Does elevated CO2 ameliorate the impact of O-3 on chlorophyll content and photosynthesis in potato (Solanum tuberosum)?

This study examined the impact of season-long exposure to elevated carbon d ioxide (CO2) and ozone (O-3), individually and in combination, on leaf chlo rophyll content and gas exchange characteristics in potato (Solanum tuberos um L. cv. Bintje), Plants grown in open-top chambers were exposed to three CO, (ambient, 550 and 680 mu mol mol(-1)) and two O-3 treatments (ambient a nd elevated; 25 and 65 nmol mol(-1), 8 h day(-1) means, respectively) betwe en crop emergence and maturity; plants were also grown in unchambered field plots. Non-destructive measurements of chlorophyll content and visible fol iar injury were made for all treatments at 2-week intervals between 43 and 95 days after emergence, Gas exchange measurements were made for all except the intermediate 550 mu mol mol(-1) CO2 treatment. Season-long exposure to elevated O-3 under ambient CO2 reduced chlorophyll content and induced ext ensive visible foliar damage, but had little effect on net assimilation rat e or stomatal conductance. Elevated CO2 had no significant effect on chloro phyll content, but greatly reduced the damaging impact of O-3 on chlorophyl l content and visible foliar damage. Light-saturated assimilation rates for leaves grown under elevated CO2 were consistently lower when measured unde r either elevated or ambient CO2 than in equivalent leaves grown under ambi ent CO2. Analysis of CO2 response curves revealed that CO2-saturated assimi lation rate, maximum rates of carboxylation and electron transport and resp iration decreased with time. CO2-saturated assimilation rate was reduced by elevated O-3 during the early stages of the season, while respiration was significantly greater under elevated CO2 as the crop approached maturity. T he physiological origins of these responses and their implications for the performance of potato in a changing climate are discussed.