DIURNAL AND SEASONAL COURSE OF MONOTERPENE EMISSIONS FROM QUERCUS-ILEX (L.) UNDER NATURAL CONDITIONS - APPLICATIONS OF LIGHT AND TEMPERATURE ALGORITHMS

Quercus ilex is a common oak species in the Mediterranean vegetation a nd a strong emitter of monoterpenes. Since the short-term control of m onoterpene emissions from this species involved both temperature and l ight, the usual exponential function of temperature may not be suffici ent to model the diurnal and seasonal emission course. In the frame of the BEMA-project (Biogenic Emissions In the Mediterranean Area), we i nvestigated the tree-to-tree, branch-to-branch, diurnal, and seasonal variability of monoterpene emissions from Q. ilex over one and a half years at Castelporziano (Rome, Italy). In addition, we checked the sui tability of the model developed for isoprene by Guenther et al. (1991, 1993) to simulate the short-and long-term variations of monoterpene e missions from this particular species. We found that the tree-to-tree variability was rather small compared to the experimental error during air sampling and analysis by diverse laboratories. The branch-to-bran ch variability was noticeable between sun-and shade-adapted branches o nly. 80% of total emissions were represented by alpha-pinene, beta-pin ene and sabinene, whose proportions were stable over the year and inde pendent of light exposure. The emission factor (emission rate at 30 de grees C and 1000 mu mol photon m(-2) s(-1)) estimated by the isoprene model or extrapolated from measurements was similar: it was about 22 m u g g dw(-1) h(-1) for sun-exposed branches and 2.3 mu g g dw(-1) h(-1 ) for shade-adapted branches. It was rather stable over the seasons ex cept during leaf development. The diurnal and seasonal emission patter ns From Q. ilex were simulated in a satisfying way by Guenther's algor ithms especially if we excluded the laboratory variability. For shade- adapted branches, an emission factor 17 times lower had to be applied, but temperature and light responses were unchanged. (C) 1997 Elsevier Science Ltd.