Response of nitrifying and denitrifying functional genes and microbial community structure to experimental warming

Climate warming has been hypothesized to influence nitrous oxide (N2O) emission from soil, however the direct impact of soil warming on abundance of nitrifying and denitrifying functional genes and microbial community structure are unclear. In this study we examined the impact of experimental warming on abundance of nitrifying and denitrifying bacteria and diversity of microbial community in soil. Soil samples collected from wheat field with simulated warming (W) and non-warming (NW) under regular (RI) and high irrigation (HI) within soil profile (5 cm, 10 cm, and 20 cm). The nitrifier (amoA) and denitrifier (nirK, nirS, nosZ) gene abundance was analyzed by real-time quantitative PCR and microbial community structure was monitored by 16S rRNA analysis. Results showed that the warming significantly increased amoA gene copy number than non-warming at in both irrigation treatments at 5 cm soil layer in W-RI, and 5 cm and 10 cm soil depth in W-HI, respectively and subsequently increased nitrate accumulation in soil, however soil warming significantly decreased nirS and nirK and increased nosZ gene copy number. Though the warming decreased denitrifiers genes, the N2O production rate was high in warming when compared with non-warming in both irrigation treatment, but the high N2O production in W-RI treatment could be due to the inhibition of nitrous oxide reductase enzyme by more oxic condition which is produced by warming. Conclusively, warming increased nitrifiers and decreased denitrifiers gene abundance in soil when compared with non-warming.