Genotype x elevated CO2 interaction and allocation in calcareous grasslandspecies

Biomass of genotypes of Carex flacca and Bromus erectus under CO2 enrichmen t was measured to test for 'winners' and 'losers' within the populations. A llocation was studied to identify reasons for varying biomass responses of the genotypes. In a first experiment, genotypes of both species were grown separately and mown five times. In a second experiment, introducing species interaction, s pecies were grown together (using nine genotypes of each) and harvested des tructively during that time. The first experiment showed that growth stimulation across harvests (Bromus +15%; Carex +11%) and genotype X CO2 treatment interactions in single harv ests was significant, but repeated measures ANOVA was not (Carex) or only m arginally significant (Bromus). Destructive harvests in the competition exp eriment indicated a significant growth stimulation (Bromus +28%, Carex +35% ), but no CO2 x genotype interaction was found. Similarly, ANOVA of dry mat ter allocation never indicated a significant CO2 x genotype interaction. The lack of a sustained CO2 x genotype interaction in isolated and competit ive growth conditions with good moisture supply suggests, that if there is such an interaction, it must be very small. (C) New Phytologist (2001).