LAUSR

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 N 2 O 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 N 2 O-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 N 2 O-N emissions during the first 2 weeks after urine addition when emissions were apparent.