Effects of wind and abrasion on cuticular integrity in Fagus sylvatica L. and consequences for transfer of pollutants through leaf surfaces

Abstract

The transfer of pollutants from the atmosphere to the internal tissues of a leaf may involve several routes and physical processes. Wind and abrasive damage, which are components of weathering, cause changes in leaf surface characteristics and cuticular integrity which influence gaseous diffusion and the uptake of solutes. Wind-induced components of weathering of individual leaves of Fagus sylvatica were simulated by the use of a miniature wind tunnel and surface abrasion. The consequence of exposure to wind was widespread disruption of trichomes, and evidence of smoothing of cuticular wax was obtained using low-temperature scanning electron microscopy (SEM). An abrasive treatment also damaged trichomes, created cuticular lesion visible by SEM and significantly increased total surface conductance, to water vapour, on both adaxial (astomatous) and abaxial (stomatous) surfaces. The structural integrity of the cuticle and the spatial distribution of cuticular lesions was investigated by using ruthenium red as a convenient dye tracer. Leaves were found to be most susceptible to abrasive damage on their abaxial surfaces, where the spatial distribution of lesions was significantly clustered. The occurrence of these lesions may be related to a natural structural and conductive heterogeneity across the leaf surface. Sites most vulnerable to damage were trichomes and protruding veins. Exposure of F. sylvatica leaves to natural weathering processes in an exposed upland site increased uptake of ( 35S) sulphate from droplets placed on the adaxial cuticle by 30-fold on average compared with leaves grown in a sheltered location at the same altitude. The spatial heterogeneity of sulphate uptake measured at discrete points over a single leaf was also greater in leaves from the exposed site. Consequently, weathering may increase the heterogeneity of gas exchange and the uptake of solutes, by increasing leakiness at localised sites across the leaf surface.