Isoprenoid emissions and physiological activities of Mediterranean macchia vegetation under field conditions

The emissions of volatile organic compounds, VOC, from plants have strong relevance for plant physiology, plant ecology and atmospheric chemistry. We report here the emission rates and the ecophysiological behaviour of the Mediterranean plant species Chamaerops humilis L., Pistacia lentiscus L. and Juniperus phoenicea L. Emission measurements made by means of a dynamic branch enclosure under field condition indicated that Chamaerops humilis is a strong emitter of isoprene at a diurnal rate of 41.4 ng m-2 s-1. Lower daily emission rates were measured for the monoterpene emitter shrubs P. lentiscus (13.9 ng m-2 s-1) and J. phoenicea (4.1 ng m-2 s-1) compared to C. humilis. A good correlation was found between isoprenoid emission rate and temperature. Monoterpene emission from the reservoir of Pistacia and Juniperus and isoprene released by Chamaerops leaves enhanced during periods of increasing irradiation and temperature in the middle of the day. The daily trends of photosynthesis showed higher values at morning and a greater CO2 assimilation in Pistacia lentiscus leaves compared to the other species. For leaf transpiration we observed a slight decrease in the afternoon in Chamaerops leaves and a fairly constant transpiration in the other two shrubs. Xylem water potential measurements indicated that all the species were not subjected to a severe drought stress.