Differing responses to carbon dioxide enrichment by a dwarf and a normal-sized soybean cultivar may depend on sink capacity

Sicher, R., Bunce, J. and Matthews, B. 2010. Differing responses to carbon dioxide enrichment by a dwarf and a normal-sized soybean cultivar may depend on sink capacity. Can. J. Plant Sci. 90: 257-264. Responses to CO2 enrichment were determined for a dwarf (MiniMax) and a normal-sized (Fiskeby) soybean [Glycine max (L.) Merr.]. Plants were grown in growth chambers with ambient (36 Pa) or elevated (98 Pa) CO2 using a 2 x 2 x 2 factorial design. Harvests for Mini Max and Fiskeby were increased 6 and 26 d, respectively, by CO2 enrichment. At final maturity, mean biomass for Mini Max and Fiskeby was 53 and 197 g, respectively, in the ambient CO2 treatment and these values were 48 and 199% greater, respectively, in response to CO2 enrichment. Root development was constrained in Mini Max and, unlike Fiskeby, all of the biomass attributed to CO2 enrichment was in the shoot. Cultivar differences were not detected for CO2 assimilation rates, stomatal conductance or substomatal CO2 concentrations. Foliar sucrose was 43% greater (P < 0.05) in Mini Max than in Fiskeby. Pods per plant, total seed mass per plant, seed number per plant and seed oil content were greater for Fiskeby than Mini Max. Seeds of Fiskeby were 75% greater by mass than those of Mini Max. Seed mass of Fiskeby increased about 50% in response to CO2 enrichment, whereas Mini Max was unchanged. Root growth, seed size, seeds per pod and starch accumulation rates for Mini Max were unaffected by CO2 enrichment. The above findings suggested that growth of the dwarf genotype under elevated CO2 was sink limited.