STOMATAL CONDUCTANCE OF BIRCH LEAVES - PLENTY OF VARIATION IN THE VARIABLE WHICH DETERMINES THE OZONE DOSE

An observational study of the stomatal conductance of birch leaves was made. When three clones were compared, each clone showed its own char acteristic stomatal behaviour. Stomatal conductance also changes with age of the tree: leaves of young saplings have higher conductance than leaves of mature trees. Day-time stomatal conductance decreases stron gly towards the end of the growing season. Stomatal behaviour also cha nges in accordance with the environment, e.g. well watered experimenta l saplings can have high conductance as compared to saplings growing i n the soil. Differences between geographic (climatic) areas, habitats (mesic - xeric) and years (wet - dry) seem to be considerable and shou ld be studied further. On the basis of the large variation in stomatal conductance, it is hard to know how well one's experimental results c orrespond to the real field situations. (C) 1998 Elsevier Science Ltd.