Increased N2O emission due to paddy soil drainage is regulated by carbon and nitrogen availability.

• Drainage enhanced N 2 O emission via increased abundances of genes related to N 2 O production. • Labile C addition mitigated the increased N 2 O emission by drainage via increased nosZ abundance. • Nitrogen addition strongly amplified the increased N 2 O emission due to drainage. • N 2 O emission increased with NH 4 + depletion and NO 3 − accumulation following paddy soil drainage. • N 2 O emission was positively correlated with AOA and AOB abundances, and (nirK + nirS)/ nosZ ratio. Conversion from paddy field to upland cultivation, driven by economic benefits, generally increases N 2 O emission. However, the underlying mechanisms regarding the changes in N 2 O emission during the transition period of paddy soil drainage and conversion into upland remain unclear. To address this knowledge gap, a microcosm experiment was conducted to mechanistically elucidate the N 2 O emissions in response to paddy soil drainage and its interaction with carbon (C, glucose) and nitrogen (N, NH 4 Cl) availability. Results showed that N 2 O emissions were significantly lower in the submerged paddy soil (0.51 ± 0.03 mg N kg−1) compared to drained paddy soil (3.63 ± 0.66 mg N kg−1). The increased N 2 O emission was positively associated with soil NH 4 + depletion and NO 3 − accumulation, indicating increased nitrification and NO 3 − supply for denitrification following paddy soil drainage. Substrate C and N availability had little effect on N 2 O emission from submerged paddy soil, but strongly mediated the response of N 2 O emission to paddy soil drainage. High C availability largely mitigated the increased N 2 O emission by drainage, mainly resulting from increased N 2 O-reductase gene (nosZ) abundance. The increased N availability interacting with drainage strongly increased N 2 O emissions by 1.99–16.34 folds, primarily due to increased NO 3 − content and gene abundances of ammonia-oxidizing bacteria (AOB) and nitrite reductase (nirK and nirS). The N 2 O emissions were positively correlated with the abundances of ammonia-oxidizing archaea (AOA), AOB, nirK and nirS genes, and (nirK + nirS)/ nosZ ratio across treatments. Collectively, our findings suggested that the increased N 2 O emission due to paddy soil drainage is regulated by C and N availability, attributed to changes in NO 3 − content and abundances of nitrifying and denitrifying genes. [ABSTRACT FROM AUTHOR]