Field studies of isoprene emissions from vegetation in the Northwest Mediterranean region

During the Biogenic Emissions in the Mediterranean Area (BEMA) project field campaigns (1993 - 1997), 40 native Mediterranean plant species were screened for emissions of isoprene and monoterpenes using a branch enclosure sampling method with subsequent gas chromatographic-flame ionization detector (GC-FID) and GC-mass selective detector (MS) analysis. Thirteen species emitted more than 0.5 mu g (C) g(-1) dw h(-1) isoprene at 30 degrees C and 1000 mu mol m(-2) s(-1) photosynthetically active radiation (PAR), of which nine species emitted more than 20 mu g (C) g(-1) dw h(-1). Emissions of isoprene were strongly correlated with temperature and PAR, and were reasonably well predicted by existing algorithms. There was little intraspecies and day to day variation in base emission rates. In general, median base emission rates were higher in summer compared to autumn for most species. Significant difference in aggregated habitat base emission rates was found between dunes, garrigue, woodland, and riverside sample sites. Although considerable unexplained variability in base emission rates remains to be explored, first estimates of base emission rates for Mediterranean shrublands are presented here.