Effects of CO2 enrichment and temperature on growth in two C4 weeds, Echinochloa crus-galli and Eleusine indica

Mathematical growth analyses were carried out on two C4 grasses, Echinochloa crus-galli and Eleusine indica, to test the influence of CO2 enrichment and temperature on growth. Echinochloa populations from Québec, North Carolina, and Mississippi and a single population of Eleusine from Mississippi were grown for 48 days at two CO2 concentrations (350 and 675 μL∙L−1) and three temperature regimes (28:22, 24:18, and 21:15 °C). CO2 enrichment generated an increased root dry weight and induced an earlier development of inflorescences. Net assimilation rate, the only other parameter to respond to CO2 enrichment, was higher for plants grown at high CO2 concentrations during the first harvest interval. Biomass partitioning was affected by temperature. Root dry weight was greater in plants grown at 21:15 °C while more leaf area was produced in warmer temperature regimes. Only plants from Québec maintained normal growth rates under the 21:15 °C regime, suggesting that northern C4 plants are better suited for growth at low temperatures than southern ones.