Abstract: The reduction of nitric oxide (N₂O) to dinitrogen (N₂) in denitrification is performed by the nosZtype denitrifying bacteria, which plays a key role in regulating N₂O emission. To verify the effects of fertilization on the nosZtype denitrifying bacterial communities in paddy soils, realtime PCR and highthroughput sequencing approaches were applied to investigate the abundance and structure of the nosZtype denitrifying bacterial communities in a 30year fertilized paddy soil in Hunan Province, China. The abundances of nosZ gene ranged from 2.14×10⁸ to6.09×10⁸ copies·g^-1 dry soil. ThenosZ gene abundances in the fertilized treatments (chemical fertilizer, 70% chemical fertilizer + 30% organic manure, and 40% chemical fertilizer + 60% organic manure) were 47.3%-64.8% lower than that of CK (P<0.01). Organic manure application rates rarely affected the nosZ gene abundance. Proteobacteria was the predominant phylum, accounting for 60.2%-77.5% of the total reads. Bacteria_unclassified, Proteobacteria_unclassified, Betaproteobacteria_unclassified, and Rhizobiales were the abundant order groups that represented 93.6%-95.9% of the total reads. Fertilization significantly decreased the Proteobacteria_unclassified abundances (P<0.01) and significantly increased the relative abundance of Rhizobiales, environmental_samples, and Rhodocyclales in the fertilized soils compared with CK (P<0.05). Fertilization altered the nosZtype denitrifying bacterial community structure. Organic manure application rates had minor effects on the community structure. All the examined soil properties, expect for C/N ratio, were significantly correlated with the abundance, relative abundance of some order groups and structure of the nosZtype denitrifying bacterial communities, with nitrate and soil pH were the most important factors affecting the nosZtype denitrifying bacterial community structure. These results indicated that fertilization significantly changed the abundance and structure of the nosZtype denitrifying bacterial communities, while organic manure application rates showed limited effect. Our results provided basis for further research on the effects of fertilization on the denitrifying bacterial community.

Key words: vegetation, landscape, health assessment, island, Changshan Archipelago.