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Seedling Response to Elevated CO2 in Five Epigeal Species

Evidence from numerous sources indicates that atmospheric CO2 concentration has increased over the last 200 yr and will continue to increase in the foreseeable future. Much research is directed toward predicting the effects of this change on terrestrial vegetation. We quantified the effects of elevated CO2 (700 &mgr;L L−1) on the seedling growth characteristics of five C3 species. These species all had epigeal germination morphology but differed by a factor of 20 in seed mass. The species and their respective seed‐mass ranges were as follows: bagpod sesbania (Sesbania vesicaria), 0.23–0.26 g; cotton (Gossypium hirsutum var. Coker 317), 0.12–0.13 g; mesquite (Prosopis glandulosa), 0.041–0.048 g; cucumber (Cucumis sativus L. cv. Straight‐8), 0.026–0.030 g; and hemp sesbania (Sesbania exaltata), 0.012–0.013 g. We measured increased total biomass in the elevated CO2 environment for all species within 3 d of emergence. This rapid response contrasts with published reports that more time was required for a detectable response of seedlings to elevated CO2. Growth analyses indicated that no single growth parameter predicted the responses of these species to elevated CO2. However, maximum area of cotyledons was a better predictor of total biomass (at day 16) than was initial (day 0) seedling mass. Our data indicate that future increases in atmospheric CO2 will greatly improve the competitive ability of C3 epigeal species during the earliest growth stage in which cotyledons are still expanding.