Emission of volatile organic compounds from two silver birch (Betula pendula Roth) clones grown under ambient and elevated CO2 and different O3 concentrations

We analysed the emission of volatile organic compounds (VOCs) from two clones (4 and 80) of silver birch (Betula pendula Roth) trees exposed to doubled ambient CO2 and O-3 singly and in combination, in open-top chambers. VOCs were collected in July and in August from detached twigs. The effect of twig detachment as such on emissions was separately studied, and it increased the emissions of green leaf volatiles. The emission in July from both clones was dominated by sesquiterpenes (SQTs) germacrene D, (E,E)-alpha-farnesene, alpha-copaene and beta-bourbonene, while in August, the emission was dominated by monoterpenes (MTs) (E)-beta-ocimene and (Z)-ocimene. Elevated CO2 concentration marginally decreased total NIT emission in July, while in August the total NIT emission was enhanced by elevated CO2. O-3 or CO2 + O-3-exposure did not have any effect on total NIT or total SQT emissions. In general clones 4 and 80 emitted total quantified VOCs (19 compounds) 12520 and 8590 ng g(-1) fw h(-1) in July, and 4640 and 4990 ng g(-1) fw h(-1) in August, respectively. Clone 4 emitted more beta-pinene + myrcene, (Z)-ocimene and (E)-beta-ocimene in July than clone 80, which emitted more linalool in July, and hexanal in August than clone 4. Elevated CO2 tended to decrease the emissions of nonanal and (E)-beta-ocimene in July, while O-3 and CO2+O-3 had no effects on emissions. Our results indicate that elevated CO2 and O-3 concentrations do not have considerable effect on silver birch emissions by increasing the carbon allocation to VOCs or by inducing the emission of novel compounds. Other factors, such as temperature, light and herbivores might conceal the effects of these atmospheric gases. High SQT proportion in emission profile suggests that B. pendula may have substantial role in biogenic aerosol formation in boreal forests. (C) 2004 Elsevier Ltd. All rights reserved.