Elevated Carbon Dioxide and Ozone Effects on Peanut: I. Gas‐Exchange, Biomass, and Leaf Chemistry

The effects of elevated CO 2 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 CO 2 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 CO 2 (about 375 μmol mol −1 ) and CO 2 enrichment of approximately 173 and 355 μmol mol −1 in combination with charcoal‐filtered air (22 nmol O 3 mol −1 ), nonfiltered air (46 nmol O 3 mol −1 ), and nonfiltered air plus O 3 (75 nmol O 3 mol −1 ). Twice‐ambient CO 2 in charcoal‐filtered air increased A by 23% while decreasing seasonal stomatal conductance (g s ) by 42%. Harvest biomass was increased 12 to 15% by elevated CO 2 In ambient CO 2 , nonfiltered air and added O 3 lowered A by 21% and 48%, respectively, while added O 3 reduced g s by 18%. Biomass was not significantly affected by nonfiltered air, but was 40% lower in the added O 3 treatment. Elevated CO 2 generally suppressed inhibitory effects of O 3 on A and harvest biomass. Leaf starch concentration was increased by elevated CO 2 and decreased by O 3 Treatment effects on foliar N and total phenolic concentrations were minor. Increasing atmospheric CO 2 concentrations should attenuate detrimental effects of ambient O 3 and promote growth in peanut but its effectiveness declines with increasing O 3 concentrations.