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WEED MANAGEMENT

Differential Response of Cultivated and Weedy (Red) Rice to Recent and Projected Increases in Atmospheric Carbon Dioxide

^a USDA-ARS, Crop Systems and Global Change Lab., Beltsville, MD 20705
^b USDA-ARS, Dale Bumpers National Rice Res. Cent., Stuttgart, AR

^* Corresponding author (l.ziska{at}ars.usda.gov).

To determine whether recent or projected increases in atmospheric [CO₂] favor cultivated rice or its weedy relative, red rice, we examined the initial growth and vegetative characteristics of these two groups using six weedy red rice (RR) biotypes and six cultivated rice (CR) varieties at CO₂ concentrations that corresponded to the 1940s, current levels, and that projected for the middle of this century (300, 400, and 500 µmol mol^–1, respectively). Increasing [CO₂] resulted in significant increases in initial leaf area and root weight for the RR, as early as 27 d after sowing (DAS) at 500 µmol mol^–1. By 55 DAS, significant CO₂ by type (RR vs. CR) interactions were observed with RR demonstrating a 55 and 62% increase in plant biomass and leaf area, respectively, relative to the CR at 500 µmol mol^–1 [CO₂]. Overall, these results indicate a greater physiological plasticity and genetic diversity among RR relative to CR that may impact weed/crop competition as atmospheric CO₂ increases. However, this greater variation may also provide a unique genetic resource that could be incorporated into CR varieties to increase their adaptability to rising atmospheric CO₂.

Abbreviations: DAS, d after sowing • PAR, photosynthetically active radiation • RR, weedy red rice biotypes • CR, cultivated rice varieties

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Received for publication October 1, 2007.