USE OF THE ISOPRENE ALGORITHM FOR PREDICTING THE MONOTERPENE EMISSIONFROM THE MEDITERRANEAN HOLM OAK QUERCUS-ILEX L - PERFORMANCE AND LIMITS OF THIS APPROACH

The algorithm developed by Guenther et al. [1991] to describe the orga nic emission of isoprene-emitting plants has been used for predicting monoterpene emission from Quercus ilex L., an evergreen oak typical of the Mediterranean basin. The dependence of monoterpene emission on ph otosynthetically active radiation and temperature has been verified th rough laboratory experiments carried out on single leaves as well as t hrough field measurements at branch level. While the algorithm describ es well monoterpene emission under stationary state conditions, it is less accurate when rapid fluctuations of light and temperature take pl ace. Because of this, the isoprene algorithm is capable of predicting the response of Quercus ilex L. with an accuracy better than +/-25% on ly in 65% of the environmental situations experienced by the plant. Fi eld and laboratory observations consistently indicate that temperature oscillations can be an important source for the discrepancies between predicted and observed values as they can generate bursts of emission with values twice as high as those predicted by the algorithm. Possib le causes generating these effects are analyzed and critically discuss ed. In spite of the observed limitations, the isoprene algorithm can s uccessfully describe the biogenic emission from Quercus ilex L., and i ts use is advantageous as it greatly simplifies regional and global em ission models, especially if the light dependence of monoterpene emiss ion is proven to be a widespread phenomenon.