摘要：Understanding how the growth of two key native grass species of the Northern Great Plains （Western wheatgrass and blue grama） may be affected under drought and nitrogen deficiency is essential for future management of these grasslands. The random complete block experimental design greenhouse study examined the effects of water and N addition on above-ground and below-ground harvested biomass of C3 （Western wheatgrass, WWG） and C4 （blue grama, BG） grass species for the purpose of gaining better understanding of drought responses for these two species. Compared with well-watered treatment （field capacity）, two water limited treatments （70% and 85% field capacity） decreased plant above- and below-ground biomass （WWG and BG）. For two N treatments （no N added, addition of 100 mg N kg^-1soil）, addition of N significantly improved plant above- and below-ground biomass of WWG and BG under water field capacity. Both above- and below-ground biomass of the two grass species increased linearly with increasing water supplied, but above- and below-ground biomass of WWG was always lower than BG for the same treatments （water or N addition）. The results demonstrated that BG seedlings had better adaptation than WWG to deal with the imposed drought or N deficient conditions.