Genotype-specific effects of elevated CO₂ on fecundity in wild radish (Raphanus raphanistrum)

Rising atmospheric CO₂ may lead to natural selection for genotypes that exhibit greater fitness under these conditions. The potential for such evolutionary change will depend on the extent of within-population genetic variation in CO₂ responses of wild species. We tested for heritable variation in CO₂-dependent life history responses in a weedy, cosmopolitan annual, Raphanus raphanistrum. Progeny from five paternal families 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 in flower and seed production (by 22% and 13% respectively), but no effect was seen on time to bolting, leaf area at bolting, fruit set, or number 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%. These 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 responses to elevated CO₂. In a subset of plants, we found that the magnitude of CO₂ effects on fecundity was also influenced by soil fertility.