Effects of transient anaerobic conditions in the presence of acetylene on subsequent aerobic respiration and N2O emission by soil aggregates

Our objective was to assess the effect of anaerobic conditioning in the presence of acetylene on subsequent aerobic respiration and N2O emission at the scale of soil aggregates. Nitrous oxide production was measured in intact soil aggregates Δ (compacted aggregates without visible porosity) and Γ (aggregates with visible porosity) incubated under oxic conditions, with or without anaerobic conditioning for 6 d. N2O emissions were much higher in aggregates that had been submitted to anaerobic conditioning than in aggregates that did not experience this conditioning, although very little NO3− remained in soil after the anaerobic period. 15N isotope tracing technique was used to check whether N2O came from nitrification or denitrification. The results showed that denitrification was the major process responsible for N2O emissions. The aerobic CO2 production rate was also measured in intact soil aggregates. It was greater in aggregates submitted to anaerobic conditioning than in those that were not, suggesting that the anaerobic conditioning lead to an accumulation of small compounds including fatty acids that are readily available for microbial decomposition in aerobic conditions. This process increases the aerobic CO2 production and favours the N2O emissions through denitrification.