Interactive Effects of O3 and CO2: Implications for Terrestrial Ecosystems

The atmosphere supplies plants with CO2 for carbon fixation, producing carbon-containing compounds for structure and function of cells; and O2 to oxidize these carbon compounds, producing cellular energy. Recently, human activities have produced increases in both CO2 and O3, a highly reactive form of O2. Ozone and CO2, generally have “detrimental” and “beneficial” effects on plants, respectively. However, the combined impacts of both gases on vegetation are uncertain despite their co-occurrence. To date, effects of O3 and CO. usually have been defined narrowly in terms of plant shoot responses (leaf biochemistry, physiology, crop yield or tree biomass). However, plants do not exist in a vacuum, but as part of an ecosystem whose condition can be defined by studying basic processes. Thus, the objectives of this review are: (1) to review the literature concerning interactive effects of O3 and CO2 on vegetation; and, (2) to carry out this evaluation in the context of terrestrial ecosystem processes, i.e., carbon and nitrogen cycling.