Interactive effects of elevated CO2 and O-3 on rice and flacca tomato

Atmospheric concentrations of both carbon dioxide (CO2) and ozone (O-3) are increasing, with potentially dramatic effects on plants. This study was conducted to determine interactive effects of CO2 and O-3 on rice (Oryza sativa L. cv. IR 74) and a 'wilty' mutant of tomato (Lycopersicon esculentum Mill. flacca). Plants were grown from seed in a glasshouse and exposed for 28 days to ambient or elevated CO2 (approximate to 400 or 700 mu l l(-1) CO2) and/or ambient or elevated O-3 (peak/valley pattern of exposure with cumulative totals of approximate to 1 or 44 mu l l(-1) h). Elevated CO2 alleviated O-3-associated decreases in allocation of biomass to roots, as indicated by a decreased root:shoot ratio (p < 0.05), and also reduced injury from O-3 as indicated by leaf greenness readings for one experiment(p < 0.05). By itself, elevated CO2 resulted in increases in total plant and individual organ(root, leaf, stem) dry weights and root:shoot ratio and elevated O-3 resulted in increases in main culm leaf number and a decrease in stem dry weight (p < 0.05). Elevated CO2 had no significant effect on the tendency for O-3-induced biomass reductions of flacca tomato. For flacca, elevated CO2 alone increased shoot and root biomass (p < 0.05), and elevated O-3 alone tended to decrease biomass for both parameters, but only at p = 0.09 and O.11, respectively. This study was preliminary, as the environmental conditions in these experiments may have altered O-3 and CO2 responses of the plants. However, these results provided additional evidence that elevated CO2 inhibits adverse effects of O-3 on plants, and that the interactive response may be mediated by stomata. (C) 1997 Elsevier Science B.V.