Fertilizer types shaped the microbial guilds driving the dissimilatory nitrate reduction to ammonia process in a Ferralic Cambisol

Dissimilatory nitrate reduction to ammonia (DNRA) is one of the three processes of soil nitrate reduction. However, relationships between DNRA microbes and nutrient fertilization are poorly known. We studied the DNRA microbial community in a Ferralic Cambisol containing plots including control without fertilization, swine manure fertilization (M), chemical fertilization (NPK), and chemical/manure combined fertilization (MNPK) treatments. The abundance of DNRA microbes, represented by the nrfA gene abundance, ranged from 2 x 10(7) to 5.8 x 10(7) g(-1) dry soil and was positively correlated with soil moisture and total phosphorus (TP) and negatively correlated with NH4+ and total potassium (TK). The potential DNRA rate ranged from 0.5 to 1.5 mu g N g(-1) dry soil h(-1). The alpha-diversity of the DNRA bacteria increased in the M-treated plots, and the dominant DNRA bacterial OTUs were assigned to the phyla Proteobacteria, Verrucomicrobia and Acidobacteria. PCoA and redundancy analysis indicated that the composition of the DNRA bacteria was strongly impacted by the long-term fertilization regimes and was associated with pH, TN, TP and TC followed by moisture, NH4+ and C/NO3-. Interestingly, the composition of the DNRA bacterial community, the properties of the soil (TP, AK and C/N) and the interactions of these factors (soil properties x DNRA composition) explained the DNRA rate. Collectively, these data suggested that the DNRA potential in the Ferralic Cambisol is possibly controlled by the stoichiometry of macronutrient and the composition of DNRA microbes but not their total abundance.