Abstract
Fallow paddies experience natural flooding and draining water status due to rainfall and evaporation, which could induce considerable nitrous oxide (N2O) 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 N2O concentrations in the soil and N2O emission rates were negligible during flooding period, which were greatly elevated by draining the fallow paddy soil. The remarkable N2O concentrations in the soil and N2O 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 N2O net production and emissions after draining. Moreover, we observed that N2O 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 (NH4+-N) in the 0–10 cm layer were significantly higher than in the 10–20 cm layer (P < 0.01), indicating N2O production in the 0–10 cm layer might be higher than the measured concentration and would contribute considerably to N2O emissions as shorter distance of gas diffusion to the soil surface.
Highlights
Nitrous oxide (N2O), one of the important contributors to the radiative forcing by greenhouse gasses (GHGs), is expected to remain the largest emission throughout the 21st century and greatly contributes to stratospheric ozone destruction[1]
The peak N2O emission, which occurred on draining day 15, was 1204.81 μg m−2 h−1 and the levels continued to decrease during the following drainage period
Different water conditions affect the biogeochemistry of paddy soils with respect to N2O production and emission[24]
Summary
Nitrous oxide (N2O), one of the important contributors to the radiative forcing by greenhouse gasses (GHGs), is expected to remain the largest emission throughout the 21st century and greatly contributes to stratospheric ozone destruction[1]. Other studies have shown that the abundance of nitrifiers (Arch-amoA and Bac-amoA gene) in draining paddy soil was considerably more than that in flooded soil, and amoA gene abundance was significantly correlated to N2O emission rates[12,18] These varying results imply that the importance of nitrifiers, denitrifiers, or both to N2O emission in draining paddy soil might differ between cases. Without human management, the soil water conditions of fallow paddies mainly depend on the rainfall and atmospheric evaporation, resulting in fluctuations in soil moisture of fallow paddies Such prolonged periods and great variation in soil water condition would induce considerable N2O emissions from fallow paddy fields. Studies on the microbial process and regulatory mechanisms of N2O production and emission under different water status in fallow paddy soil are scarce
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