Citation: Bunce, J.A. 2015. Elevated CO2 concentration effects on reproductive phenology and seed yield among soybean cultivars. Crop Science. 55:339-343.
The increase in seed yield caused by growth at elevated carbon dioxide concentrations varies greatly among varieties of soybean. Reasons for this variation are not known. This study found that the extension of the duration of vegetative growth caused by elevated carbon dioxide concentration was strongly linked to the increase in seed yield. This work will be of interest to scientists attempting to develop varieties of crops better adapted to rising atmospheric carbon dioxide concentrations.
Seed yield increases in soybeans caused by increased growth at elevated carbon dioxide concentrations primarily result from increased numbers of pods. However, reasons for differences among cultivars in the increases in pod number caused by elevated carbon dioxide are not clear. In experiments in controlled environment chambers cultivars varied in how much elevated carbon dioxide delayed the transition of the apical node of the main stem from vegetative to reproductive growth. The longer the delay in the transition, the more main stem and total nodes and pods were produced, increasing the relative stimulation of seed yield. A comparison of three indeterminate cultivars grown in free-air carbon dioxide enrichment systems in the field indicated that the time of the first open flower, and the rate of progression through reproductive stages was faster, slower, or unchanged by elevated carbon dioxide concentration in the three cultivars. However, independently from these effects on the rate of progression through the flowering stages, elevated carbon dioxide concentration also differentially affected the overall duration of vegetative growth, and the number of main stem and total nodes and pods produced. The extension of the duration of vegetative growth caused by elevated carbon dioxide was highly correlated with the relative seed yield increase in the field, as well as in the controlled environment chamber experiments.
CO2 Science explains the importance of soybean crops:
Soybean (Glycine max) is one of the top 15 crops grown worldwide. It is a highly prized legume appreciated for its many agricultural and industrial uses. Compared with other major staple food crops, it is exceptionally nutritious; it is high in protein content, calcium, thiamin, dietary fiber, iron, manganese, phosphorus, vitamin C, vitamin K, and several B vitamins. In the future, soybean production is expected to increase. Thus, there is much interest in learning about this important crop and how to increase its seed yield without expending additional costs and resources. And to this end, many scientists continue to study the impacts of rising atmospheric carbon dioxide (CO2) concentrations on soybeans.
In an important work that recently caught our attention, James Bunce -- a USDA researcher from the Crop System and Global Change Laboratory in Beltsville, Maryland, USA -- reports that seed yield increases have been observed by many scientists in soybean plants grown under elevated levels of atmospheric CO2. However, he notes that there are often large response differences among cultivars, the reasons for which "are not clear." In a search for answers, Bunce (2015) therefore set out to conduct his own study to investigate the impacts of elevated CO2 on soybean seed yield. More specifically, he grew three soybean cultivars (Fiskeby V, Ripley and Spencer) from seed to harvest in indoor controlled environment chambers at either 380 or 560 ppm CO2, as well as three cultivars (Mandarin, Holt and Spencer) in an outdoorenvironment at either 451 or 659 ppm CO2 using free-air CO2 enrichment (FACE) technology. Measurements were made during the course of the growing season in an attempt to determine the cause of seed yield variation among cultivars at enhanced levels of atmospheric CO2.Read more at CO2 Science