PHYSICAL INJURY, RE-CRYSTALLIZATION OF WAX TUBES AND ARTIFACTS - IDENTIFYING SOME CAUSES OF STRUCTURAL ALTERATION TO SPRUCE NEEDLE WAX

The study presents investigations of epicuticular wax morphology on sp ruce needles (Picea abies (L.) Karst.) performed by ambient temperatur e scanning electron microscopy. To use alterations to epicuticular wax morphology as a successful tool in forest damage research, it is nece ssary to distinguish environmental influences and artefacts from commo n pollution effects. The present paper summarizes observations of alte rations to epicuticular waxes independent of pollution effects, record ed in various field studies. These observations are supplemented by co ntrolled experiments to investigate wax alterations owing to solvents and mechanical injury. Fissures in the antechamber wax were the result of needle shrinkage during drying. Wax alterations, where only the an techamber wax was affected by a continuous loss of the structural inte grity of wax tubes, were classified as storage artefacts since they oc curred exclusively on needles stored in air-tight glass vials and were unrelated to needle age, sampling site or pollution influence. Such w ax alterations were never observed in needles stored in air-permeable paper bags. Mechanical injury also resulted in severe morphological al terations to epicuticular wax structures. The wax tubes on the surface as well as in the antechamber were squashed and flattened. On smoothe d and squashed wax layers a significant regrowth of wax tubes was occa sionally observed, unrelated to needle age. Though the tubular form of the re-crystallized waxes was similar to those originally present on the surface, the tube diameters were much wider. Since redeveloped wax tubes also occurred on dead needles which had been artificially injur ed, this process could be classified as re-crystallization analogous t o wax re-crystallization out of solvent extracts. The re-crystallizati on took place within 48 h after the mechanical injury occurred. The im plications of the reported wax alterations for a successful use of epi cuticular wax morphology as a bioindicator are discussed.