• air pollution;
  • climate change;
  • N allocation;
  • primary metabolism;
  • senescence


Both elevated ozone (O3) and limiting soil nitrogen (N) availability negatively affect crop performance. However, less is known about how the combination of elevated O3 and limiting N affect crop growth and metabolism. In this study, we grew tobacco (Nicotiana sylvestris) in ambient and elevated O3 at two N levels (limiting and sufficient). Results at the whole plant, leaf, and cellular level showed that primary metabolism was reduced by growth in limiting N, and that reduction was exacerbated by exposure to elevated O3. Limiting N reduced the rates of photosynthetic CO2 uptake by 40.8% in ambient O3-exposed plants, and by 58.6% in elevated O3-exposed plants, compared with plants grown with sufficient N. Reductions in photosynthesis compounded to cause large differences in leaf and whole plant parameters including leaf number, leaf area, and leaf and root biomass. These results were consistent with our meta-analysis of all published studies of plant responses to elevated O3 and N availability. In tobacco, N uptake and allocation was also affected by growth in limiting N and elevated O3, and there was an O3-induced compensatory response that resulted in increased N recycling from senescing leaves. In addition, transcript-based markers were used to track the progress through senescence, and indicated that limiting N and elevated O3, separately and in combination, caused an acceleration of senescence. These results suggest that reductions in crop productivity in growing regions with poor soil fertility will be exacerbated by rising background O3.