Emissions from vegetation provide a major source of reactive volatile organic compunds relevant fro the production of ozone and photochemical oxidants in the troposphere. Orchards cover large extensions of European territory. In these regions the production of peach, apple, pear, grapes and other fruits is economically important because of both the internal request and the export to North- and extra-European countries. The emission from fruit trees may become relevant in correspondence of short-term events, such as flowering or pest attacks, or during long-term growth processes. For instance, there is evidence that many volatile organic substances are produced and emitted from the beginning of the ovary growth to fruit ripening. Agricultural practices, while regulating the relationships between sink and sources, can also influence the VOC emission either directly (fruit reduction) or indirectly (emission from wounded tissues). Orchard architecture, namely arrangement of trees in rows, regulation of biomass, growth, and branching patterns as well as differences in leaf orientation during vegetative and productive season, strongly influence the light and temperature regimes of the canopy, and, in turn, may modify the emission pattern.
The task of this paper is to quantify the VOC emission from orchards as related to physiology, architectural features, and phenological phases. VOC emission by the most important fruit species has been measured in different phenological and growth stages in laboratory-based experiments in which leaves, flowers, and fruits have been maintained under conditions which are favourable to VOC emissions and the volatile compounds have been identified and quantified by gas chromatography-mass spectrometry (GC-MS). The emission from two-year-old potted plants of emitting species maintained in a growth-chamber have been monitored in order to test the whole canopy contribution to the emission rate in different phenological and growth stages. These experiments are preliminary to open field measurements utilising the branch enclosure technique on leafy shoots and on shoots bearing fruits of trees at different growth stages on trees in which the main parameters driving VOC emission (light and temperature) will be measured in order to describe the hourly, daily and seasonal evolution of canopy light transmittance and the biomass thermal regime. Since the phytometric indexes are the main modulators of tree light interception and atmospheric coupling, different orchard organizational systems will characterized in their sourse/sink distribution and physiology.