Fig. 5.

Differences in ¹³C discrimination between ozone-treated and control plants, ΔΔ (90/40 day/night versus <3 nl O₃ l^–1). ‘Leaf’ and ‘Stem’ refer to leaf and stem cellulose of Betula pendula, respectively. LF and HF refer to plants grown with low and high amounts of fertilizer, respectively. Solid bars: measured ΔΔ values. Dashed bars: expected ΔΔ values. Expected ΔΔ values were estimated using a model by Farquhar et al. (1982). This model describes ¹³C discrimination associated with plant carbon uptake including CO₂ diffusion into plant leaves and assimilation by Rubisco. Numbers inside bars denote differences between measured and expected ΔΔ values. Statistically significant differences are marked by asterisks (one-tailed t-test: ∗P<0.05; ∗∗P<0.01). The difference of the Leaf/HF treatment is close to being statistically significant (P<0.08). This analysis is based on data published by Saurer et al. (1995).