Submitted to: Australian Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 22, 2000
Publication Date: N/A
Interpretive Summary: Carbon dioxide is the sole source of carbon needed for plant growth. Many plants show increased growth as carbon dioxide in the atmosphere increases. However the relative response of growth and seed yield to increasing carbon dioxide varies significantly between and within plant species. This variation may provide opportunities for physiologists and breeders to select for given varieties which exploit rising carbon dioxide in order to maximize seed yield. To address this issue, we grew two contrasting varieties of soybean (Spencer and Ripley) in the field for a two-year period at current (370 ppm) and future (690 ppm)levels of carbon dioxide. For both years, Spencer significantly outperformed Ripley (60% vs. 35% increase in seed yield at future carbon dioxide levels). This increase was related to the ability of Spencer to form axillary branches with additional seed pods. Data from this experiment suggest that variation in the response of soybean to rising carbon dioxide levels could be used to choos soybean cultivars which would convert additional atmospheric carbon dioxide into enhanced seed yield.
Technical Abstract: Although genotypic differences among soybean cultivars in their response to future carbon dioxide have been observed in the glasshouse, it is unclear if similar responses would occur among cultivars when grown under field conditions at normal stand densities. To determine variation in the sensitivity of soybean growth and seed yield to CO2, we grew two contrasting cultivars of the same maturity group, Ripley (semi-dwarf, determinate) and Spencer (standard, indeterminate) to reproductive maturity at ambient and elevated (300 ppm above ambient) CO2 partial pressures for two field seasons. Spencer had been previously selected in glasshouse trials as responsive to increased CO2. Significant cultivar by CO2 interaction was observed for both vegetative biomass and seed yield with Spencer demonstrating a consistently greater yield enhancement at elevated CO2 than Ripley (60% vs. 35%, respectively). Differences in CO2 sensitivity between cultivars were not evident in measurements of single leaf photosynthesis taken during anthesis, early or late pod-fill. Analysis of reproductive characteristics indicated that the sensitivity of the yield response to CO2 in Spencer was associated with the ability to form additional seed on axillary branches in response to elevated CO2. Data from this experiment suggest that screening of soybean germplasm at the glasshouse level, when combined with field trials, may be an effective strategy to begin selecting soybean lines which will maximize yield in a future, higher CO2 environment.