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Effects of Elevated CO2, Soil Water Content, and Soil Fertility on Wheat
Schutz, M. and Fangmeier, A.  2001.  Growth and yield responses of spring wheat (Triticum aestivum L. cv. Minaret) to elevated CO2 and water limitation.  Environmental Pollution 114: 187-194.

What was done
The authors grew spring wheat (Triticum aestivum L. cv. Minaret) for an entire season in pots placed within open-top chambers receiving atmospheric CO2 concentrations of 367 and 650 ppm.  Within each CO2 treatment, plants were grown in two different soils, one of which was lower in fertility than the other.  In addition, plants were further subjected to a well-watered or water-stressed irrigation regime.  Thus, the authors studied the single and combined effects of elevated CO2, soil type and soil moisture on growth and yield in this variety of the world's most important food crop.

What was learned
Alone, each of the three primary variables significantly affected plant growth and yield in this species.  Elevated CO2, for example, increased shoot biomass by 43%, as did (surprisingly) the soil with the low fertility, increasing shoot biomass by 30%.  In contrast, water stress reduced this parameter by 40%.  On a similar note, atmospheric CO2 enrichment and low soil fertility stimulated grain yield by 46 and 39%, respectively, while water stress decreased it by 45%.

As far as interactive trends are concerned, there was a tendency for elevated CO2 to partially alleviate the growth and yield reductions caused by water stress.  Total shoot biomass and grain yield, for example, were reduced due to water stress by 47 and 49%, respectively, at ambient CO2 concentrations.  Under elevated CO2 concentrations, however, these same plant parameters were only reduced by 36 and 43%, respectively.  Interestingly, on a percentage basis, elevated CO2 stimulated yield more under water-stressed, as opposed to well-watered, conditions (57 vs. 40%, respectively).

What it means
As the air's CO2 content continues to rise, it will likely cause significant increases in the growth and yield of spring wheat, regardless of soil fertility and moisture conditions.  Thus, we can look forward to increases in grain production without increasing the amount of land being farmed, which will benefit both mankind and nature alike.