Abstract:Aims We conducted a field manipulation experiment to examine the underpinning mechanisms of variation in plant leaf functional traits along a nitrogen addition gradient in a mature typical steppe ecosystem in Inner Mongolia. Methods We selected six dominant and sub-dominant plant species for study: Leymus chinensis, Achnatherum sibiricum, Agropyron cristatum, Stipa grandis, Cleistogenes squarrosa and Carex korshinskyi. Together, they account for >90% of the total community aboveground biomass. We examined the effects of N addition on specific leaf area (SLA), leaf N content, total chlorophyll content, and chlorophyll a/b ratio. Important findings Nitrogen addition lessened the N limitation while strengthening light competition among co-existing plant species. Plant species differed significantly in their responses to increased N addition rates. Leymus chinensis showed high plasticity in SLA, leaf N, and total chlorophyll content. Its area-based leaf N content increased linearly with N addition rate. Achnatherum sibiricum showed the highest plasticity in SLA and high mass-based leaf N and chlorophyll content to N enrichment, whereas its area-based leaf N content was relative stable. Compared to L. chinensis and A. sibiricum, A. cristatum had low plasticity in the three leaf functional traits investigated. Both S. grandis and C. korshinskyi illustrated low plasticity in SLA along with low SLA of S. grandis and short stature of C. korshinskyi,leading to reduced light competitive ability of the two species under N enrichment. Cleistogenes squarrosa had the highest SLA among the six species and a relatively high plasticity in mass-based leaf chlorophyll and N contents. The chlorophyll a/b ratio of C. squarrosa decreased significantly under N treatment, indicating declining light availability.