Genotype-specific effects of elevated CO 2 on fecundity in wild radish ( Raphanus raphanistrum )

Abstract

Rising atmospheric CO 2 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 CO 2 responses of wild species. We tested for heritable variation in CO 2 -dependent life history responses in a weedy, cosmopolitan annual, Raphanus raphanistrum . Progeny from five paternal families were grown at ambient and twice ambient CO 2 using outdoor open-top chambers (160 plants per CO 2 treatment). Elevated CO 2 stimulated net assimilation rates, especially in plants that had begun flowering. Across paternal families, elevated CO 2 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 CO 2 treatment: in three families there were no significant CO 2 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 CO 2 interaction, our results provide evidence for heritable responses to elevated CO 2 . In a subset of plants, we found that the magnitude of CO 2 effects on fecundity was also influenced by soil fertility.