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Title: PRODUCTIVITY AND WATER USE OF WHEAT UNDER FREE-AIR CO2 ENRICHMENT

Author
item Kimball, Bruce
item Pinter Jr, Paul
item GARCIA, RICHARD - LICOR, INC
item La Morte, Robert
item Wall, Gerard - Gary
item Hunsaker, Douglas - Doug

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: The CO2 concentration of the atmosphere is expected to double during the next century. Therefore, we conducted research to determine the productivity and water use of wheat under conditions as representative as possible of future fields. Using unique free-air CO2 enrichment (FACE) apparatus, we exposed open-field plots to season-long elevated CO2 concentrations under ample (wet) and limiting (dry) water conditions. The results show that under wet conditions, there is a substantial wheat yield benefit from the elevated CO2 with a slight water savings. Further, yield benefit was larger under dry conditions, which should help compensate for adverse climatic changes that may accompany the increase in atmospheric CO2. This work should help future growers develop optimum management strategies and, of course, should ultimately benefit all future food consumers.

Technical Abstract: A free-air CO2 enrichment (FACE) experiment was conducted at Maricopa, Arizona, on wheat from December 1992 through May 1993. The FACE apparatus maintained the CO2 concentration, [CO2], at 550 micro mol/mol across four replicate 25-m-dia. circular plots under natural conditions in an open field. Four matching Control plots at ambient [CO2] (about 370 micro mol/mol) were also installed in the field. In addition to the two levels of [CO2], there were ample (Wet) and limiting (Dry) levels of water supplied through a subsurface drip irrigation system. Daily latent heat flux, i.e. evapotranspiration, ET, was about 8% lower in the FACE-Wet plots, as determined from energy balance measurements. Net canopy photosynthesis was stimulated by an average 19 and 44% in the Wet and Dry plots, respectively, by elevated [CO2]. No significant acclimation or down regulation was observed. There was little above- ground growth response to elevated [CO2] early in the season when temperatures were cool. Then, as temperatures warmed into spring, the FACE plants grew about 20% more than the Control plants. Root biomass accumulation was also stimulated about 20%. The FACE plants averaged 0.6C warmer than the Controls in the well-watered plots. In May the FACE plants matured and senesced about a week earlier than the controls in the Wet plots. Because of the acceleration of sensescence, there was a shortening of the duration of grain filling, and consequently, there was a narrowing of the final biomass and yield differences. The 20% mid- season growth advantage of FACE shrunk to about an 8% yield advantage in the Wet plots, while the yield differences between FACE and Control remained at about 20% in the Dry plots.