Nitrification inhibitor chlorate and nitrogen substrates differentially affect comammox Nitrospira in a grassland soil

Abstract

The results showed that the application of chlorate inhibited the oxidation of both NH₄⁺ and NO₂^- in all three nitrogen treatments. The application of chlorate significantly reduced the abundance of comammox <i>Nitrospira amo</i>A and <i>nxr</i>B genes across the 90-day experimental period. Chlorate also had a significant effect on the beta diversity (Bray-Curtis dissimilarity) of the comammox <i>Nitrospira</i> clade B community. Whilst AOB grew in response to the N substrate additions and were inhibited by both inhibitors, AOA showed litle or no response to either the N substrate or inhibitor treatments. In contrast, comammox <i>Nitrospira</i> clade B were inhibited by the high ammonium concentrations released from the urine substrates. These results demonstrate the differential and niche responses of the three ammonia oxidising communities to N substrate additions and nitrification inhibitor treatments. Further research is needed to investigate the specificity of the two inhibitors on the different ammonia oxidising communities.