CUTICULAR AND STOMATAL ANTECHAMBER CONDUCTANCE TO WATER VAPOUR DIFFUSION IN PICEA ABIES (L.) KARST.

This thesis presents a detailed analysis of two components of water vapour diffusion from the needles from Picea abies (L.) Karst. — water loss through the stomatal antechambers and minimum water loss through the cuticle. The dimensions of stomatal antechambers and the number of the stomata per unit leaf area were determined in light and shade needles of 9... 100-year-old spruce trees. The results showed that despite the pronounced differences in antechamber dimensions in sun and shade needles, the calculated resistance of a single stomatal antechamber to water vapour diffusion was similar. Ante­ chamber resistance per unit of leaf area depends on stomata density. In the case of fully opened stomata, the proportion of antechamber resistance exceeded a third of the total resistance to water vapour diffusion. The variability of minimum epidermal water losses has been studied by direct measuring of water loss from the desiccating needles and by two indirect methods which were used to evaluate the changes of the epicuticular wax layer. The indirect methods were the droplet contact angle method showing the wet­ tability of the needle surface and the SEM studies showing the structure of epicuticular wax. In all these cases variability between different needle ageclasses and positions in the tree crown were studied. Attention was also paid to the influence of several air pollution situations occurring at various sites of Estonia. Needle wettability increased in the course of needle ageing. In the lower part of the tree crown the increase of minimum epidermal conductance during needle ageing was faster than in the upper crown. However, the needles from two neighbouring trees showed larger differences in wettability than the trees growing at sites with different air pollution load. Removal of wax decreased wettability. Therefore I conclude that droplet contact angle method is not suitable for monitoring air pollution in Estonia. Epicuticular wax on current year shade needles was more degraded than in sun needles. In half-year-old needles from adult spruces at 12 sites of Estonia no crystalloid wax was found. Despite the different exposure of the study sites to air pollution, the wax degradation from tubular into flattened structures at the sites was similar. The observations of epicuticular wax structures of young monoclonal spruces five years later showed slower degradation speed. How­ ever, great variability in wax structure within a sample and even within the same needle was found. There was no correlation between wax degradation and the overall air pollution level. In the cause of needle ageing their minimum epidermal conductance in­ creased. The conductance of sun and shade needles of a forest tree was differ­ ent. At open sites there were no universal trends in correlation of minimum