The interactive effects of elevated CO₂ and O₃ concentration on photosynthesis in spring wheat

This study investigated the interacting effects of carbon dioxide and ozone on photosynthetic physiology in the flag leaves of spring wheat (Triticum aestivum L. cv. Wembley), at three stages of development. Plants were exposed throughout their development to reciprocal combinations of two carbon dioxide and two ozone treatments: [CO₂] at 350 or 700 μmol mol^-1, [O₃] at < 5 or 60 nmol mol^-1. Gas exchange analysis, coupled spectrophotometric assay for RuBisCO activity, and SDS-PAGE, were used to examine the relative importance of pollutant effects on i) stomatal conductance, ii) quantum yield, and iii) RuBisCO activity, activation, and concentration. Independently, both elevated [CO₂] and elevated [O₃] caused a loss of RuBisCO protein and V_cmax. In combination, elevated [CO₂] partially protected against the deleterious effects of ozone. It did this partly by reducing stomatal conductance, and thereby reducing the effective ozone dose. Elevated [O₃] caused stomatal closure largely via its effect on photoassimilation.