Effects of elevated CO2 on model calcareous grasslands : community, species, and genotype level responses

We investigated the responses of model calcareous grassland communities to three CO2 concentrations: 330, 500, and 660 mu L L(-1). The communities were composed of six species, Bromus erectus Hudson, Festuca ovina L., Prunella vulgaris L., Prunella grandiflora (L.) Scholler, Hieracium pilosella L., and Trifolium repens L., that are native to the calcareous grasslands of Europe. Genotypic variation in CO2 response was studied in Bromus erectus and Festuca ovina. Plants were harvested after c. 126 days of growth. We found that: 1 At the community level, there were marginally significant (0.1 greater than or equal to P < 0.05) increases in leaf and litter dry weight with increasing CO2 concentration. 2 There were significant differences between species in CO2 response, including both negative and positive responses. Prunella vulgaris had a significant negative response; Hieracium pilosella and Festuca ovina had significant positive responses; Prunella grandiflora had a marginally significant positive response; and Bromus erectus and Trifolium repens did not have significant responses. 3 There was significant variation among genotypes in the response to elevated CO2 in Bromus erectus, but not in Festuca ovina. Based on the observed species- and genotype-level variation in CO2 response of calcareous grassland plants in this and other studies, we speculate that increasing atmospheric CO2 concentrations will alter community structure in calcareous grasslands.