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Effects of Elevated CO2 and Soil Nitrogen on Seasonal Gas Exchange in Wheat
Brooks, T.J., Wall, G.W., Pinter Jr., P.J., Kimball, B.A., LaMorte, R.L., Leavitt, S.W., Matthias, A.D., Adamsen, F.J., Hunsaker, D.J. and Webber, A.N.  2000.  Acclimation response of spring wheat in a free-air CO2 enrichment (FACE) atmosphere with variable soil nitrogen regimes.  3. Canopy architecture and gas exchange.  Photosynthesis Research 66: 97-108.

What was done
Spring wheat (Triticum aestivum L. cv. Yecora Rojo) was grown for two seasons at atmospheric CO2 concentrations of 370 and 570 ppm in FACE plots located in Arizona, USA.  Additionally, at each CO2 concentration half of each experimental plot received high amounts of nitrogen, while the other half received low amounts.  Thus, the authors studied the interactive effects of elevated CO2 and soil nitrogen supply on the productivity of this important cereal species, focusing on data related to canopy architecture and gas exchange.

What was learned
Although plants receiving low nitrogen inputs to their soils experienced reduced seasonal carbon accumulation in both CO2 treatments, plants grown in the CO2-enriched plots accumulated 8 and 16% more carbon during the two growing seasons than plants exposed to ambient air under low and high soil nitrogen treatments, respectively.

On another note, leaves in the high soil nitrogen and CO2-enriched environments were more planar in their spatial distribution than leaves in the low soil nitrogen and ambient CO2 environments, which were more erect.  This change in canopy architecture from more planar to more erect foliage in going from higher to reduced atmospheric CO2 and soil nitrogen concentrations may help to reduce the negative effects of reduced resource availability on plant carbon accumulation.

What it means
As the CO2 content of the air rises, it is likely that spring wheat yields will also increase, due to enhanced season-long carbon accumulation in both low and high soil nitrogen environments.  Although much of this increase will likely result from reductions in photorespiration and increased carboxylation efficiency of the enzyme rubisco, it is also possible that an increasingly more planar distribution of foliage will contribute to the growing productivity of wheat.

Reviewed 23 January 2002