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Agriculture (Species -- Wheat) -- Summary
Nearly all crops respond to increases in the air's CO2 content by displaying enhanced rates of photosynthesis and biomass production.  Does the same hold true of Triticum aestivum, better known to most of us as wheat?  Let's see what some of the atmospheric CO2 enrichment studies of the last few years have revealed about the subject.

In a FACE study conducted in Arizona, USA, wheat plants grown at 570 ppm CO2 exhibited enhanced rates of photosynthesis that led to approximately 8 and 16% more seasonal carbon uptake under low and high soil nitrogen conditions, respectively (Brooks et al., 2000).  Similarly, Dijkstra et al. (1999) report that twice-ambient atmospheric CO2 concentrations stimulated rates of photosynthesis by 20 to 50%, depending upon the prevailing irradiance and temperature.

Because elevated CO2 stimulates rates of photosynthesis in wheat, it should also increase biomass and grain yield.  And it does.  In the Arizona FACE study, for example, the extra 200 ppm of CO2 increased grain yields by 17 and 14% in water-stressed and well-watered plants, respectively (Li et al., 2000).  Schutz and Fangmeier (2001), however, reported even larger CO2-induced yield stimulations in their open-top chamber experiment in response to a 300-ppm increase in the atmosphere's CO2 concentration: 54% vs. 40% for water-stressed and well-watered plants, respectively.  Likewise, Masle (2000) reported that a 550-ppm increase in the air's CO2 concentration increased the plant dry weight of wheat by 50 to 90%.  In addition, twice-ambient CO2 concentrations have been shown to increase the grain yield of wheat by 13% (Monje and Bugbee, 1998) and by 10-20% (Pleijel et al., 2000).  Moreover, various crop growth models applied to different climate change scenarios have predicted significant CO2-induced wheat yield increases in Bulgaria (Alexandrov and Hoogenboom, 2000) and Australia (Reyenga et al., 2001).  A doubling of the atmospheric CO2 concentration even increased the grain yield of wheat plants infected with a rust-causing fungus by 28 and 42% under conditions of ambient and elevated ozone concentrations (Tiedemann and Firsching, 2000).

On another note, Wall (2001) reported that wheat plants grown at 550 ppm CO2 in the Arizona FACE experiment maintained more positive (less stressful) leaf water potentials than plants grown in air containing 370 ppm CO2.  Using this same experimental setup, Hunsaker et al. (2000) further noted that the water-use efficiency of CO2-enriched plants was 10 and 20% greater than that displayed by their ambiently-grown counterparts under low and high soil nitrogen regimes, respectively.  In addition, Dijkstra et al. (1999) reported that the CO2-induced increase in the water-use efficiency of wheat in their open-top chamber experiment was as high as 77%.

In summary, as the air's CO2 content continues to rise, wheat plants should display increasingly greater rates of photosynthesis and biomass production, which should lead to ever greater grain yields in this important cereal crop, even under conditions of low soil moisture or poor soil fertility.

For more information on wheat growth responses to atmospheric CO2 enrichment see Plant Growth Data: Wheat (dry weight, photosynthesis).

References
Alexandrov, V.A. and Hoogenboom, G.  2000.  The impact of climate variability and change on crop yield in Bulgaria.  Agricultural and Forest Meteorology 104: 315-327.

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.

Dijkstra, P., Schapendonk, A.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.

Hunsaker, D.J., Kimball. B.A., Pinter, P.J., Jr., Wall, G.W., LaMorte, R.L., Adamsen, F.J., Leavitt, S.W., Thompson, T.L., Matthias, A.D. and Brooks, T.J.  2000.  CO2 enrichment and soil nitrogen effects on wheat evapotranspiration and water use efficiency.  Agricultural and Forest Meteorology 104: 85-105.

Li, A.-G., Hou, Y.-S., Wall, G.W., Trent, A., Kimball, B.A. and Pinter Jr., P.J.  2000.  Free-air CO2 enrichment and drought stress effects on grain filling rate and duration in spring wheat.  Crop Science 40: 1263-1270.

Masle, J.  2000.  The effects of elevated CO2 concentrations on cell division rates, growth patterns, and blade anatomy in young wheat plants are modulated by factors related to leaf position, vernalization, and genotype.  Plant Physiology 122: 1399-1415.

Monje, O. and Bugbee, B.  1998.  Adaptation to high CO2 concentration in an optimal environment: radiation capture, canopy quantum yield and carbon use efficiency.  Plant, Cell and Environment 21: 315-324.

Pleijel, H., Gelang, J., Sild, E., Danielsson, H., Younis, S., Karlsson, P.-E., Wallin, G., Skarby, L. and Sellden, G.  2000.  Effects of elevated carbon dioxide, ozone and water availability on spring wheat growth and yield.  Physiologia Plantarum 108: 61-70.

Reyenga, P.J., Howden, S.M., Meinke, H. and Hall, W.B.  2001.  Global change impacts on wheat production along an environmental gradient in south Australia.  Environmental International 27: 195-200.

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.

Tiedemann, A.V. and Firsching, K.H.  2000.  Interactive effects of elevated ozone and carbon dioxide on growth and yield of leaf rust-infected versus non-infected wheat.  Environmental Pollution 108: 357-363.

Wall, G.W.  2001.  Elevated atmospheric CO2 alleviates drought stress in wheat.  Agriculture, Ecosystems and Environment 87: 261-271.