to 29 day incubation period. Any 15 N 2 O assimilatorily reduced would have resulted in the enrichment of soil organic matter with 15 N, whereas dissimilatorily reduced 15 N 2 O would not have left a trace. None of the soils showed a change in δ 15 N that was statistically different from zero. A maximum of 0.27% (s.e. ±0.19%) of consumed 15 N 2 O may have been retained as 15 N in soil organic matter in one sample. On average, 15 N enrichment of soil organic matter during the incubation may have corresponded to a retention of 0.019 % (s.e. ±0.14%; n=4) of the 15 N 2 O consumed by the soils. We conclude that assimilatory reduction of N 2 O plays, if at all, only a negligible role in the consumption of N 2 O in soils.
doi:10.5451/unibas-ep9409 fatcat:iwtv52xiyjfalmaijsnjbtcspm