Brassica rapa L. (rapid-cycling Brassica), was grown in environmentally controlled chambers to determine the interactive effects of ozone (O3) and increased root temperature (RT) on biomass, reproductive output, and photosynthesis. Plants were grown with or without an average treatment of 63 ppb O3. RT treatments were 13°C (LRT) and 18°C (HRT). Air temperatures were 25°C/15°C day/night for all RT treatments.

Ozone affected plant biomass more than did root temperature. Plants in O3 had significantly smaller total plant d. wt, shoot weight, leaf weight, leaf area and leaf number than plants grown without O3. LRT plants tended to have slightly smaller total plant d. wt, shoot weight, root weight, leaf weight, leaf area, and leaf number than HRT plants. For all variables, LRT plants grown in O3 had the smallest biomass, and plants grown in HRT without O3 had the largest biomass.

Ozone reduced both fruit weight and fruit number; LRT also reduced fruit weight but had no effect on fruit number. Ozone reduced photosynthesis but RT had no effect. Conductance and internal CO2 were unaffected by O3 or RT.

These studies indicate that plant growth with LRT might be more reduced in the presence of O3 than growth in plants with HRT, which might be able to compensate for O3-caused reductions in photosynthesis to avoid decreased biomass and reproductive output.