ISOPRENOID EMISSION OF OAK SPECIES TYPICAL FOR THE MEDITERRANEAN AREA- SOURCE STRENGTH AND CONTROLLING VARIABLES

Measurements of isoprenoid emission on five Mediterranean Oak species in the field revealed that Quercus frainetto, Quercus petraea and Quer cus pubescens are strong emitters of isoprene. In contrast Quercus cer ris and Quercus suber emitted no significant amounts of isoprene and m onoterpenes. For Q. pubenscens and Q. frainetto median emission factor s of 16.68 nmol m(-2) s(-1) (86.06 mu g g(-1) dw h(-1)) and 30.72 nmol m(-2) s(-1) (133.95 mu g g(-1) dw h(-1)) were calculated, respectivel y. The 25 to 75 percentiles span of the emission factor data sets rang ed from -53% to +56% of the median values. Light and temperature are t he main controlling factors for isoprene emission. The influence of ot her environmental and plant physiological parameters on the isoprene e mission is discussed. The ''Guenther'' emission algorithm is able to p redict the daily maximum of the isoprene emission within the plant spe cific uncertainty range. However, the morning increase and the afterno on drop in the isoprene emission is not well parameterized. On the bas is of process oriented models for the synthesis of isoprene in plants, a further reduction in the uncertainty may be achieved resulting in a more reliable prediction of short-time variation in isoprene emission . (C) 1997 Elsevier Science Ltd.