Photosynthetic response to growth temperature and CO₂ enrichment in two species of C₄ grasses

Plants of Echinochloa crus-galli from Québec, North Carolina, and Mississippi and of Eleusine indica from Mississippi were grown under three thermoperiods (28:22, 24:18, 21:15 °C) and two atmospheric CO 2 concentrations (350 and 675 μL ∙ L −1 ). CO 2 enrichment induced an increase in net photosynthesis and in dark respiration for all populations. Neither conductance, transpiration, nor the transpiration/photosynthesis ratio were affected by CO 2 enrichment. Plants showed higher photosynthetic and dark respiration rates when grown in warm regimes. Stomatal conductance did not vary with growth temperature. Cool-adapted plants from Québec maintained the overall highest net photosynthesis and respiration. Plants originating from warm areas had a weaker acclimation potential to low temperature than those from cool environments.