Effects of elevated [CO2] and O-3 on stomatal and surface wax characteristics in leaves of pubescent birch grown under field conditions

The responses of pubescent birch (Betula pubescens Ehrh.) leaves to elevate d levels of carbon dioxide and ozone were investigated. The micropropagated birch clones used in this research were divided into coastal (Kempele 64 d egreesN degrees 25E) and inland (Ylikiiminki 65 degrees N 26 degreesE) clon es according to the provenance of the parent tree. The seedlings were expos ed to elevated levels of CO2 and CO2+O-3 in open-top chambers over four gro wing seasons (1993-1996). The leaves used in this investigation were gather ed in 1995 and 1996. Leaf characteristics seemed to be dependent on leaf ag e and weather conditions. Stomatal density was greater in plants grown in o pen-top chambers relative to unchambered controls. The CO2 and CO2+O-3 trea tments did not affect the stomatal density of the birches. However, the mea n stomatal size of the coastal clone increased significantly (13%) in the C O2 treatment compared with the filtered and ambient controls in 1995. In 19 96, the mean stomatal sizes of the Inland clones were also significantly hi gher in the CO2 (10%), CO2+O-3 (11%) and non-filtered (12%) treatments comp ared with the filtered control. The distribution of wax deposits on the aba xial leaf surface increased in the inland clone under elevated levels of CO 2. The growth environment affected the development of the epicuticular waxe s: non-filtered air, CO, and CO2+O-3 treatments seemed to stimulate the for mation of wax deposits compared with the charcoal filtered control in which wax formation was the weakest. The combined effects of elevated CO2 and O- 3 levels on the stomatal size and epicuticular wax deposits were similar in comparison to the effects of elevated CO2 levels atone.