Grazing amplifies the stimulating effects of N addition on N2O emissions in a temperate meadow steppe

Nitrogen (N) addition typically increases nitrous oxide (N 2 O) emissions, but the magnitude of this effect depends on land use type and intensity. Grazing has an important influence on grassland N dynamics, but it is not clear to what extent grazing may interact with N addition in affecting grassland N 2 O emissions. We investigated the mechanisms underlying the individual and interactive effects of N addition and cattle grazing (control (CK), N addition (N), grazing (G), and N addition plus grazing (N + G) treatments) on N 2 O emissions in a temperate meadow steppe by measuring N 2 O fluxes, weather factors, vegetation parameters and soil properties from October 2017 to September 2018. The studied temperate meadow steppe was a source of N 2 O emissions during the experimental period. Approximately 80 % of the annual N 2 O emissions were released during the plant growing season. The highest N 2 O emission was detected in the N + G plots, which indicated the grazing treatment amplified the stimulating effects of N addition on N 2 O emissions. The results from structural equation model (SEM) suggested that N addition enhanced N 2 O emission through increases in NH 4 + -N concentration and soil potential net nitrification rate (N nitri ); grazing promoted N 2 O emissions by increasing substrate availability directly via excreta or indirectly through trampling-associated soil aggregate disruption and substrate release. N 2 O emissions increased most strongly with N addition and grazing due to the synergetic effects between animal trampling, animal excreta and available N on the processes of nitrification and denitrification. Overall, our results suggest that the interactive effects of grassland management and global change factors on N 2 O emissions need to be considered for the accurate assessment of grassland greenhouse gas emissions. • The studied temperate meadow steppe was a source of N 2 O emissions. • N addition and grazing did not change the seasonal distribution pattern of N 2 O emissions. • Grazing promoted N 2 O emissions through trampling and excretion. • Grazing amplified the stimulating effect of N addition on N 2 O emissions. • N 2 O fluxes were correlated with soil bulk density, inorganic N content and pH.