Effects of Elevated CO2 and Temperature on Competition between Rice and Echinochloa glabrescens Seedlings

The objective of this study was to determine how elevated CO. and temperature affected early growth and competition between direct seeded rice (Orsa sativa) and a common paddy weed (Echinochlou glabrescens). 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 ( 16.7° C. 19.8°C, and 22.2° C) and either in ambient (361 ppm) or elevated (566ppm) CO.. For both species, elevated CO: 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 CO., rice leaf area index and plant height increased slightly in all species combinations but no increases were observed for E. glabrescens. For rice in all combinations, elevated CO: tended to increase the root and total biomass much more than any other growth parameters: the increases in root and total biomass resulting from elevated CO: ranged from 16% to 10%, depending on air temperature. At the lowest temperature, the decrease in rice biomass in combination with E. glabrescens was significantly greater at elevated CO: (18%) than ambient CO: (3%). Al the highest temperature, however, the decrease in rice biomass at elevated CO: (22%) was less than that at ambient CO: (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 CO: 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.