GENOTYPE-SPECIFIC EFFECTS OF ELEVATED CO2 ON FECUNDITY IN WILD RADISH(RAPHANUS-RAPHANISTRUM)

Rising atmospheric CO2 may lead to natural selection for genotypes tha t exhibit greater fitness under these conditions. The potential for su ch evolutionary change will depend on the extent of within-population genetic variation in CO2 responses of wild species. We tested for heri table variation in CO2-dependent life history responses in a weedy, co smopolitan annual, Raphanus raphanistrum. Progeny from five paternal f amilies were grown at ambient and twice ambient CO2 using outdoor open -top chambers (160 plants per CO2 treatment). Elevated CO2 stimulated net assimilation rates, especially in plants that had begun flowering. Across paternal families, elevated CO2 led to significant increases i n flower and seed production (by 22% and 13% respectively), but no eff ect was seen on time to bolting, leaf area at bolting, fruit set, or n umber of seeds per fruit. Paternal families differed in their response to the CO2 treatment: in three families there were no significant CO2 effects, while in one family lifetime fecundity increased by > 50%. T hese genotype-specific effects altered fitness rankings among the five paternal families. Although we did not detect a significant genotype X CO2 interaction, our results provide evidence for heritable response s to elevated CO2. In a subset of plants, we found that the magnitude of CO2 effects on fecundity was also influenced by soil fertility.