Abstract: We assessed the effects of utilization mode (grazing and exclosure) and short-termnitrogen addition (0, 5, 10, 20 g·m^-2) on species diversity and functional diversity in grazing grassland and enclosed grassland in Horqin sandy land. For enclosed grassland, the vegetation height, density, coverage and biomass increased and species richness and dominance decreased with increasing nitrogen additions. The increasing nitrogen additions significantly decreased the indices of root traits for enclosed grassland, but had no effects on functional diversity except Rao index in 20 g·m^-2 nitrogen addition treatment. Grazing had greater effects on vegetation status and diversity of grassland than nitrogen addition. CWM of specific root length significantly increased with the increasing nitrogen additions. The interaction of exclosure and low nitrogen additions could stimulate vegetation restoration and plant diversity. In contrast, higher nitrogen additions would reduce plant diversity and ecosystem stability. Biomass was negatively correlated with plant diversity indices. Vegetation and species diversity were more sensitive than plant traits and functional diversity to short-term exclosure and nitrogen addition. Plant root traits showed strong responses to management measures, which suggested that functional diversity should be further studied to clarify the long term effects of grassland management.

Key words: shade tolerance, light availability., plasticity, forest plant, light, ontogeny