The effects of interacting carbon dioxide and ozone on the carbon balance of aspen (Populus tremuloides Michx.) grown in an open-air carbon dioxide and ozone enrichment system

The concentrations of tropospheric ozone (O₃) and carbon dioxide (CO₂) have been increasing due to large-scale consumption of fossil fuels during the last one-and-half century. These two anthropogenic air pollutants are major contributors to global warming—the greenhouse effect. Elevated CO₂ generally stimulates plant growth, at least in the short term, whereas elevated O₃ impairs metabolism by non-specifically reacting with lipids, proteins and nucleic acids thus disrupting the functional and structural integrity of the cell. The individual effects of elevated CO ₂ and O₃ have been studied in great detail, but the interactive effect of these two gases has received attention only recently. The opposite effects of these two gases have been found to cancel each other out in some species, whereas in others the negative effects of O₃ were enhanced at the presence of elevated CO₂, i.e. the question of potential amelioration effect has not been unequivocally answered. In current work a method is proposed to evaluate the interactive effects of elevated CO ₂ and O₃. In addition, (i) the relative role of stomatal and mesophyll processes is quantified in limiting photosynthesis under elevated CO₂ and O₃ and (ii) the relationship between leaf- and plant-level carbon gain is analyzed.