Seasonal and diurnal patterns of monoterpene emissions from Pinus pinea (L.) under field conditions

Within the activity of the BEMA project (Biogenic Emission in the Mediterranean Area), the emission of volatile organic compounds from Pinus pinea L. was studied in a nature reservation close to Rome (Italy). Measurements were carried out during five campaigns from June 1993 to October 1994 using a dynamic branch enclosure technique. Investigations principally focused on studying diurnal and seasonal variability. P. pinea emitted mainly monoterpenes of which limonene, trans-β-ocimene, linalool, α-pinene, myrcene and 1,8-cineole were the most abundant. At a temperature of 30°C and PAR > 600 μmol photons m-2 s−1 the sum of emissions was about 2–3.5 μg g−1 leaf dry weight h−1 in spring and autumn, and about 7 to 15 μg g−1h−1 in summer. Absolute daytime emission rates were very high in summer (35 μg g−1 h−1 ) leading to a carbon loss of up to 8% of the 24 h photosynthetic carbon gain. α-pinene and limonene emissions were found in all campaigns and were emitted during day and night. Other compounds like trans-β-ocimene, linalool and 1,8-cineole occurred seasonally and were not or hardly emitted in the night. The lack of emissions during night point to a strong influence of light as confirmed by an artificial darkening experiment. Diurnal emissions of limonene and trans-β-ocimene were simulated by the monoterpene model. of Tingey et al. (1980, Plant Physiology 65, 797–801) and the isoprene model of Guenther et al. (1991, J. geophys. Res., 96, 10,799–10,808), using parameters suggested by Guenther et al. (1993, J. geophys. Res., 96 ,10,799–10,808) and parameters adjusted to data by best-fit regression analysis. Model predictions were fairly good with the adjusted parameters (R2 = 0.71 and 0.77, n = 139 and 72). Trans-β-ocimene data clearly fitted better with the isoprene model while Tingeyʹs monoterpene model was more appropriate for limonene data. The pronounced seasonality in amount and composition of the emissions demonstrate that the existing models describing the short-term response of emissions to temperature and light cannot always be used alone to estimate the annual monoterpene release from vegetation.