Denitrification and nitrification are two pivotal microbial processes relating to N
2O emissions. However, the difference in N
2O emission fluxes and N
2O-producing bacteria between a karst (KA) and non-karst area (NKA) remains unclear. The objective of this study is to compare the differences in soil N
2O emissions, nitrifying bacteria, and denitrifying bacteria during the growth period of rice in KA and NKA, and to explore the mechanisms by which microorganisms and environmental factors drive N
2O emissions. Here, N
2O emission fluxes of paddy fields were collected using the static dark chamber and measured using gas chromatography at KA and NKA in the Maocun Karst Experimental Site in Guilin, China. The nitrifying bacteria (ammonia-oxidizing bacteria, AOB) and denitrifying bacteria (
nirK-denitrifier) were determined using real-time PCR and high-throughput sequencing, respectively. Results showed that during the rice growth period, the N
2O emission fluxes in KA was generally lower than that in NKA, with cumulative N
2O emissions of −0.054 and 0.229 kg·hm
−2 in KA and NKA, respectively. The absolute abundance of AOB in KA (8.91 × 10
6–2.68 × 10
7 copies·g
−1) was significantly higher than that in NKA (1.57 × 10
6–6.48 × 10
6 copies·g
−1), while the absolute abundance of
nirK-denitrifier had no significant difference between the two areas. The composition and diversity of AOB and
nirK-denitrifier differed significantly between KA and NKA. Results from partial least squares structural equation modeling (PLS-SEM) indicated that soil properties, carbon sources, and nitrogen sources had positive effects on AOB and
nirK-denitrifier, while
nirK-denitrifier had a negative effect on N
2O emissions. Partial least squares regression (PLSR) predictions revealed that NO
3−-N, SOC, TN, Mg
2+, Ca
2+, and pH were the most important factors influencing N
2O emission fluxes. This study highlights the critical role of the typical characteristics of KA soils in reducing N
2O emissions from paddy fields by driving the evolution of AOB and
nirK-denitrifier.
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