Vegetative growth of soybean as affected by elevated carbon dioxide and ozone Original Research Article

The effects of elevated carbon dioxide (CO2) and ozone (03) on soybean (Glycine max (L.) Merr. cv. Centennial) growth and biomass partitioning were evaluated under greenhouse conditions. Soybeans were exposed to CO2 concentrations at 350 (ambient), 450, 550, and 650 μl liter1 (ppm) for 24 h day−1 for 5 weeks. Ozone treatments of 0 and 120 nl liter−1 (ppb) for 6 h day−1 for 5 days week−1 for 5 weeks were added in combination with the CO2 treatments. Plant dry weight and biomass partitioning were assessed each week. Dry weight of leaf, stem, and root, as well as the total plant dry weight increased with exposure to increasing levels of CO2. Dry weight of leaf, root and total plant were suppressed significantly by the 03 treatment. Stem dry weight was not affected by O3. Suppression of root dry weight due to 03 at each weekly harvest was significantly dependent on the CO2 concentration. Root growth was enhanced by CO2 at 650 μl liter−1 compared with ambient CO2 (350 μl liter−1) at 5 weeks of age. At ambient CO2 in the presence of 03 the roots were only about 63% of the weight of the root grown in the absence of O3. At 550 and 650 μl liter−1 CO2 the biomass of soybean roots in the presence of 120 nl liter−1 O3 was 88•2 and 88•4% of the control, respectively. Thus, CO2 limited the amount of root growth suppression caused by 03. The partitioning of leaf, stem, and root dry weight in relation to total plant dry weight remained relatively constant across each CO2 concentration. Thus, CO2 did not affect biomass partitioning among leaves, stems and roots of soybean.