THE LOSS OF STRUCTURAL INTEGRITY IN DAMAGED SPRUCE NEEDLES FROM LOCATIONS EXPOSED TO AIR-POLLUTION .2. EPIDERMIS AND STOMATA (DERMAL TISSUE)

Abstract Within the framework of appraising the new type of forest damage, the epidermis of two‐year‐old spruce (Picea abies) needles was investigated as a possible site for primary attack by air pollutants using light and scanning electron microscopy. Depending upon the extent of the macroscopically visible needle leaf disease, a degeneration process of the cuticular, stomatal and epidermal structures leading to the lethal destruction of the needle surface was observed. Stomatal and epidermal cells become increasingly deformed or collapsed showing increasing discolouration due to phenolic deposits. Additionally, the erosion of stomatal waxes is accelerated, leading initially to a temporary occlusion of the stomata, and then to a wide opening of the antechamber following a complete decomposition of the plug. Surface lesions indicating early damage to the epidermal tissue already occur on slightly yellowed needles. The barrier effect of the spruce needle epidermis on exogenous stressors could thereby already be reduced at an early stage, triggering incipient losses of structural resistance. Copyright © 1990, Wiley Blackwell. All rights reserved