Linkage of N2O emissions to the abundance of soil ammonia oxidizers and denitrifiers in purple soil under long-term fertilization

Abstract

Microbial nitrification and denitrification are responsible for the majority of soil nitrous (N2O) emissions. In this study, N2O emissions were measured and the abundance of ammonium oxidizers and denitrifiers were quantified in purple soil in a long-term fertilization experiment to explore their relationships. The average N2O fluxes and abundance of the amoAgene in ammonia-oxidizing bacteria during the observed dry season were highest when treated with mixed nitrogen, phosphorus and potassium fertilizer (NPK) and a single N treatment (N) using NH4HCO3as the sole N source; lower values were obtained using organic manure with pig slurry and added NPK at a ratio of 40%:60% (OMNPK),organic manure with pig slurry (OM) and returning crop straw residue plus synthetic NH4HCO3fertilizer at a ratio of 15%:85% (SRNPK). The lowest N2O fluxes were observed in the treatment that used crop straw residue(SR) and in the control with no fertilizer (CK). Soil NH4+provides the substrate for nitrification generating N2O as a byproduct. The N2O flux was significantly correlated with the abundance of the amoA gene in ammonia-oxidizing bacteria (r = 0.984, p < 0.001), which was the main driver of nitrification. During the wet season, soil nitrate (NO3−) and soil organic matter (SOC) were found positively correlated with N2O emissions (r = 0.774, p = 0.041 and r = 0.827, p = 0.015, respectively). The nirS gene showed a similar trend with N2O fluxes. These results show the relationship between the abundance of soil microbes and N2O emissions and suggest that N2O emissions during the dry season were due to nitrification, whereas in wet season, denitrification might dominate N2O emission.