Comammox Nitrospira and AOB communities are more sensitive than AOA community to different fertilization strategies in a fluvo-aquic soil

Ammonia oxidizing archaea (AOA), ammonia oxidizing bacteria (AOB) and the newly discovered complete ammonia oxidizers (comammox Nitrospira) are responsible for ammonia oxidation, which is the first and rate-limiting step of nitrification. A better understanding of the complex responses of AOA, AOB and comammox Nitrospira to inorganic and organic fertilization regimes is critical to get the whole picture of soil nitrification. Here, we investigated the abundances and community compositions of AOA, AOB and comammox Nitrospira in a fluvo-aquic soil under different fertilization strategies: nitrogen fertilizer reduction treatments (CK, PK, 50 % NPK and 75 % NPK), conventional fertilizer treatment (100 % NPK), N fertilizer reduction with organic manure substitution treatments (25 % OMNPK, 50 % OMNPK, 100 % OMPK and 200 % OMPK). The results indicated that 100 % NPK treatment significantly increased AOB abundance, while the abundances of AOA and comammox Nitrospira were enhanced significantly by 100 % and 200 % OMPK treatments. Principal coordinate analysis indicated different fertilization strategies had greater effect on the communities of AOB and comammox Nitrospira than those of AOA. Fertilizer application (other than CK) decreased the relative abundance of Nitrosospira cluster 3b of AOB while increased the relative abundance of Nitrosospira cluster 3a.2. Fertilizer, especially high manure application increased the relative abundance of comammox Nitrospira clade A.2 but decreased the relative abundance of clade B. Both redundancy analysis and mantel test showed AOB and comammox Nitrospira communities were regulated by more soil factors than AOA community. These results suggested the communities of AOB and comammox Nitrospira were more sensitive than AOA community to different fertilization strategies in a fluvo-aquic soil of northern China.