Partial substitution of chemical fertilizer by organic materials changed the abundance, diversity, and activity of nirS-type denitrifying bacterial communities in a vegetable soil

The nirS gene encodes nitrite reductase (NIR) and participates in the denitrification of inorganic nitrogen (N) in soils. Although the gene is important in the global cycling of N, little is known about the responses of nirS-denitrifier communities to the substitution of chemical fertilizer by organic materials. Therefore, a field experiment in a vegetable soil was established with only chemical fertilizer (F) and four partially substituted organic materials treatments: straw (SF), mushroom dregs (MF), biochar (BF), and cattle manure (CF). All treatments received equal amounts of total nitrogen, phosphorus, and potassium. Integrated high-throughput absolute abundance quantification (iHAAQ) was used to quantify the abundance of the nirS gene in denitrifier communities. The relations among NIR activity, N fractions and other soil properties were also evaluated. Compared with the F treatment, the substitution with organic materials increased the diversity but reduced the absolute abundance of the nirS gene, particularly in the SF treatment (P < 0.05). The NIR activity increased in F, SF, and BF treatments, with the highest value (8.14 mu mol d(-1) g(-1)) in the BF treatment. In a distance-based redundancy analysis, the composition of the nirS-denitrifier community was significantly correlated with the soil C:N ratio. The NIR activity was significantly correlated with soil N:P ratio (r = 0.486, P < 0.05). Overall, the biochar substitution increased the diversity of nirS-denitrifiers and NIR activity. The substitution of chemical fertilizer by various organic materials changed the nirS community, because the changes in soil properties, especially the interaction of carbon and nitrogen, affected different genera of bacterial.