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Effects of Increasing Atmospheric CO2 Concentration and Temperature on Soybean Seed Quality
Reference
Thomas, J.M.G., Boote, K.J., Allen Jr., L.H., Gallo-Meagher, M. and Davis, J.M.  2003.  Elevated temperature and carbon dioxide effects on soybean seed composition and transcript abundance.  Crop Science 43: 1548-1557.

Background
The authors say "the unique chemical composition of soybean has made it one of the most valuable agronomic crops worldwide," noting that "oil and protein comprise ~20 and 40%, respectively, of the dry weight of soybean seed."

What was done
Soybean (Glycine max (L.) Merr. cv. 'Bragg') plants were grown to maturity in sunlit controlled-environment chambers under sinusoidally-varying day/night-max/min temperatures of 28/18, 32/22, 36/26, 40/30 and 44/34°C and at two levels of atmospheric CO2 concentration (350 and 700 ppm), after which the harvested seeds were analyzed for a number of different quality parameters.

What was learned
It was determined that the effect of temperature on seed composition and gene expression was "pronounced," in the words of the authors, but that "there was no effect of CO2."  In this regard, however, they note that "Heagle et al. (1998) observed a positive significant effect of CO2 enrichment on soybean seed oil and oleic acid concentration," the latter of which parameters the current study additionally found to increase with rising temperature all the way from 28/18 to 44/34°C.

Among other temperature effects observed, it was found that "32/22°C is optimum for producing the highest oil concentration in soybean seed," and that "the degree of fatty acid saturation in soybean oil was significantly increased by increasing temperature."  Also, crude protein concentration increased with temperature to 40/30°C.

What it means
The authors note that "the intrinsic value of soybean seed is in its supply of essential fatty acids and amino acids in the oil and protein, respectively."  Hence, we must conclude that the temperature-driven changes they identified in these parameters, as well as the CO2 effect observed by Heagle et al., bode well for the future production of this important crop and its value to society in a CO2-enriched and warming world.  Thomas et al. do note, however, that "temperatures during the soybean-growing season in the southern USA are at, or slightly higher than, 32/22°C," and that warming could negatively impact the soybean oil industry in this region.  For the world as a whole, however, warming would be a positive development for soybean production; while in the southern United States, shifts in planting zones could readily accommodate changing weather patterns associated with this phenomenon.

Reference
Heagle, A.S., Miller, J.E. and Pursley, W.A.  1998.  Influence of ozone stress on soybean response to carbon dioxide enrichment: III.  Yield and seed quality.  Crop Science 38: 128-134.


Reviewed 22 October 2003