Mechanisms underlying the amelioration of O3-induced damage by elevated atmospheric concentrations of CO2

Abstract

There is growing evidence that rising atmospheric CO2 concentrations will reduce or prevent reductions in the growth and productivity of C3 crops 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 CO2 concentrations (ambient [350 micro l l(-1)] or elevated CO2 [700 micro l l(-1)] under two O3 regimes (charcoal/Purafil-filtered air [<5 nl l(-1) O3] or ozone-enriched air [75 nl l(-1) 7 h d(-1)]). A subsequent experiment used an additional O3 treatment where the goal was to achieve equivalent daily O3 uptake 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 CO2 assimilation were stimulated by CO2-enrichment and reduced by exposure to O3. However, the impacts of O3 decreased with plant age (i.e. leaf 7 was more resistant to O3 injury 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 CO2 protected against the adverse effects of O3 and reduced cumulative O3 uptake (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 O3 uptake 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.

Differential drought-induced modulation of ozone tolerance in winter wheat species

“…The winter wheat species examined displayed significant reductions in A sat , g s , V cmax , J max , R, and CE in response to O 3 , in general agreement with reports for spring wheat (Farage and Long, 1999; Cardoso-Vilhena et al , 2004). However, the results indicate that the O 3 -induced decrease in A sat might be due to both enzymatic and stomatal limitation as evidenced by the O 3 -induced reduction in g s and increase in C i accompanied by decreases in V cmax , CE, and R. The observed reduction in A sat and considerable decline in V cmax indicated that these effects might be attributable to a decrease in the quantity of active Rubisco (Farage and Long, 1999; Cardoso-Vilhena et al , 2004).…”

“…However, the results indicate that the O 3 -induced decrease in A sat might be due to both enzymatic and stomatal limitation as evidenced by the O 3 -induced reduction in g s and increase in C i accompanied by decreases in V cmax , CE, and R. The observed reduction in A sat and considerable decline in V cmax indicated that these effects might be attributable to a decrease in the quantity of active Rubisco (Farage and Long, 1999; Cardoso-Vilhena et al , 2004). The photosynthetic rate under light- and CO 2 -saturating conditions may be significantly reduced by elevated O 3 , as indicated by the reduction in J max .…”

Spectral reflectance from a soybean canopy exposed to elevated CO2 and O3

“…Averaged across the 2003–2004 growing seasons at SoyFACE, elevated CO 2 alone increased photosynthesis by 27% while elevated CO 2 in combination with elevated O 3 increased photosynthesis by 19% (Bernacchi et al , 2006). Elevated CO 2 often compensates for the negative effects of elevated O 3 on productivity by decreasing stomatal conductance and reducing O 3 diffusion into the leaf (Fiscus et al , 1997; Reid and Fiscus, 1998; Cardoso-Vilhena et al , 2004; Booker and Fiscus, 2005). …”

“…While elevated atmospheric CO 2 may increase leaf-level photosynthesis, leaf area index (leaf area per unit ground area, LAI) and overall productivity of soybean (Ainsworth et al , 2002; Long et al , 2004; Dermody et al , 2006), growth in elevated O 3 generally has the opposite effects (Morgan et al , 2003; Long et al , 2005; Dermody et al , 2006), and elevated CO 2 may partially mitigate the negative effects of elevated O 3 when plants are exposed to elevated CO 2 and elevated O 3 simultaneously (Cardoso-Vilhena et al , 2004; Booker and Fiscus, 2005; Dermody et al , 2008). As global concentrations of CO 2 and O 3 continue to increase, it will be necessary to understand their effects on the structure and physiological properties of plant canopies.…”

Effects of the interaction between ozone and carbon dioxide on gas exchange, ascorbic acid content, and visible leaf symptoms in rice leaves

“…However, the underlying mechanisms of the interaction between O 3 and CO 2 still remain uncertain (Unthworth and Hogsett 1996, Lee 2000, Morita and Tanaka 2002, Vandermeiren et al 2002, Cardoso-Vilhena et al 2004, Weigel 2004. Therefore, we wanted to know how detrimental O 3 and promotive CO 2 interact and thereby affect the photosynthesis and production processes of rice, because observations of the combined effect of O 3 and elevated CO 2 on this Asian staple food crop are few and limited only to its growth response (Olszyk andWise 1997, Ookoshi andImai 1998).…”