Effects of elevated CO2 and temperature on monoterpene emission of Scots pine (Pinus sylvestris L.)

The aim of this study was to evaluate the long-term (5 years) effects of elevated CO2 concentration (doubling of ambient CO2 concentration) and temperature (2–6 °C elevation) on the monoterpene emission of Scots pine (Pinus sylvestris L.) saplings (ca. 20 years old) grown in closed-top environmental chambers. The chamber treatments included: (1) ambient temperature and CO2, (2) ambient temperature and elevated CO2, (3) elevated temperature and ambient CO2, and (4) elevated temperature and elevated CO2. The variability of emissions during and after tree shoot growth was studied, and additionally the total cumulative emission of monoterpenes through a growing period (May–September) was estimated. When compared to the controls, the combination of elevated CO2 and temperature significantly increased normalized monoterpene emission rate for the whole growing period (+23%), whereas elevated CO2 had no significant effect (−4%), and elevated temperature even decreased (−41%) the emission rate. The increasing effect of the combination of elevated CO2 and temperature was strongest during shoot growth (+54%). After shoot growth, no significant differences in emission rate were found among the treatments. Emission modeling showed that the total amount of monoterpenes emitted from May to September was 2.38 mg gdw−1 in ambient conditions. The total emission in elevated CO2 was 5% greater and in elevated temperature 9% lesser than in ambient conditions. The combination of elevated CO2 and temperature increased the amount of emitted monoterpenes over the growing period by 126% compared to the total emission in ambient conditions.