Variation in growth rate and ecophysiology among 34 grassland and savanna species under contrasting N supply: a test of functional group differences.

•   We tested the hypothesis that biological trait-based plant functional groups provide sufficient differentiation of species to enable generalization about a variety of plant ecophysiological traits or responses to nitrogen (N). •   Seedlings of 34 North American grassland and savanna species, representing 5 functional groups, were grown in a glasshouse in an infertile soil with or without N fertilization. •   Forbs, C and C grasses, on average, had similar relative growth rates (RGR), followed in declining order by legumes and oaks, but RGR varied greatly among species within functional groups.