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 characteristic 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 strongly towards the end of the growing season. Stomatal behaviour also changes in accordance with the environment, e.g. well watered experimental saplings can have high conductance as compared to saplings growing in the soil. Differences between geographic (climatic) areas, habitats (mesic - xeric) and years (wet - dry) seem to be considerable and should be studied further. On the basis of the large variation in stomatal conductance, it is hard to know how well oneʹs experimental results correspond to the real field situations.