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Elevated CO2 and Soybeans: Ground- vs. Container-Grown Plants
Fiscus, E.L., Booker, F.L., Dubois, J.-J. B., Rufty, T.W., Burton, J.W. and Pursley, W.A. 2007. Carbon dioxide enhancement effects in container- versus ground-grown soybean at equal planting densities. Crop Science 47: 2486-2494.

What was done
The authors grew well watered and fertilized soybean (Glycine max (L.) Merr. cv. Essex) plants from seed to maturity for one full growing season out-of-doors near Raleigh, North Carolina (USA) within open-top chambers, either rooted in the ground or in 21-L pots (one plant per pot) at equal plant densities per unit ground area, while exposing the plants to charcoal-filtered air maintained at CO2 concentrations of either 370 or 700 ppm.

What was learned
Although seed yields in the container-grown plants were about 17% less than those of the plants rooted directly in the ground, the CO2-induced enhancement ratios of both sets of plants were not significantly different from each other, averaging approximately 20%. In addition, the six researchers say "there was a small (3-4%) but highly significant increase in the seed oil concentration due to elevated CO2," and that this increase was experienced "in both rooting environments.

What it means
Fiscus et al. conclude that CO2-induced growth enhancement ratios are "relatively indifferent to baseline growth and yield," having demonstrated that when plant densities and between-plant spacings are identical, equivalent CO2-induced growth enhancement ratios may be obtained from both ground-rooted and container-rooted plants.

On another note, they say that "the 3 to 4% increase in oil per seed would amount to a very substantial increase in oil production of a regional, national, or international scale." For the year 2005, for example, they calculate that "an increase of 3.5% of seed oil concentration could result in an additional 2.9 Tg of seed oil in a future climate with CO2 concentrations well above current ambient levels," and that "considering commonly observed CO2 enrichment ratios, that number could rise to more than 20 Tg.

Reviewed 16 April 2008