Effects of wind and simulated acid mist on leaf cuticles

The combined effect of wind and simulated acid mist on leaf cuticles was investigated in beech (Fagus sylvatica L.) and birch (Betula pubescens Ehr.). Macroscopic and microscopic features of wind damage are described. Visibly damaged leaf area and the numbers of microscopic cuticular lesions were measured. The cuticular conductance to water vapour (gc) of the astomatous adaxial surfaces of the leaves was measured by a gravimetric method.

Field experimental sites were selected to provide either: 1] Direct wind action on widely-spaced plants caused by high wind speed and impaction of wind-blown particles, but with minimal mutual leaf abrasion 2] Indirect wind action via a high degree of mutual abrasion between closely-spaced plants. Direct wind action increased water loss via the leaf adaxial cuticle twoto three-fold in each species, by increasing the numbers of microscopic cuticular lesions. Indirect wind action caused more visible damage to leaves than Indirect wind action, increased gc by about threefold compared with complete shelter, and induced the most cuticular lesions.

Acid mists at pH 3 or pH 5 were applied to the plants in situ at weekly intervals over a 100-day period. In sheltered plants, no effect of acid mist was detected on visibly damaged leaf area, the numbers of microscopic cuticular lesions, or on gc. However, acid mists in combination with wind exposure caused significant effects on cuticular integrity that were dependent on the type of wind action. Direct wind action combined with pH 3 acid mist resulted in the largest numbers of microscopic cuticular lesions, and the highest gc. By contrast, Direct wind action combined with pH 3 acid mist caused most visible damage to leaf tissue, but fewer microscopic lesions, and lower gc, than in plants treated with water mist. In severely-abraded leaves exposed to indirect wind action and low-pH acid rain, gc may be reduced by wound-isolation of blocks of non-functional leaf tissue.