Mechanisms underlying the amelioration of O<inf>3</inf>-induced damage by elevated atmospheric concentrations of CO<inf>2</inf>
- Publication Type:
- Journal Article
- Journal of Experimental Botany, 2004, 55 (397), pp. 771 - 781
- Issue Date:
There is growing evidence that rising atmospheric CO2concentrations will reduce or prevent reductions in the growth and productivity of C3crops attributable to ozone (O3) pollution. In this study, the role of pollutant exclusion in mediating this response was investigated through growth chamber-based investigations on leaves 4 and 7 of spring wheat (Triticum aestivum cv. Hanno). In the core experiments, plants were raised at two atmospheric CO2concentrations (ambient [350 μl l-1] or elevated CO2[700 μl l-1] under two O3regimes (charcoal/Purafil®-filtered air [<5 nl l-1O3] or ozone-enriched air [75 nl l-17 h d-1]). A subsequent experiment used an additional O3treatment where the goal was to achieve equivalent daily O3uptake over the life-span of leaves 4 and 7 under ambient and CO2-enriched conditions, through daily adjustment of exposures based on measured shifts in stomatal conductance. Plant growth and net CO2assimilation were stimulated by CO2-enrichment and reduced by exposure to O3. However, the impacts of O3decreased with plant age (i.e. leaf 7 was more resistant to O3injury than leaf 4); a finding consistent with ontogenic shifts in the tolerance of plant tissue and/or acclimation to O3-induced oxidative stress. In the combined treatment, elevated CO2protected against the adverse effects of O3and reduced cumulative O3uptake (calculated from measurements of stomatal conductance) by c. 10% and 35% over the life-span of leaves 4 and 7, respectively. Analysis of the relationship between O3uptake and the decline in the maximum in vivo rate of Rubisco carboxylation (Vcmax) revealed the protection afforded by CO2-enrichment to be due, to a large extent, to the exclusion of the pollutant from the leaf interior (as a consequence of the decline in stomatal conductance triggered by CO2-enrichment), but there was evidence (especially from flux-response relationships constructed for leaf 4) that CO2-enrichment resulted in additional effects that alleviated the impacts of ozone-induced oxidative stress on photosynthesis.
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