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Objective To investigate the effects of the carbon-to-nitrogen ratio (C/N) on dissimilatory nitrate reduction pathways in paddy soil and clarify the competition between microbially mediated denitrification (DEN) and dissimilatory nitrate reduction to ammonium (DNRA), thus providing a theoretical basis for managing nitrogen fate through C/N regulation. Methods An anaerobic incubation experiment was conducted with paddy soil. Soil C/N was adjusted by applying different ratios of potassium nitrate (KNO3) and trisodium citrate (C6H5Na3O7). Two treatments C/N=5:1 and C/N=20:1 were established. The effects of C/N on nitrate reduction pathways were evaluated by measuring nitrous oxide (N2O) emissions and ammonium nitrogen (NH4+-N) accumulation. The 16S rRNA gene sequencing and bioinformatic analysis were employed to analyze the bacterial community structure under different C/N, thereby revealing the underlying microbial regulatory mechanisms. Results The high C/N treatment (C/N=20:1) showed significantly lower cumulative N2O release than the low C/N treatment (C/N=5:1), with the cumulative release being reduced by 32.87%. Furthermore, high C/N promoted NH4+-N accumulation, resulting in an increase of 276.61 mg/kg in NH4+-N accumulation compared with low C/N. Microbial analysis indicated that the C/N significantly influenced bacterial community structure, with higher C/N enhancing bacterial richness and diversity. In addition, high C/N increased the diversity of DNRA-associated bacteria (e.g., Anaeromyxobacter, Nitrospira, and Myxococcus), while suppressing the abundance of DEN-associated bacteria (e.g., Achromobacter and Pseudomonas). Network analysis further revealed that high C/N weakened the interspecific interactions among DEN-related bacteria, reducing the complexity and stability of their co-occurrence network, while promoting tighter and more stable interactions among DNRA-related bacteria. Conclusion The soil C/N was a key environmental factor governing the competition between DEN and DNRA in paddy soil. High C/N significantly reduced N2O emissions, promoted NH4+-N accumulation, reshaped the composition and interactions of functional bacteria (reducing the abundance of DEN-related bacteria and increasing the diversity of DNRA-related bacteria). This study provides theoretical support for understanding the microbially driven nitrogen retention mechanisms in soil and lays a foundation for developing novel fertilization strategies through C/N regulation.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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