Differential response of cultivated and weedy (red) rice to recent and projected increases in atmospheric carbon dioxide

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 mu mol 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 mu mol mol(-1). By 55 DAS, significant CO2 by type (RRvs. 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 mu mol 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.