Abstract
Plants of Echinochloa crus-galli from Québec and Mississippi were grown under two thermoperiods (28 degrees C/22 degrees C, 21 degrees C/15 degrees C) and two atmospheric CO(2) concentrations (350 and 675 microliters per liter) to examine possible differential responses of northern and southern populations of this C(4) grass species. Translocation was monitored using radioactive tracing with short-lived (11)C. CO(2) enrichment induced a decrease in the size of the export pool in plants of both populations. Other parameters did not strongly respond to elevated CO(2). Low temperature reduced translocation drastically for plants from Mississippi in normal CO(2) concentration, but this reduction was ameliorated at high CO(2). Overall, plants from Québec had a higher (11)C activity in leaf phloem and a higher percentage of (11)C exported, whereas these northern plants had lower turnover time and smaller pool size than plants from the southern population.