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
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
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.