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

Author
item Sicher Jr, Richard
item Bunce, James
item Matthews, Benjamin - Ben

Submitted to: Canadian Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2009
Publication Date: 3/3/2010
Citation: Sicher Jr, R.C., Bunce, J.A., Matthews, B.F. 2010. Differing responses to carbon dioxide enrichment by a dwarf and a normal-sized soybean cultivar may depend on sink capacity. Canadian Journal of Plant Science. 90:257-264.

Interpretive Summary: Carbon dioxide concentrations in the atmosphere are increasing because of fossil fuel consumption and the destruction of forests. Because carbon dioxide is used for plant growth, changes in atmospheric levels of carbon dioxide can affect the economic yields of crop plants. Experiments studying the effects of elevated carbon dioxide on plant growth are usually performed in chambers or field enclosures and typically involve only a small number of plants. For obvious reasons it is difficult to predict large scale changes to agricultural systems based on results of small experiments performed in enclosures. The current study compared growth responses of a genetic dwarf to that of a full-sized soybean cultivar. Two to three times as many dwarf soybean plants could be grown in an enclosure when compared to the full-sized cultivar. Large differences in growth between the two lines were attributed to the very small root system of the dwarf soybean plants. The dwarf line also grew to maturity in less time than the full-sized soybean cultivars. The above findings showed that genetic dwarf plants could serve as a model system for studying the effects of carbon dioxide enrichment on growth and seed yields of soybean when plants were grown to maturity in environmental chambers. These finding should benefit agronomists, plant physiologists, ecologists and crop modelers interested in environmental change and future soybean production.

Technical Abstract: Growth and physiological characteristics of a superdwarf soybean genotype [Glycine max (L.) Merr. cv. MiniMax PI 643148] were compared with that of Fiskeby, a full-sized cultivar. Plants were grown in matching controlled environment chambers at 27° C and with either ambient (36 Pa) or elevated (98 Pa) CO2. Harvests at seed maturity for MiniMax and Fiskeby occurred 63 and 85 days after sowing, respectively, when plants were grown under ambient CO2 and these were increased 6 and 26 d, respectively, by CO2 enrichment. Total biomass for MiniMax 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. Biomass accumulation for Fiskeby differed significantly (P < 0.05) at each harvest in response to CO2 enrichment, whereas MiniMax differed on the first and final harvests. Root development was severely constrained in MiniMax and, unlike Fiskeby, all of the additional biomass attributed to CO2 enrichment was observed in the shoot. Cultivar differences were not detected for CO2 assimilation rates, stomatal conductance or for substomatal CO2 concentrations but the short-term stimulation of photosynthesis by elevated CO2 was larger in MiniMax than in Fiskeby. The photosynthetic capacity of both Fiskeby and MiniMax decreased 20 to 35% during growth in elevated CO2. Starch and glucose did not differ (P > 0.05) between cultivars but foliar sucrose levels were 43% greater (P < 0.05) in MiniMax than in Fiskeby. Harvest index was about 50% greater for MiniMax than for Fiskeby when averaged over CO2 treatments. The number of pods per plant, total seed mass per plant, seed number per plant and seed oil content were all greater for Fiskeby than for MiniMax and all of these parameters were concomitantly increased by CO2 enrichment. Individual seeds of Fiskeby were on average 75% greater by mass than those of MiniMax. Individual seed mass of Fiskeby increased about 50% in response to CO2 enrichment, whereas that of MiniMax was unchanged. Unlike oil content, seed protein concentrations did not differ among genotypes. The above results showed that a superdwarf soybean cultivar could be used successfully to study the responses of growth and photosynthesis to CO2 enrichment, although full-sized cultivars are recommended for studies performed exclusively during the vegetative growth phase.