Biogenic emission from the Mediterranean pseudosteppe ecosystem present in Castelporziano

Emission rates and fluxes of biogenic components emitted by a Mediterranean Pseudosteppe were measured in the BEMA test site of Castelporziano during the 1993 and 1994 field campaigns. Enclosure and micrometeorological techniques were used. Although the emission was comprised of isoprene, semi-volatile aldehydes, acetic acid and monoterpenes at trace levels, the most relevant compound in air was isoprene. Basal emission rates for isoprene (normalized at 30°C and 1000 μE PAR) as defined by Guenther et al. (1991, J. geophys. Res. 96, 10,799–10,808) were obtained for this ecosystem by combining experimental observations and predictions based on the Guenther algorithm. It is shown that the Mediterranean Pseudosteppe is a strong isoprene emitter with a basal emission rate of 0.45 μg m−2 s−1 during the flowering season. At the end of the maximum physiologically active season basal emission rate ranged only in 0.1–0.15 μg m−2 s−1. A close dependence from light and temperature for the isoprene emission is observed. The decline in emission rates seems to be associated with a reduction in photosynthetic activity linked to senescence of the vegetation present in this ecosystem. The results obtained indicate that the Mediterranean Pseudosteppe is an ecosystem characterized by a rapid and strong variability in isoprene emission. It represents a source of isoprene comparable to deciduous forest areas only during the flowering season (from the middle of March to the middle of May) whereas it becomes a minor source during the end of the maximum physiologically active season.