What was done
The authors collected 9 to 14 genotypes for each of 12 native grassland species from two permanent meadows near Zurich (Switzerland) and transplanted them into artificial gaps created within well-fertilized swards of Lolium perenne growing within FACE arrays receiving 350 and 700 ppm CO2 to determine inter- and intraspecific species growth responses to elevated CO2 by harvesting aboveground biomass several times over a three-year period.

What was learned
The doubled CO2 content of the air generally increased aboveground biomass in all 12 species, with greater growth responses being reported in the spring than in the summer/autumn harvests.  The CO2-induced biomass increases varied with plant type and were clearly greatest for legume species, followed by non-legume dicotyledonous species and lastly the monocotyledonous grasses.  However, there were no significant differences in CO2 responsiveness within genotypes for any of the 12 species, suggesting that rapid evolutionary adaptations in species-specific responses are not likely to occur.

What it means
As the CO2 content of the air continues to rise, the differing responsiveness of different plant species to elevated CO2 may alter plant composition in fertile grasslands.  In particular, nitrogen-fixing species may perform better than other plants, and dicots may fare better than monocot grasses.  These results must be taken with caution, however, as temporal differences in responsiveness to elevated CO2 among species depends on numerous competitive and cooperative interactions that are not well understood.