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 N 2 O from soil. However, studies on the effect of rice cropping on soil N 2 O 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 N 2 O emissions and key functional genes related to N 2 O-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 N 2 O 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 N 2 O emissions. No significant difference was found in the abundance of the aforementioned genes between two treatments. For both RF-CC and RF-NC treatments, N 2 O 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 N 2 O emissions. Increased transcripts of the AOA- amoA gene may facilitate N 2 O production and were confirmed by the positive linear relations between N 2 O 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 N 2 O emission for both treatments. These results implied that soil N 2 O 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. The patterns in N 2 O fluxes and seasonal cumulative N 2 O emission for rice planting and non-rice planting treatments during the whole experiment period under a double rice cropping-fallow system. The red and black arrows denote applying basal N fertilizer and N dressing, respectively. • Rice cultivation had no significant effect on N 2 O emission under a RF system. • Soil available N (DIN and MBN) as a key factor in controlling N 2 O emissions. • Increased transcripts of AOA- amoA gene may facilitate N 2 O production.