Nitrification inhibitors effectively target N(2)O‐producing Nitrosospira spp. in tropical soil

The nitrification inhibitors (NIs) 3,4‐dimethylpyrazole (DMPP) and dicyandiamide (DCD) can effectively reduce N(2)O emissions; however, which species are targeted and the effect of these NIs on the microbial nitrifier community is still unclear. Here, we identified the ammonia oxidizing bacteria (AOB) species linked to N(2)O emissions and evaluated the effects of urea and urea with DCD and DMPP on the nitrifying community in a 258 day field experiment under sugarcane. Using an amoA AOB amplicon sequencing approach and mining a previous dataset of 16S rRNA sequences, we characterized the most likely N(2)O‐producing AOB as a Nitrosospira spp. and identified Nitrosospira (AOB), Nitrososphaera (archaeal ammonia oxidizer) and Nitrospira (nitrite‐oxidizer) as the most abundant, present nitrifiers. The fertilizer treatments had no effect on the alpha and beta diversities of the AOB communities. Interestingly, we found three clusters of co‐varying variables with nitrifier operational taxonomic units (OTUs): the N(2)O‐producing AOB Nitrosospira with N(2)O, NO(3) (−), NH(4) (+), water‐filled pore space (WFPS) and pH; AOA Nitrososphaera with NO(3) (−), NH(4) (+) and pH; and AOA Nitrososphaera and NOB Nitrospira with NH(4) (+), which suggests different drivers. These results support the co‐occurrence of non‐N(2)O‐producing Nitrososphaera and Nitrospira in the unfertilized soils and the promotion of N(2)O‐producing Nitrosospira under urea fertilization. Further, we suggest that DMPP is a more effective NI than DCD in tropical soil under sugarcane.