A greenhouse experiment was conducted with five Elymus grass species: Elymus dahuricus Turcz., Elymus cylindricus Franchet, Elymus breviaristatus Keng f., Elymus nutans Griseb., and Elymus sibiricus L., measuring N2O emissions from sheep urine-affected soil, and a biological nitrification inhibition (BNI) assay was performed on root exudates of these five species. The abundances of amoA gene of ammonia-oxidizing bacteria and archaea and nirK and nirS denitrification genes were measured by quantitative polymerase chain reaction. The mean total emissions over 6 weeks varied significantly among the Elymus species and ranged from 0.34 to 0.94 kg N2O-N·ha−1 in the urine treatment. The highest emissions were observed from Elymus breviaristatus while the lowest emissions were observed in Elymus sibiricus. All the Elymus grass species were capable of exuding BNI compounds and the highest BNI capacity was observed in Elymus sibiricus. The nirS gene abundance response to urine addition was significantly greater than other genes and varied significantly depending on Elymus species. The BNI % and nirS gene abundance were negatively and positively, respectively, related to total N2O-N emissions during the first 2 weeks after urine addition when emissions were apparent.