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 fo reseeable future. Much research is directed toward predicting the effects o f this change on terrestrial vegetation. We quantified the effects of eleva ted CO2 (700 muL L-1) on the seedling growth characteristics of five C-3 sp ecies. These species all had epigeal germination morphology but differed by a factor of 20 in seed mass. The species and their respective seed-mass ra nges were as follows: bagpod sesbania (Sesbania vesicaria), 0.23-0.26 g; co tton (Gossypium hirsutum var. Coker 317), 0.12-0.13 g; mesquite (Prosopis g landulosa), 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 measu red increased total biomass in the elevated CO2 environment for all species within 3 d of emergence. This rapid response contrasts with published repo rts that more time was required for a detectable response of seedlings to e levated CO2. Growth. analyses indicated that no single growth parameter pre dicted the responses of these species to elevated CO2. However, maximum are a of cotyledons was a better predictor of total biomass (at day 16) than wa s initial (day 0) seedling mass. Our data indicate that future increases in atmospheric CO2 will greatly improve the competitive ability of C-3 epigea l species during the earliest growth stage in which cotyledons are still ex panding.