Responses of nitrification and denitrification in the rhizosphere of mudflat paddy to rice genotype and nitrogen fertilization

Nitrification and denitrification are important processes in the biogeochemical cycle in agricultural soils and are influenced by plant genotype and nitrogen (N) fertilization. However, few studies have evaluated the effects of genotype on nitrification and denitrification in the rhizosphere of rice cultivated in mudflats and their response to N fertilization. In this study, we determined the net nitrification and denitrification rates, quantified the abundance of functional genes involved in nitrification and denitrification, and characterized bacterial communities in the rhizosphere of two rice varieties (japonica and hybrid rice) cultivated in mudflat soil with three N fertilization levels. Results showed that net nitrification rates were strongly influenced by genotype and was higher in the rhizosphere of hybrid rice than in that of japonica rice, which might be related to the N absorption strategy of rice, while net denitrification rates were mainly affected by N fertilization. Unlike hybrid rice, the net nitrification rate in the rhizosphere of japonica rice was strongly influenced by N fertilization and positively correlated to N fertilization levels. In contrast, the net denitrification rate of hybrid rice was strongly influenced by N fertilization and positively correlated to N fertilization levels, while N fertilization had no significant effect on the net denitrification rate of japonica rice. Ammonia-oxidizing bacteria were the main drivers of nitrification in the rhizosphere, and denitrification in the rhizosphere of hybrid rice was mainly driven by nar G-, nir S-, and nor B-type denitrifiers. Furthermore, differences in the assemblages of bacteria associated with the relative abundance of these functional genes provided insight into genotypic differences in nitrification and denitrification responses to N fertilization. Overall, this study provides insight into the underlying mechanisms of nitrification and denitrification influenced by rice genotypes and N fertilization in the rhizospheres of japonica and hybrid rice.