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.