INTERSPECIFIC AND INTRASPECIFIC VARIABILITY IN THE RESPONSE OF GRASSES AND LEGUMES TO FREE-AIR CO2 ENRICHMENT

Nine to fourteen genotypes of seven grass and two legume species from permanent grassland were grown at two levels of atmospheric CO2 concen tration in gaps of established Lolium perenne swards in a Free Air Car bon dioxide Enrichment (FACE) experiment. Cumulative biomass of indivi dual plants was determined for two growing seasons. In the first year, elevated CO2 increased biomass production in all species. The CO2-ind uced increase in the biomass of Trifolium repens and I: pratense (159% ) was much greater than the increase in the grass species (27%). In th e second year the response to elevated CO2 was weaker in gasses (2%, n s) and legumes (73%). However, interspecific differences in the respon se to CO2 remained significant. Interspecific differences in the respo nse to elevated CO2 occurred between the two functional groups of gras ses and legumes, while within these groups no significant interspecifi c differences were found. In contrast to the interspecific variability in the response to CO2, no significant intraspecific variability in t he response to CO2 was detected. Our results suggest that significant interspecific differences in the response to CO2, occur. Intraspecific differences in the response to elevated CO2 were, however, not detect ed. Thus, it seems unlikely that evolutionary adaptation of the specie s' response to elevated CO2 will level out the inter specific differen ces in the response to CO2.