The objective of this study was to determine how elevated CO2 and temperature affected early growth and competition between direct seeded rice (Oryza sativa) and a common paddy weed (Echinochloa glabrascens). By using temperature gradient chambers. Rice and E. glabrescens were grown for 5 weeks at ratios of 1:0. 3:1 and 0:1 at three temperatures (16.4℃, 19.8℃, and 22.2℃) and either in ambient (361ppm) or elevated (566ppm) CO2. For both species. elevated CO2 had no effect on mainstem leaf number while air temperature had a slight positive effect which was greater in E. glabrescens than rice. With elevated CO2 rice leaf area index and plant height increased alightly in all species combinations but no increases were observed for E. Glabuescens. For rice in all combinations. elevated CO2 tended to increase the rot and total biomass much more than any other growth parameters: the increases in root and total biomass resulting from elevated CO2 ranged from 16% to 40%. depending on air temperature. At the lowest temperature, the decrease in rice biomass in combination with E. glabrescens was significantly greater at elevated CO2 (18%) than ambient CO2 (3%). At the highest temperature, however, the decrease in rice biomass at elevated CO2 (22%) was less than that at ambient CO2 (36%). The competitive ability of rice as measured by the decrease in biomass when grown in combination with E. glabrescens depended strongly on root growth and/or allocation. These results suggest that at higher temperatures elevated CO2 could enhance the competitive ability of direct seeded rice during early growth. However, at lower temperatures. the competitive ability of E. glabrescens seems to be greater.

• Han-Yong Kim