Variations of the nirS-, nirK-, and nosZ-denitrifying bacterial communities in a northern Chinese soil as affected by different long-term irrigation regimes.

Denitrification causes nitrogen loss from agricultural soils and emission of nitrous oxide (N2O). Water addition leads to an increase in soil moisture which greatly influenced soil denitrification. However, it is unclear how irrigation management affected the denitrifying bacterial communities in agricultural systems. In the present study, we investigated the abundance, diversity, and composition of the nirS-, nirK-, and nosZ-denitrifying bacterial communities in the soil under different long-term irrigation regimes by using real-time PCR (qPCR) and Illumina MiSeq sequencing approaches. Results showed that the abundance of nosZ gene was 3.94-6.01 and 35.09-60.21 times more than that of nirS and nirK genes, and the abundance of nirS gene was 5.84-15.30 times higher than that of nirK gene, respectively, in different irrigation treatments. However, the Alpha diversity indices of the nirK-denitrifying bacterial community were higher than those of the nirS- and nosZ-denitrifying bacterial communities. Proteobacteria was the predominant phylum for all the denitrifying bacterial communities, and significant differences were observed in relative abundance of Alphaproteobacteria and Betaproteobacteria in predominant class between different irrigation treatments for the nirS- and nosZ-denitrifying bacterial communities, respectively. Irrigation significantly affected the abundance, Shannon and Invsimpson indices, and structure of the nirS- and nosZ-denitrifying bacterial communities, whereas it only minor influenced the structure of the nirK-denitrifying bacterial community. Furthermore, the shifts in abundance, diversity, and structure of the nirS- and nosZ-denitrifying bacterial communities correlated significantly with the soil property variations; however, no soil property was significantly correlated with the abundance and Alpha diversity index of the nirK-denitrifying bacterial community. Our results demonstrate that different long-term irrigation regimes greatly altered the abundance, diversity, and structure of the nirS- and nosZ- rather than the nirK-denitrifying bacterial communities.