Do species and functional groups differ in acquisition and use of C, N and water 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 change, the responses to CO 2 concentration and N availability of grassland species 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 field monocultures under ambient or elevated (560 μmol mol -1) CO 2 using free-air CO 2 enrichment (FACE), in low N (unamended field soil) or high N (field soil +4 g N m -2 years -1) treatments. "¢ There were no CO 2 × N interactions. Functional groups responded differently to CO 2 and N in terms of biomass, tissue N concentration and soil solution N. Under elevated CO 2, forbs, legumes and C 3 grasses increased total biomass by 31%, 18%, and 9%, respectively, whereas biomass was reduced in C 4-grass monocultures. Two of the four legume species increased biomass and total plant N pools under elevated CO 2, probably due to stimulated N-fixation. Only one species markedly shifted the proportional distribution of below- vs aboveground biomass in response to CO 2 or N. "¢ Although functional groups varied in responses to CO 2 and N, there was also substantial variation in responses among species within groups. These results suggest that current trait-based functional classifications might be useful, but not sufficient, for understanding plant and ecosystem responses to elevated CO 2 and N availability.