Fig. 1
From: Macro- and microscopic leaf injury triggered by ozone stress in beech foliage (Fagus sylvatica L.)
Cumulated phytotoxic ozone dose (POD1, Grünhage et al. 2012) for beech leaf area during the growing seasons of 2002, 2003 and 2006 (May–September) in the top canopy layer of ambient and twice ambient O3 treatment by a free-air fumigation experiment in Kranzberg Forest, Germany. Arrow heads indicate foliage harvest dates with emphasis on (i) visible O3 symptoms 2002 and 2003, (ii) histochemical analyses of visible symptoms 2003 and (iii) analyses of structural and ultrastructural cell injury 2006