Effects of warming and fertilization on nirK-, nirS- and nosZ-type denitrifier communities in paddy soil

The effects of fertilization on soil denitrifying microorganisms are well-documented. However, the impact of global warming on these microorganisms, particularly regarding the interaction with fertilization, remains poorly understood. Here, a 4-year field warming experiment that included experimental warming (ET) and ambient temperature control (AC), with nitrogen (N) fertilizer applied (CF) or without N fertilizer (CK), was employed to assess the response of the abundance and community of nirK-, nirS- and nosZ- type denitrifiers to warming and fertilization in paddies, and to understand their relationship with potential denitrification rate (PDR). The results showed that warming amplified the positive effect of fertilization on abundance of nirK and nirS genes, while the abundance of nosZ remained unaffected. The copies of nirK and nirS under the ET-CF treatment were notably higher than in the other treatments. In the terms of biodiversity, warming diminished the effect of fertilization on the α-diversity of nirK and nirS, but it did not influence the α-diversity of nosZ. Besides, warming intensified the effect of fertilization on the β-diversity of nirK, while the β-diversity of nirS and nosZ remained unchanged in response to fertilization. Additionally, the community structure of denitrifiers varied with warming and/or fertilization. Specifically, Mesorhizobium (nirK), Proteobacteria (nirS) and Rhizobiales (nosZ) were dominant in AC-CK treatment. In the AC-CF treatment, Proteobacteria (nirK/S), Rhizobiales (nosZ) were the main taxa. For the ET treatments (ET-CF, ET-CK), Bradyrhizobiaceae (nirK), Proteobacteria (nirS) and Alphaproteobacteria (nosZ) were predominant. Correlation analysis revealed that soil pH, carbon and N content were the primary factors influencing nirK-, nirS-and nosZ- type denitrifiers. Moreover, PDR showed a positive relationship with nirK abundance, α-diversity of nosZ, and SOC. Overall, the results demonstrate that warming can modify the response of denitrifiers to fertilization, subsequently affecting denitrification rates, a phenomenon that merits attention.