EMISSION OF SHORT CHAINED ORGANIC-ACIDS, ALDEHYDES AND MONOTERPENES FROM QUERCUS-ILEX L. AND PINUS PINEA L. IN RELATION TO PHYSIOLOGICAL ACTIVITIES, CARBON BUDGET AND EMISSION ALGORITHMS

We report on the emission of monoterpenes, short-chained organic acids and aldehydes from Mediterranean oak (Quercus ilex L.) and pine (Pinu s pinea L.). All studies were done with dynamic cuvettes enclosing int act branches at the top of the canopy flushed with ambient air. Daily trends are compared with the photosynthetic active radiation (PAR), le af temperature and the physiological activities of the enclosed branch es, i.e. assimilation and transpiration, with special attention on the carbon budget. Oak emits monoterpenes in high amounts, up to 2% of th e assimilated carbon. As compared with monoterpenes, short-chained org anic acids and aldehydes are of minor importance for oak. However, on a leaf dry-weight basis equal amounts of acids and aldehydes are relea sed from oak and pine. As pine emitted only low amounts of terpenes (b elow 0.2% of the assimilated carbon) the release of terpenes and oxyge nated compounds is of equal importance for this species. A comparison of a modelled light and temperature driven emission with the observed volatile organic compounds (VOC) emissions showed good agreement for m onoterpenes as well as for organic acids emitted in the case of oak. F or pine only the release of acids showed an adequate relation to the a lgorithm data, whereas the terpene emissions seemed to be dominated by temperature effects. (C) 1997 Elsevier Science Ltd.