Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 2001
Publication Date: N/A
Interpretive Summary: Atmospheric carbon dioxide provides the carbon for all living things. As carbon dioxide continues to increase in the atmosphere, can we select within a given agricultural plant, such as soybean, for varieties which show the strongest yield response? If we can identify these varieties and their characteristics, this would allow a substantial increase in soybean productivity with little environmental cost. The study described herein attempts to do so by examining twelve different soybean cultivars (those which are the ancestral varieties for all modern soybean production) at current (ambient) and future (elevated) levels of carbon dioxide in order to quantify and utilize variability in the response of seed yield to increasing carbon dioxide. The study found that some cultivars of soybean increased their current yields by as much as 80% as carbon dioxide increased. For those soybean varieties showing the largest increase in seed yield, the increases were associated with changes in branching patterns, pod production and an increase in individual pod and seed weight at the higher carbon dioxide concentration. Data from the study indicate that these observed changes in reproduction could be used to establish a set of selection criteria which could be useful to plant breeders in optimizing the seed yield response of soybean as atmospheric carbon dioxide increases.
Technical Abstract: To determine the physiological or morphological basis for the vegetative and seed yield response of soybean to increasing atmospheric carbon dioxide, and to quantify the range of response of seed yield, eleven ancestral and one modern cultivar differing in determinacy, maturity group and growth habit were grown to reproductive maturity at two CO2 partial pressures, 40 Pa (ambient) and 71 Pa (elevated) in temperature controlled glasshouses at the Climate Stress Laboratory twice during Spring through Fall of 1998. Significant intraspecific variation in the responses of both vegetative growth and seed yield to elevated CO2 were observed between cultivars. Overall, elevated CO2 increased total biomass by 0 to 76%, with an average of 43% at the end of the vegetative stage, while average seed yield increased by only 31% with a range of 0 to 80%. The degree of intraspecific variation was independent of differences in the response of single leaf photosynthesis among cultivars at elevated CO2. Vegetative growth responses (e.g., leaf area, leaf weight) or differences in the partitioning of vegetative mass among organs (e.g. root/shoot) were also independent of seed yield variation. Specific reproductive characteristics which increased yield at elevated CO2 were lateral branching and a subsequent increase in pod numbers, as well as an increase in individual pod and seed weight. These data indicate that variation in carbon partitioning to and among reproductive structures could be used to establish a set of selection criteria which would utilize increasing atmospheric CO2 to maximize future seed yield in soybean.