Do species and functional groups differ in acquisition and use of C, N andwater under varying atmospheric CO2 and N availability regimes? A field test with 16 grassland species

To evaluate whether functional groups have a similar response to global cha nge, the responses to CO2 concentration and N availability of grassland spe cies from several functional groups are reported here. Sixteen perennial grassland species from four trait-based functional groups (C-3 grasses, C-4 grasses, non-leguminous forbs, legumes) were grown in fi eld monocultures under ambient or elevated (560 mu mol mol(-1)) CO2 using f ree-air CO2 enrichment (FACE), in low N (unamended field soil) or high N (f ield soil +4 g N m(-2) years(-1)) treatments. There were no CO2 x N interactions. Functional groups responded differently to CO2 and N in terms of biomass, tissue N concentration and soil solution N. Under elevated CO2, forbs, legumes and C-3 grasses increased total biom ass by 31%, 18%, and 9%, respectively, whereas biomass was reduced in C-4-g rass monocultures. Two of the four legume species increased biomass and tot al plant N pools under elevated CO2, probably due to stimulated N-fixation. Only one species markedly shifted the proportional distribution of below-v s aboveground biomass in response to CO2 or N. Although functional groups varied in responses to CO2 and N, there was also substantial variation in responses among species within groups. These resu lts suggest that current trait-based functional classifications might be us eful, but not sufficient, for understanding plant and ecosystem responses t o elevated CO2 and N availability.