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The role of ozone flux and antioxidants in the suppression of ozone injury by elevated CO₂ in soybean

Booker, Fitzgerald L., Fiscus, Edwin L.
Journal of experimental botany 2005 v.56 no.418 pp. 2139-2151
Glycine max, soybeans, field crops, antioxidants, ozone, carbon dioxide, plant damage, phytotoxicity, photosynthesis, plant growth, crop yield, superoxide dismutase, glutathione reductase (NADPH), peroxidase, enzyme activity, glutathione, ascorbic acid
The projected rise in atmospheric CO₂ concentration is expected to increase growth and yield of many agricultural crops. The magnitude of this stimulus will partly depend on interactions with other components of the atmosphere such as tropospheric O₃. Elevated CO₂ concentrations often lessen the deleterious effects of O₃, but the mechanisms responsible for this response have received little direct examination. Previous studies have indicated that protection against O₃ injury by elevated CO₂ can be attributed to reduced O₃ uptake, while other studies suggest that CO₂ effects on anti-oxidant metabolism might also be involved. The aim of this experiment was to test further the roles of O₃ flux and antioxidant metabolism in the suppression of O₃ injury by elevated CO₂. In a two-year experiment, soybean [Glycine max (L.) Merr.] was exposed from emergence to maturity to charcoal-filtered air or charcoal-filtered air plus a range of O₃ concentrations in combination with ambient or approximately twice-ambient CO₂ concentrations in open-top field chambers. Experimental manipulation of O₃ concentrations and estimates of plant O₃ uptake indicated that equivalent O₃ fluxes that suppressed net photosynthesis, growth, and yield at ambient concentrations of CO₂ were generally much less detrimental to plants treated concurrently with elevated CO₂. These responses appeared unrelated to treatment effects on superoxide dismutase, glutathione reductase, and peroxidase activities and glutathione concentration. Total ascorbic acid concentration increased by 28-72% in lower canopy leaves in response to elevated CO₂ and O₃ but not in upper canopy leaves. Increasing concentrations of atmospheric CO₂ will likely ameliorate O₃ damage to many crops due to reduced O₃ uptake, increased carbon assimilation, and possibly as yet undetermined additional factors. The results of this study further suggest that elevated CO₂ may increase the threshold O₃ flux for biomass and yield loss in soybean.