Remarkable N 2 O emissions by draining fallow paddy soil and close link to the ammonium-oxidizing archaea communities

Fallow paddies experience natural flooding and draining water status due to rainfall and evaporation, which could induce considerable nitrous oxide (N 2 O) emissions and need to be studied specially. In this study, intact soil columns were collected from a fallow paddy field and the flooding-draining process was simulated in a microcosm experiment. The results showed that both N 2 O concentrations in the soil and N 2 O emission rates were negligible during flooding period, which were greatly elevated by draining the fallow paddy soil. The remarkable N 2 O concentrations in the soil and N 2 O emission/h during draining both had significant relationships with the Arch-amoA gene ( P < 0.01) but not the Bac-amoA , narG , nirK , nirS , and nosZ genes, indicating that the ammonium-oxidizing archaea (AOA) might be the important players in soil N 2 O net production and emissions after draining. Moreover, we observed that N 2 O concentrations in the upper soil layers (0–10 cm) were not significantly different from that in the 10–20 cm layer under draining condition ( P > 0.05). However, the number of AOA and the nitrification substrate (NH 4 + -N) in the 0–10 cm layer were significantly higher than in the 10–20 cm layer ( P < 0.01), indicating N 2 O production in the 0–10 cm layer might be higher than the measured concentration and would contribute considerably to N 2 O emissions as shorter distance of gas diffusion to the soil surface.