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

The effects of elevated C[O.sub.2] and ozone ([O.sub.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 C[O.sub.2] and [O.sub.3] mixtures on leaf gas-exchange, harvest biomass, and leaf chemistry in peanut (Arachis hypogaea L.), an [O.sub.3]-sensitive species, using open-top field chambers. Treatments included ambient C[O.sub.2] (about 375 [micro]mol [mol.sup.-1]) and C[O.sub.2] enrichment of approximately 173 and 355 [micro]mol [mol.sup.-1] in combination with charcoal-filtered air (22 nmol [O.sub.3] [mol.sup.-1]), nonfiltered air (46 nmol [O.sub.3] [mol.sup.-1]), and nonfiltered air plus [O.sub.3] (75 nmol [O.sub.3] [mol.sup.-1]). Twice-ambient C[O.sub.2] in charcoal-filtered air increased A by 23% while decreasing seasonal stomatal conductance ([g.sub.s]) by 42%. Harvest biomass was increased 12 to 15% by elevated C[O.sub.2]. In ambient C[O.sub.2], nonfiltered air and added [O.sub.3] lowered A by 21% and 48%, respectively, while added [O.sub.3] reduced [g.sub.s] by 18%. Biomass was not significantly affected by nonfiltered air, but was 40% lower in the added [O.sub.3] treatment. Elevated C[O.sub.2] generally suppressed inhibitory effects of [O.sub.3] on A and harvest biomass. Leaf starch concentration was increased by elevated C[O.sub.2] and decreased by [O.sub.3]. Treatment effects on foliar N and total phenolic concentrations were minor. Increasing atmospheric C[O.sub.2] concentrations should attenuate detrimental effects of ambient [O.sub.3] and promote growth in peanut but its effectiveness declines with increasing [O.sub.3] concentrations.