Seasonal variation of monoterpene emission from Malus domestica and Prunus avium.

Emission rates of monoterpenes released by apple (Malus domestica Borkh) and cherry (Prunus avium L.) were estimated at different phenological stages. These measurements employed a dynamic flow-through Teflon chamber, sample collection onto cartridges filled with graphitized carbon and thermal desorption gas chromatography-mass spectrometry (GC-MS) for identification and quantification of the emitted volatiles. At full bloom the release of monoterpene hydrocarbons from cherry flowers was 1213 ng g(-1) dry weight (DW) h(-1), exceeding by approximately three-fold the emission rate of apple flowers (366 ng g(-1) DW h(-1)). Observed seasonal variations in biogenic volatile organic compound (VOC) emissions ranged over several order of magnitudes. At fruit-set and ripening stages, in fact, the hydrocarbon emission dramatically decreased reaching the lowest values at harvest time when leaves were fully mature (3-9 ng g(-1) DW h(-1)). Wide diversity in the composition of compounds from the species studied was also recorded. At blooming, linalool contributed significantly to the monoterpene emission from apple (94% of the emitted carbon) while alpha-pinene and camphene represented on average more than 60% of the total emitted volatiles from cherry flowers. Among the monoterpenes identified in flowers, alpha-pinene, camphene and limonene were also found in the foliage emission of both species. Fruit trees are relevant monoterpene emitters only at blooming and thus for a short period of the vegetative cycle. When leaves are fully developed, the carbon loss due to monoterpene emissions related to the photosynthetically carbon gain is negligible.