Growth response to salinity at high levels of carbon dioxide

Plants of the C₃ species Phaseolus vulgaris and Xanthium strumarium and of the C₄ salt-sensitive Zea mays and the C₄ halophyte Atriplex halimus were grown with and without NaCl salt-stress at normal (∼340 μl I^-1) and at high (∼2500 μl I^-1) ambient CO₂. In all four species growth (dry weight increment) was enhanced by CO₂ supplementation. The relative response was greater in the salinized than in the control plants. Plant tops responded more to CO, than the roots. CO₂ supplementation appears to increase plant tolerance of low levels of salinity.