Nitrous oxide (N₂O) is commonly known as laughing gas. But in view of its effect on environment, N₂O doesn’t live up to its name. N₂O gives rise to nitric oxide (NO) on reaction with oxygen atoms, and this NO in turn reacts with ozone. As a result, it is the main naturally occurring regulator of stratospheric ozone and is also a major greenhouse gas and air pollutant. Studies show that N₂O has 298 times more impact 'per unit weight' (Global warming potential) than carbon dioxide.

Although previous studies have revealed that soil physical and chemical conditions indirectly affect N₂O emission, people seldom notice microbial mechanisms of N₂O emission influenced by flooding and drying in paddy soils. Researchers in Institute of Subtropical Agriculture (ISA) tested two paddy soils which have grown double rice annual for more than a hundred years in Changsha of Hunan Province. They found that the N₂O flux was more significantly related to soil redox potential (Eh) than soil water content during the drying process. The RT-PCR results showed that both narG- and nosZ-containing denitrifiers had increased significantly after only one day of drying.

Furthermore, narG copy number varied following every flooding drying cycle, where drying caused an obvious increase and flooding caused a decrease in numbers. But the increase only occurred in first drying phase about nosZ copy number; further flooding-drying cycles did not cause any remarkable changes. And narG gene abundance showed a significant relationship to both Eh and water content, whereas nosZ was only significantly correlated to water content during the flooding drying process.

This study concluded that denittrifiers had shown different responses in flooding and drying cycles, and the narG-containing denitrifiers exhibited much more close correlation to the N₂O emission than nosZ-containing communities in the flooding-drying cycle in the paddy soils.

This work was financially supported by the Natural Science Foundation of China (41071181, 41090282) and the Chinese Academy of Sciences (KZCX2-YW-T07). The main findings of this study have published on Applied Soil Ecology, detail can be reached at http://www.sciencedirect.com/science/article/pii/S0929139312002168.