Interactive effects of elevated CO 2 and O 3 on rice and flacca tomato

Abstract

Atmospheric concentrations of both carbon dioxide (CO 2) and ozone (O 3) are increasing, with potentially dramatic effects on plants. This study was conducted to determine interactive effects of CO 2 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 CO 2 (≈ 400 or 700 μl 1 −1 CO 2) and/or ambient or elevated O 3 (peak/valley pattern of exposure with cumulative totals of ≈ 1 or 44 μl 1 −1 h). Elevated CO 2 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 CO 2 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 CO 2 had no significant effect on the tendency for O 3-induced biomass reductions of flacca tomato. For flacca, elevated CO 2 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 0.11, respectively. This study was preliminary, as the environmental conditions in these experiments may have altered O 3 and CO 2 responses of the plants. However, these results provided additional evidence that elevated CO 2 inhibits adverse effects of O 3 on plants, and that the interactive response may be mediated by stomata.