Contrasting regulating effects of soil available nitrogen, carbon, and critical functional genes on soil N 2 O emissions between two rice-based rotations

Aims Although the effects of upland and flooded rice cultivation on soil N 2 O emissions have been reported, scholars have not comparatively investigated the mechanism underlying N 2 O emissions during the rice cultivation seasons of rice-based rotation systems. Methods Herein, a two-year field experiment including two rice cultivation modes, namely, conventional upland rice–rapeseed (UR-CC) and flooded rice–rapeseed (RR-CC) rotations, was conducted to determine the effect of different rice plantation models on soil N 2 O emissions. Non-rice treatments (UR-NC and RR-NC) during the rice season were also implemented to confirm the effect of rice plantation or soil condition on N 2 O emissions. Results Seasonal N 2 O emissions were higher in UR-CC rotation than in RR-CC rotation (1.54 ± 0.16 vs . 0.71 ± 0.20 and 2.57 ± 0.28 vs. 0.76 ± 0.04 kg N ha -1 for the first and following rice cultivation seasons, respectively). Also, N 2 O emissions were higher in UR-NC treatment than that in RR-NC treatment during both rice seasons (2.45 ± 0.07 vs . 1.43 ± 0.35 and 3.74 ± 0.37 vs . 1.16 ± 0.08 kg N ha -1 , respectively). The yield-based N 2 O emissions were higher in the UR model than in the RR model (0.21 ± 0.01 vs . 0.10 ± 0.02 and 0.34 ± 0.03 vs. 0.11 ± 0.01, respectively). The responses of N 2 O emission fluxes to soil ammonium (NH 4 + ) and dissolved organic carbon (DOC) in UR rotation were stronger than those in RR rotation. Furthermore, total N 2 O emissions from non-rice treatments were higher than those from rice-cultivated treatments for both rice-based rotations. The increase in N 2 O emissions in UR-NC treatment could be attributed to the higher abundance of amoA gene and elevated soil mineral nitrogen content compared to UR-CC treatment. The higher amount of N 2 O generated in RR-NC treatment than that in RR-CC treatment was ascribed to the increased abundance of the nirS gene and the decreased abundance of the nosZ gene. The structural equation model supported that soil moisture, temperature, available C and N, and ammonium oxidation-related functional genes explained more than 70% of the effect on soil N 2 O emissions in UR rotation. Meanwhile, soil moisture, temperature, available N, and denitrification-related functional genes explained 80% of the effect in RR rotation. Conclusions These findings highlight the importance of rice plantation and their contribution to decreased field N 2 O emission, and suggest that soil available C, N, and critical functional genes should be considered when investigating N 2 O mitigation pathways during rice cultivation seasons.