Instantaneous and historical temperature effects on a-pinene emissions in Pinus halepensis and Quercus ilex.

We compared the role of instantaneous temperature and temperature history in the determination of a-pinene emissions in Mediterranean conifer Pinus halepensis that stores monoterpenes in resin ducts, and in Mediterranean broad-leaved evergreen Quercus ilex that lacks such specialized storage structures. In both species, a-pinene emission rates (E) exhibited a significant exponential correlation with leaf temperature and the rates of photosynthetic electron transport (JCO 2+O 2) started to decrease after an optimum at approximately 35oC. However, there was a higher dependence of E on mean temperature of previous days than on mean temperature of current day for P. halepensis but not for Q. ilex. JCO 2+O 2 showed a maximum relationship to mean temperature of previous 3 and 5 days for P. halepensis and Q. ilex respectively. We conclude that although the best correlation of emission rates were found for instantaneous foliar temperatures, the effect of accumulated previous temperature conditions should also be considered in models of monoterpene emission, especially for terpene storing species.

Mass scans from a proton transfer mass spectrometry analysis of air over Mediterranean shrubland browsed by horses.

Plants usually emit large amount and varieties of volatiles after being damaged by herbivores. However, analytical methods for measuring herbivore-induced volatiles do not normally monitor the whole range of volatiles and the response to large herbivores such as large mammals is much less studied than the response to other herbivores such as insects. In this paper we present the results of using a highly sensitive proton transfer reaction-mass spectrometry (PTR-MS) technique that allows simultaneous monitoring of leaf volatiles in the pptv range. The resulting mass scans in air over Mediterranean shrubland browsed by horses show 70 to 100% higher concentrations of the masses corresponding to mass fragments 57, 43 and 41 (mostly hexenals, acetone and acetic acid) than scans over control non-browsed shrubland. These compounds are biogeochemically active and they are significant components of the volatile organic carbon found in the atmosphere. They influence the performance of living organisms and, the chemical and physical processes of Earth's atmosphere.