Abstract
Abstract. Plants emit significant amounts of monoterpenes into the earth's atmosphere, where they react rapidly to form a multitude of gas phase species and particles. Many monoterpenes exist in mirror-image forms or enantiomers. In this study the enantiomeric monoterpene profile for several representative plants (Quercus ilex L., Rosmarinus officinalis L., and Pinus halepensis Mill.) was investigated as a function of chemotype, light and temperature both in the laboratory and in the field. Analysis of enantiomeric monoterpenes from 19 Quercus ilex individuals from Southern France and Spain revealed four regiospecific chemotypes (genetically fixed emission patterns). In agreement with previous work, only Quercus ilex emissions increased strongly with light. However, for all three plant species no consistent enantiomeric variation was observed as a function of light, and the enantiomeric ratio of α-pinene was found to vary by less than 20% from 100 and 1000 μmol m−2 s−1 PAR (photosynthetically active radiation). The rate of monoterpene emission increased with temperature from all three plant species, but little variation in the enantiomeric distribution of α-pinene was observed with temperature. There was more enantiomeric variability between individuals of the same species than could be induced by either light or temperature. Field measurements of α-pinene enantiomer mixing ratios in the air, taken at a Quercus ilex forest in Southern France, and several other previously reported field enantiomeric ratio diel cycle profiles are compared. All show smoothly varying diel cycles (some positive and some negative) even over changing wind directions. This is surprising in comparison with variations of enantiomeric emission patterns shown by individuals of the same species.
Highlights
Terrestrial vegetation is an important global source of reactive volatile organic compounds (VOCs) contributing circa 1 Pg (1 × 1015 g) of carbon annually (Guenther, 2002), approximately ten times more than the estimated sum of anthropogenic VOC emissions, including fossil fuel and biomass burning (Piccot et al, 1992)
We examined enantiomeric monoterpene emissions as a function of temperature and light under controlled laboratory conditions using three plant species that represent different types of monoterpene producers: Quercus ilex, an evergreen sclerophyllous oak, which is one of the most widespread tree species in the Mediterranean Basin and emits large amount of monoterpenes, was chosen as a representative emitter of non-stored monoterpenes whose emission is essentially controlled by the rate of biosynthesis
BVOC emissions are strongly modulated by the biotic and abiotic environment, their compositional fingerprints have been used as chemotaxonomic markers in order to better understand the geographical distribution of certain species www.biogeosciences.net/11/1435/2014/
Summary
Terrestrial vegetation is an important global source of reactive volatile organic compounds (VOCs) contributing circa 1 Pg (1 × 1015 g) of carbon annually (Guenther, 2002), approximately ten times more than the estimated sum of anthropogenic VOC emissions, including fossil fuel and biomass burning (Piccot et al, 1992). In this case the emission rate of the monoterpene to the atmosphere is observed to increase exponentially with increasing leaf temperature In other species such as the Mediterranean oak (Quercus ilex), no significant storage pool exists and the monoterpene emission occurs (in similar fashion to isoprene) when light is present (Guenther et al, 1993; Loreto et al, 1996a; Staudt and Seufert, 1995). It is possible that in Pinus halepensis and Rosmarinus officinalis two pools exist, as has been demonstrated for Norway spruce and Scots pine (Ghirardo et al, 2010) If both de novo and storage emission types exist that produce exactly the same enantiomers, emissions should show no light dependence in enantiomeric ratio (i.e. there are emissions in the dark that increase with light but with the same enantiomeric pattern). For more accurate ecosystem response modelling, especially with regard to future climate changes, it will be necessary to link atmospheric chemistry models to ecological models including biological, mechanical and environmental stresses
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