The impact of ozone on juvenile maize (Zea mays L.) plant photosynthesis: Effects on vegetative biomass, pigmentation, and carboxylases (PEPc and Rubisco)

The impact of ozone on crops was more studied in C3 than in C4 species. In C3 plants, ozone is known to induce a photosynthesis impairment that can result in significant depressions in biomass and crop yields. To investigate the impact of O3 on C4 plant species, maize seedlings (Zea mays L. cv. Chambord) were exposed to 5 atmospheres in open-top chambers: non-filtered air (NF, 48 nL L-1 O3) and NF supplied with 20 (+ 20), 40 (+ 40), 60 (+ 60), and 80 (+ 80) nL L-1 ozone. An unchambered plot was also available. Leaf area, vegetative biomass, and leaf dry mass per unit leaf area (LMA) were evaluated 33 days after seedling emergence in OTCs. At the same time, photosynthetic pigments as well as carboxylase (PEPc and Rubisco) activities and amounts were also examined in the 5th leaf. Ozone enhanced visible symptoms characterizing foliar senescence. Across NF, + 20, + 40, and + 60 atmospheres, both chlorophylls and carotenoids were found to be linearly decreased against increasing AOT40 (ca. - 50 % in + 60). No supplementary decrease was observed between + 60 and + 80. Total above-ground biomass was reduced by 26 % in + 80 atmosphere; leaf dry matter being more depressed by ozone than leaf area. In some cases, LMA index was consistent to reflect low negative effects caused by a moderate increase in ozone concentration. PEPc and Rubisco were less sensitive to ozone than pigments: only the two highest external ozone doses reduced their activities by about 20 - 30 %. These changes might be connected to losses in PEPc and Rubisco proteins that were decreased by about one-third. The underlying mechanisms for these results were discussed with special reference to C3 species. To conclude, we showed that both light and dark reactions of C4 photosynthesis can be impaired by realistic ozone doses.