Elevated carbon dioxide and ozone effects on peanut: I. Gas-exchange, biomass, and leaf chemistry

The effects of elevated CO2 and ozone (O-3) on net photosynthetic rate (A) and growth are generally antagonistic although plant responses are highly dependent on crop sensitivity to the individual gases and their concentrations. In this experiment, we evaluated the effects of various CO2 and O-3 mixtures on leaf gas-exchange, harvest biomass, and leaf chemistry in peanut (Arachis hypogaea L.), an O-3-sensitive species, using open-top field chambers. Treatments included ambient CO2 (about 375 mu mol mol(-1)) and CO2 enrichment of approximately 173 and 355 mu mol mol-1 in combination with charcoal-filtered air (22 nmol O-3. mol(-1)), nonfiltered air (46 nmol 03 mol-1), and nonfiltered air plus O-3 (75 nmol O-3 mol(-1)). Twice-ambient CO in charcoal-filtered air increased A by 23% 2 while decreasing seasonal stomatal conductance (g) by 42%. Harvest biomass was increased 12 to 15% by elevated CO2. In ambient CO2, nonfiltered air and added O-3 lowered A by 21% and 3 48%, respectively, while added,O-3, reduced g, by 18%. Biomass was not significantly affected by nonfiltered air, but was 40% lower in the added O-3 treatment. Elevated CO2 generally suppressed i inhibitory effects of O-3. on A and harvest biomass. Leaf starch concentration was increased i by elevated CO, and decreased by O-3. Treatment effects on foliar N and total phenolic coni centrations were minor. Increasing atmospheric CO2 concentrations should attenuate detrimental effects of ambient O-3 and promote growth in peanut but its effectiveness declines with increasing O-3 concentrations.