SUMMARY

Plant species native to CO2 springs have evolved along gradients of naturally elevated atmospheric CO2 concentrations that differ as much as predicted for anthropogenic increases in CO2 over the next 100-200 years. This study characterized differences in gro wth and dry matter partitioning under controlled conditions in two species, Agrostis canina L. spp. montelucci (Selvi, 1994) and Plantago major L., adapted to contrasting atmospheric CO2 concentrations. When plants were grown at twice the present CO2 level there was a pronounced increase in biomass production, which was largely due to an initial stimulation in relative growth rate. In Agrostis canina, CO2 enrichment caused an increase in the relative partitioning of dry matter to the root, but effects were less pronounced in Plantago major. Specific leaf area was reduced by elevated CO2 in both species. Plants adapted to growth at high CO2 produced greater biomass and exhibited higher initial RGRs than plants adapted to lower CO2 concentrations, and in the case of Agrostis canina these differences were maintained at ambient CO2. Differences in original seed weight between populations were small (<10% for Agrostis and < 20% for Plantago). A positive correlation was, however, found between seed weight and the long-term atmospheric CO2 concentration at the site of collection and larger seeds were associated with higher initial plant RGRs under CO2 enriched conditions.