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Seasonal Effects of Elevated CO2 on Winter Wheat
Dijkstra, P., Schapendonk, A.H.M.C., Groenwold, K., Jansen, M. and Van de Geijn, S.C.  1999.  Seasonal changes in the response of winter wheat to elevated atmospheric CO2 concentration grown in open-top chambers and field tracking enclosures.  Global Change Biology 5: 563-576.

What was done
The authors grew winter wheat (Triticum aestivum cv. Ritmo) in open-top chambers and field-tracking sun-lit climatized enclosures receiving atmospheric CO2 concentrations of ambient and ambient plus 350 ppm CO2 (elevated) for two years to study seasonal responses of this important cereal crop to elevated CO2.

What was learned
Elevated CO2 had little effect on canopy photosynthesis and biomass production early in the spring (January until April).  However, as the season progressed, and air temperature and solar irradiance rose, so too did the positive effects of elevated CO2 on these plant processes increase.  Canopy photosynthesis, for example, was enhanced in CO2-enriched wheat by 40% in late spring, although it ultimately dropped to 23% by the end of the growing season.  In addition, elevated CO2 increased final grain yield and total aboveground biomass by 19%.  Elevated CO2 also reduced rates of evapotranspiration across the entire season by 10 to 21%, which consequently contributed to water-use efficiencies in CO2 enriched plants that were 47 to 77% greater than those observed in ambiently-grown plants.

What it means
As the CO2 content of the air continues to rise, winter wheat should respond by exhibiting increases in canopy photosynthesis and biomass production, while simultaneously losing less water through each unit area of leaf surface.  Thus, winter wheat crops in a future high-CO2 world should produce significantly greater yields - and do it a more water-use efficient manner - than they do today.

Reviewed 6 February 2002