EFFECTS OF ELEVATED CO2 ON MODEL CALCAREOUS GRASSLANDS - COMMUNITY, SPECIES, AND GENOTYPE LEVEL RESPONSES

We investigated the responses of model calcareous grassland communitie s to three CO2 concentrations: 330, 500, and 660 mu L L(-1). The commu nities were composed of six species, Bromus erectus Hudson, Festuca ov ina L., Prunella vulgaris L., Prunella grandiflora (L.) Scholler, Hier acium pilosella L., and Trifolium repens L., that are native to the ca lcareous grasslands of Europe. Genotypic variation in CO2 response was studied in Bromus erectus and Festuca ovina. Plants were harvested af ter c. 126 days of growth. We found that: 1 At the community level, th ere were marginally significant (0.1 greater than or equal to P > 0.05 ) increases in leaf and litter dry weight with increasing CO2 concentr ation. 2 There were significant differences between species in CO2 res ponse, including both negative and positive responses. Prunella vulgar is had a significant negative response; Hieracium pilosella and Festuc a ovina had significant positive responses; Prunella grandiflora had a marginally significant positive response; and Bromus erectus and Trif olium repens did not have significant responses. 3 There was significa nt 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 plan ts in this and other studies, we speculate that increasing atmospheric CO2 concentrations will alter community structure in calcareous grass lands.