The Loss of Structural Integrity in Damaged Spruce Needles from Locations Exposed to Air Pollution I. Mesophyll and Central Cylinder

In connection with the new type of forest damage, the individual disease situation of two-year-old spruce (Picea abies) needles was analyzed histopathologically in forest areas exposed to different levels of O3-, SO2- and NO3- pollution. Early damage results from losses of chlorophyll in the mesophyll cells. The bleaching is more intensive towards the apex in severely damaged needles. The cytoplasm is aggregated at the cell wall and the chloroplasts show definite structural damage as well. The mesophyll cells below the epidermis, or the cells adjacent to the vascular bundle sheath, appear to be particularly susceptible. Collapsed cells (bone cells), which increase in number with damage, can…