Available nitrogen and ammonia-oxidizing archaea in soil regulated N2O emissions regardless of rice planting under a double rice cropping-fallow system

Changing redox conditions in paddy fields due to more frequent events govern the soil biogeochemical processes that further affect the generation and emission of N2O from soil. However, studies on the effect of rice cropping on soil N2O emission under rice-growing seasons and relevant mechanisms are scarce. A double rice cropping-fallow (RF) field in central China, with rice cropping (RF-CC) and non-rice cropping (RF-NC) cultivation, were selected to investigate that effect of rice planting on soil N2O emissions and key functional genes related to N2O-production and consumption, such as the ammonia-monooxygenase gene derived from ammonia-oxidizing archaea (AOA-amoA) and ammonia-oxidizing bacteria (AOB-amoA) and nitrous oxide reductase gene (nosZ). The results of the static opaque chamber-gas chromatography technique showed that seasonal cumulative N2O emissions from RF-NC treatment during the first and second rice growing season were 1.02 ± 0.17 and 2.95 ± 0.12 kg N ha−1, respectively, and were comparable to those from RF-CC treatment (0.82 ± 0.09 and 2.97 ± 0.18 kg N ha−1, respectively), indicating rice cropping had no crucial effect on soil N2O emissions. No significant difference was found in the abundance of the aforementioned genes between two treatments. For both RF-CC and RF-NC treatments, N2O fluxes were positively correlated with the soil available nitrogen, such as dissolved inorganic N (DIN) and microbial biomass N (MBN), suggesting that soil available N was a key factor controlling N2O emissions. Increased transcripts of the AOA-amoA gene may facilitate N2O production and were confirmed by the positive linear relations between N2O fluxes and the abundance of AOA-amoA gene for both treatments. The structural equation model (SEM) indicated that both soil available N and AOA-amoA gene contributed more than 70% to their effects on N2O emission for both treatments. These results implied that soil N2O emissions during therice-growing period could be regulated by the interaction of soil parameters and related functional genes, rather than the effect of rice cropping under a RF system.