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Keywords:

  • cumulative O3 uptake;
  • Fagus sylvatica (European beech);
  • multivariate analysis;
  • ozone (O3);
  • principal component analysis (PCA)

Summary

  • Increasing atmospheric concentrations of phytotoxic ozone (O3) can constrain growth and carbon sink strength of forest trees, potentially exacerbating global radiative forcing. Despite progress in the conceptual understanding of the impact of O3 on plants, it is still difficult to detect response patterns at the leaf level.
  • Here, we employed principal component analysis (PCA) to analyse a database containing physiological leaf-level parameters of 60-yr-old Fagus sylvatica (European beech) trees. Data were collected over two climatically contrasting years under ambient and twice-ambient O3 regimes in a free-air forest environment.
  • The first principal component (PC1) of the PCA was consistently responsive to O3 and crown position within the trees over both years. Only a few of the original parameters showed an O3 effect. PC1 was related to parameters indicative of oxidative stress signalling and changes in carbohydrate metabolism. PC1 correlated with cumulative O3 uptake over preceding days.
  • PC1 represents an O3-responsive multivariate pattern detectable in the absence of consistently measurable O3 effects on individual leaf-level parameters. An underlying effect of O3 on physiological processes is indicated, providing experimental confirmation of theoretical O3 response patterns suggested previously.